REFURBISHMENT OF CONCRETE BUILDINGS:

Transcription

1 Guidance Note GN 8/99 REFURBISHMENT OF CONCRETE BUILDINGS: Structural & services options C A Gold, BCA A J Martin, BSRIA

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3 Guidance Note GN 8/99 REFURBISHMENT OF CONCRETE BUILDINGS: Structural & services options C A Gold, BCA A J Martin, BSRIA The Building Services Research and Information Association Old Bracknell Lane West, Bracknell, Berkshire RG12 7AH Tel: + 44 (0) Fax: + 44 (0) [email protected]

4 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means electronic, mechanical, photocopying, recording or otherwise without prior written permission of the publishers. ISBN Printed by Oakdale Printing Co. BSRIA October 1999

5 SUMMARY SUMMARY It is estimated that there is currently 8 million m 2 of redundant office space in the UK, much of which was constructed in the 1960s and 1970s in reinforced concrete. These buildings, and others from the 1980s, 1990s and pre-and post-world War II, have the potential to provide the standards of accommodation required in the 21st century, with increased energy efficiency, if refurbished in the correct manner. This publication provides guidance for structural and building services engineers on building refurbishment options. The emphasis is on office buildings, but much of the information is applicable to other building types. There is also growing interest in change of use for redundant office buildings, such as converting them into student accommodation, flats or hotels. This document is the second of three publications concerned with refurbishment of concrete buildings. The first publication is intended for the owners of buildings and their advisers and covers the factors influencing the decision to refurbish in general terms. The third publication details approaches that should be considered in the design of new buildings so that they will be more adaptable to future changes in requirements. Chapter 1 of this publication provides an introduction to the refurbishment of buildings, including the need to refurbish and viability of refurbishment. The main reasons for refurbishing a building are: to improve the building aesthetics to increase net lettable floor area changes in regulations changes of use need to upgrade services. The levels of refurbishment are: minor/cosmetic intermediate structure or services major complete. Chapter 2 describes the characteristics of old office buildings. Pre- World War II and 1950s and 1960s buildings generally have narrow floor plates and services are routed around the perimeter. The older buildings have high ceilings but those dating from the 1950s/60s have low floor to ceiling heights. Buildings completed in the 1970s have larger floor to ceiling heights and are deep plan. Many concrete buildings constructed in the 1960s and 1970s are made of precast concrete. BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options

6 SUMMARY Chapter 3 considers the condition surveys that need to be carried out prior to refurbishment to assess the condition of the existing building services and the structural integrity of the building shell. Chapter 4 considers the interaction between structural and services work and the issues affecting services selection. The effect of the structural elements used in the building construction and the restrictions on horizontal and vertical routing of services are discussed. Chapter 5 describes building services refurbishment options, ranging from issues concerning the facade to ventilation, heating, cooling, air conditioning, lighting and electrical installations. Chapter 6 details structural modification options. Concrete repairs are described together with methods to accommodate increased loadings. Solutions suitable for capacity enhancement of various elements are summarised and these are illustrated with short case studies. Methods of accommodating geometry changes are also detailed, ranging from removal of suspended ceilings where storey heights are limited, to the creation of openings in slabs, beams and walls. Methods for increasing floor area are described including relocation of services, construction of additional floor plates and construction of additional storeys. Chapter 7 describes case studies to illustrate the feasibility of refurbishment options. The case studies include: office building services refurbishment - Howard House, Bristol where the life of the services had expired conversion of factory areas to office accommodation - Boots D10 Building, Nottingham building services refurbishment to improve the internal environment and increase net floor area at the DTI, London addition of escalators and stairs - Allders Department Stores, Croydon and Portsmouth complete office building refurbishment - No. 1 Neathouse Place, London office to hotel refurbishment. Appendix A details legislation affecting building refurbishment. Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

7 ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS This work was carried out under the Department of the Environment, Transport and the Regions Partners in Technology programme DETR Ref 38/13/22 (cc. 1399). The project was managed by FBE Management Ltd. Department of the Environment, Transport and the Regions. The project was undertaken by the British Cement Association (BCA) and the Building Services Research and Information Association (BSRIA) with additional contributions from the Reinforced Concrete Council (RCC) and John Clarke, an independent consultant now with the Concrete Society. Thanks are also due to Dr A Jones, formerly with BCA, who was involved in formalising the project in its early stages. BCA and BSRIA would like to thank the following steering group members for their contribution to the project: Mike Cooke, Buro Happold Terry Payne, Monodraught Ltd Nick McMahon, Nick McMahon Ltd Martin Southcott, Reinforced Concrete Council Graham Charlesworth, Ridd Wood Partnership Brian Lacey, Sure Foundation Building Services Ltd. Whilst every opportunity has been taken to incorporate the views of the steering group, final editorial control of this document rests with BSRIA. DISCLAIMER All advice or information from the Building Services Research and Information Association and the British Cement Association is intended for those who will evaluate the significance of its contents and take responsibility for its use and application. No liability (including that for negligence) for any loss resulting from such advice or information is accepted. Cover photo courtesy of Martine Hamilton Knight BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options

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9 CONTENTS CONTENTS 1 INTRODUCTION Concrete buildings - a valuable asset Reasons for refurbishment Aesthetics Requirement to increase net lettable floor area Change in Regulations Change of use Need to upgrade services Levels of refurbishment Refurbishment costs CHARACTERISTICS OF BUILDINGS OF DIFFERENT AGES AND THEIR IMPLICATIONS FOR REFURBISHMENT Office buildings Pre-World War II offices Late 1950s/1960s offices s offices s offices s offices Future offices Other buildings Housing/hotels Serviced office space Methods of construction In situ construction Precast construction CONDITION SURVEYS PRIOR TO REFURBISHMENT Assessing the condition of existing building services Automatic control systems Fire alarm systems Electrical installation Lighting installation Boiler system/domestic hot water systems Ventilation systems Cooling systems Lifts and escalators Pipework Ductwork Facade (windows, air tightness, insulation) Assessing the condition of the existing structure Subsoil and foundation conditions Reinforcement corrosion Concrete condition Structural problems Structural capacity Structural stability Load tests BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options

10 CONTENTS 4 INTERACTION BETWEEN STRUCTURAL AND SERVICES WORK Loadings Geometry of the structure Selection of services Routing of services General Vertical distribution Horizontal distribution Distribution solutions Fixings from floor slabs BUILDING SERVICES REFURBISHMENT OPTIONS Overview Facade General requirements Insulation requirements and methods of provision Windows Air infiltration through the facade - air leakage testing Shading systems - internal, external, mid-pane, solar control glass Daylighting Ceilings and floors Ventilation and air-conditioning General refurbishment ventilation strategy Natural ventilation strategy Mixed mode systems Mechanical ventilation and air conditioning Centralised systems Localised systems Heating and hot water Electrical services Lighting installation Electrical installation SOLUTIONS TO STRUCTURAL PROBLEMS/OBSTACLES Concrete repair Non-structural concrete repairs Structural concrete repairs Coatings/barrier systems Repairs to fire damaged concrete Increased loadings General Increasing the capacity of floors and beams Increasing the shear capacity of beams at supports Increasing the punching shear capacity around columns Increasing the load capacity of columns Increasing the moment capacity at supports Increasing the lateral stability Increasing the load capacity of the foundations Summary of methods for increasing load capacity Spatial changes Limited storey height Removal of a column Creating openings in slabs Creating openings in beams and walls Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

11 CONTENTS Demolition of prestressed elements Creating an atrium by partial demolition Increasing the floor area Adding an additional floor Visual appearance Basements Cladding CASE STUDIES Introduction Building services Structural REFERENCES APPENDICES APPENDIX A BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options

12 CONTENTS FIGURES Figure 1 Part load efficiencies of boilers [33] Figure 2 One main riser through the building [65] Figure 3 Distributed risers [65] Figure 4 Services fed from a central corridor Figure 5 External distribution of ducts [65] Figure 6 Possible fixings to soffits in voided construction Figure 7 Possible fixings to soffits of exposed ribs Figure 8 Types of air conditioning system [59] Figure 9 Chilled ceiling panel Figure 10 Tendon cutting sequence Figure 11 City Point stripped back to the frame Figure 12 View of stripped-out floor Figure 13 Building stripped back to concrete frame Figure 14 New glazing TABLES Table 1 Levels of refurbishment... 5 Table 2 RC frame and member types Table 3 Life factors for M&E plant and systems [21] Table 4 Checklist of building services issues Table 5 Historic RC design codes [51, 52, 53] Table 6 Historic codes for design loads Table 7 Foundation load reduction factors Table 8 Allowable modifications to structural elements Table 9 Attributes of air conditioning systems for refurbishment (adapted from Good Practice Guide 71) [59] Table 10 Standard U-values [32] Table 11 Benefits/disadvantages of natural ventilation Table 12 Potential benefits/disadvantages of centralised systems Table 13 Benefits/disadvantages of localised systems Table 14 Relative air conditioning capital and running costs (1993) (based on gross floor area) [59] Table 15 Structural strengthening options Table 16 The Efficiency Requirements Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

13 INTRODUCTION SECTION 1 1 INTRODUCTION 1.1 CONCRETE BUILDINGS - A VALUABLE ASSET It is estimated that currently 8 million m 2 of UK office space requires refurbishment, much of which was constructed in reinforced concrete. These buildings have the potential to provide the standards of accommodation required in the 21st century if refurbished in the correct manner. There are many factors influencing the refurbishment of concrete buildings and this Guide presents refurbishment options for structural and building services engineers. Concrete buildings dating from the 1960s and 1970s and earlier offer several benefits compared with their more recently constructed counterparts. These benefits are: the buildings are often in a favourable location refurbishment is quicker and generally cheaper than demolition and reconstruction the buildings are higher and have a larger footprint and more car parking than would be allowed under current planning regulations narrower floor plates and natural ventilation often found in these buildings meet expectations for buildings where windows can be opened. Occupants are more tolerant of poorer internal environments if they have greater control over the environment in their space air conditioning can be added where required there is a shortage of large buildings and this may add value to the refurbishment. The refurbishment market is almost as large as the new build market with 48% of building work being repair and maintenance [1]. This is predicted to grow faster than new work and eventually overtake it. Approximately 10% of office space is refurbished in some form every year [2]. Possession of refurbished concrete buildings has been proven to be viable economic stock. If a building is part of a portfolio it may be possible to remove it from the rental market for, say eighteen months, refurbish it and then return it to the market with the increased rental income repaying the investment. There is much less prejudice against concrete buildings than there used to be. Whilst problems with concrete buildings can exist, (see Section 3.2) the problems are known and can generally be overcome. There are many examples of successfully refurbished concrete buildings, as illustrated in the case studies at the end of this Guide. Improvements that have been carried out to concrete buildings include: reduction in floor loadings by removing floor screed extension of floor plates, perhaps adding 20% to net lettable area addition of lift shafts, risers, and escalators upgrading ventilation and air conditioning systems addition of solar shading addition of floors or extension to building. BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 1

14 SECTION 1 INTRODUCTION This publication, the second in a series of three, deals with the technical details of the replacement or refurbishment of building services and the structural modifications that are commonly encountered during the refurbishment of concrete buildings. The management and procurement issues associated with building refurbishments are covered in CIRIA Report 33 [3] and are not repeated here. The reasons for refurbishment from a client's viewpoint are set out in the first publication in this series [4]. These are also described briefly in the following section. 1.2 REASONS FOR REFURBISHMENT In a recent survey on behalf of The Royal Institution of Chartered Surveyors (RICS) [2] availability of car parking, flexibility of floor plates for fit-out, the indoor working environment and proximity to transport links were cited as the top four criteria affecting tenants' choice of office properties. When selecting office space, businesses require flexible space that can respond to organisational changes and business developments. The growing importance of the need to optimise use of business space and the environmental conditions within it is demonstrated by the growth of facilities management as a profession. Many occupied buildings do not meet all the ideal criteria noted above. Whilst some elements are not changeable, such as location, other aspects can be readily upgraded to improve working and organisational conditions as well as to maximise asset/rental income value. However, not all refurbishment work will be financially viable and every case requires individual assessment. Nonetheless, it is increasingly found that refurbishment provides more than adequate returns on investment. The alternative to refurbishment of an existing building is to demolish it and build a brand new one. This, however, is costly in monetary and sustainability terms (through the greater use of raw materials), as well as in terms of programme, as planning permission will have to be sought, particularly if a change of use is involved. The lettable area for the replacement is likely to be much less than the original building, making refurbishment a more attractive option. A further benefit is that it may be possible to phase the refurbishment so that part of the building remains occupied, thus generating income. It should also be remembered that refurbishment is significantly less time-consuming than demolition and rebuilding, perhaps taking two thirds of the time. When the cost of finance and the loss of rental income are taken into account this represents a significant sum. The principal reasons for refurbishment are given in the following sections Aesthetics The appearance of a building is particularly important. A poor exterior or interior appearance will influence market perception of the building and will deter many companies from taking a tenancy. Refurbishment of parts of the building such as the facades, entrance or other public areas, will overcome this. Credibility can be given to a building by giving it a better appearance and even linking it with a big name architect. 2 Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

15 INTRODUCTION SECTION 1 However, aesthetic upgrading could impose greater loads on a structure. For example, replacement of existing cladding with something heavier, eg louvred windows, would require that these loads can be adequately transferred to elements capable of sustaining them and that the building foundations can accommodate these loads Requirement to increase net lettable floor area One way of greatly enhancing the value of a building is to be able to collect more rent from it. This can be achieved by increasing the net lettable floor area and is discussed in Section Change in Regulations There are many national Regulations, British Standards and local Acts, as well as property developers' expectations that have to be taken into account during building refurbishment. From the structural point of view, there may be a requirement for increased design floor loading greater than the minimum specified in design codes. Also, recommended design floor loads and recommended wind loads (BS 6399 [5] ) have changed over time. Reinforced concrete design codes have changed constantly over time. Changes to the Building Regulations have increased fire resistance periods and altered requirements for access and facilities for disabled people. Servicesrelated Regulations include those imposed by the Workplace (Health, Safety and Welfare) Regulations, 1992 [6], which applied retrospectively to all buildings from 1996 and required, for example, lighting, heating and ventilation to meet minimum standards. The regulations that influence refurbishment are discussed in Appendix A. There may be future changes in Regulations and in local or national policies, such as the move towards integrated transport and to restrict the use of private cars in towns, which would reduce the need for car parking and hence make space available for conversion to other use. Current Government moves to restrict out-of-town development and regenerate inner cities are encouraging the conversion of offices to residential and other uses Change of use Many refurbishments are brought about by changes in organisational requirements. Space needs are constantly changing as whole companies, departments, and teams of workers expand and contract. This leads to internal moves taking place, at which point the decision is made to refurbish while the space is clear. Other changes of use relate to conversion of parts of a building to other uses, such as storage areas to office space, or offices to dining areas. However, where higher average occupancy of a building is brought about by changed working patterns, there may be a requirement for increased facilities such as toilets as well as a need to install additional staircases, lifts and escalators. These will require major structural alterations, as discussed in Section 6. BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 3

16 SECTION 1 INTRODUCTION At a social level, developing technology and changes in working patterns are predicted to affect the use of buildings, particularly office space. Growth in the use of office automation and information technology has led to increased working from home or elsewhere and the export of repetitive, simple operations to developing countries. Consequently, office environments are changing. This is considered in more depth in the third publication Refurbishment of concrete buildings: Designing now for future re-use [7]. There is also a growing interest in overall changes of use, for example, changing redundant offices into residential flats or student accommodation. This has been brought about by over-supply of office space during the early 1990s leading to many buildings being unlettable. These buildings can often meet market need for residential, hotel or leisure buildings, the increased rental income or asset value paying for the conversion. This has been aided by regeneration of urban areas making previously undesirable areas attractive. However, overall changes of use are geography-dependent. For instance, in London there is currently much need for office-to-office and office-to- hotel refurbishments, while in Bristol there is more need for office-to-student accommodation refurbishments Need to upgrade services One of the primary reasons for refurbishment from a services perspective will be the need to upgrade or replace existing plant because of a poor working environment caused by ineffective air conditioning, heating or ventilation. This is considered in more detail in Section 5. In some cases there will be reduced cooling requirements in some areas of the building (eg less heat from more efficient modern electronic equipment). In other cases there may be an increased cooling requirement, for example due to hot desking leading to a higher average occupancy of the building. Refurbishment of services will provide the opportunity for a more energy efficient building with consequent cost savings, an area in which future legislation may have a significant impact. Other reasons for building services refurbishment relate to the upgrading of electrical services and office communications to meet changing business needs and the upgrading of other systems such as fire/security and building management to provide greater functionality. 1.3 LEVELS OF REFURBISHMENT The extent of building refurbishment will vary for each job and it is not possible to give definitive levels. There will, for example, be situations where a major refurbishment is carried out on one part of the building, such as the entrance hall, but only a minor refurbishment elsewhere. However, refurbishment can be broadly classified as shown in Table 1. The typical cost and time to recoup the investment based on the increased rent obtainable for different refurbishment levels is based on previous surveys [2,8] and consideration of cost breakdowns given in journal articles on refurbishment. 4 Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

17 INTRODUCTION SECTION 1 Table 1 Levels of refurbishment Type Cost /m 2 Approximate time to carry out (months) Minor/ cosmetic Approximate payback period (years) Description This will involve redecorating, improving signage and lighting, replacing floor coverings, exterior painting and repair, minor changes to the fittings. Typically takes place at 5-year intervals. Services Complete replacement of heating, ventilation and air-conditioning plant. Associated pipework, ducting, terminal units, controls and insulation may be replaced or upgraded as necessary. Typically takes place at 25 year intervals (control systems more frequently). Structural Addition of new lift shaft, escalators or riser, necessitating structural alterations. Major This will involve major changes to the services and the interior fittings but without any significant structural alterations. May include addition of raised floor, improvements to core areas and entrance halls, new lighting, internal shading. Typically takes place at 25 year intervals and in conjunction with a lease renewal. Complete This will involve significant structural alterations, such as the extension of the floors or partial demolition to create an atrium or stripping of the building back to the concrete frame. New cladding may be fitted together with the installation of new services and full fitting out. Timing of a complete refurbishment is variable but likely to take place in conjunction with a lease renewal. New Build Construction of a new building, excluding demolition of an existing building and loss of rent Refurbishment costs Refurbishment projects tend to involve more uncertainty and risk than new-build projects. Even with good planning and on-site inspection it is difficult to establish cost certainty and consequently cost contingencies will need to be incorporated. Fixed price contracts are likely to be unsuitable. Lump sum contracts are more appropriate where they are based on schedule of rates or quantities. When quoting for refurbishment work the contractual issues should be carefully checked and, if necessary, contractual experts consulted. Refurbishment schemes typically involve a high proportion of services which qualify as plant machinery for capital allowances. Expenditure that may be eligible for capital allowances for refurbished buildings includes that for the construction or acquisition of: space or water heating systems, powered systems of ventilation, air cooling or air purification, plus any ceiling or floor included in such systems lifts, hoists, escalators, moving walkways refrigeration or cooling equipment sound insulation requirements burglar alarm systems partition walls where removable and intended to be moved. BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 5

18 SECTION 1 INTRODUCTION Where alterations are carried out to facilitate installation of the new plant or machinery, the associated alteration work to the structure, such as the demolition of a wall or creation of a hole through a slab may be eligible for capital allowance. Capital allowances can potentially be claimed where old plant rooms are removed, risers and lift shafts are altered and where suspended ceilings and raised floors are used as a plenum for ventilation, thus making refurbishment more cost effective. Where repairs are carried out to HVAC plant they may be eligible for tax relief with the possibility that it may be incorporated within the profit and loss account. This implies that they are eligible for 100% deduction from profits for that year rather than the deduction spread over longer periods for capital allowances. Expert advice regarding tax issues should always be taken. There is increasing demand for Government to make greater concessions to encourage building refurbishment rather than demolition and creation of more brownfield sites, which are often considered unattractive for redevelopment. Options include extending capital allowances or allowing local authorities to reduce business rates on occupied refurbished properties or increase them on empty properties. In terms of the increase in letting value that can be obtained by refurbishment, a survey carried out on behalf of RICS Refurbishment in the office sector 1997/8 [2] suggested that a typical 1960/70s speculative office in a central prime site that had been refurbished comprehensively both internally and externally could have its letting value increased by 16-20% from 25/ft 2 ( 270/m 2 ) to 30/ft 2 ( 323/m 2 ). The variation in increase in letting value ranged from a net increase of 6% to a net increase of 30% depending upon geographic area. Such rental increase easily offsets the loss of rental income during refurbishment. Further, costs may be reduced by phased refurbishment (eg floor by floor) with increased rent from completed floors paying for further work. 6 Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

19 CHARACTERISTICS OF BUILDINGS SECTION 2 2 CHARACTERISTICS OF BUILDINGS OF DIFFERENT AGES AND THEIR IMPLICATIONS FOR REFURBISHMENT 2.1 OFFICE BUILDINGS The provision of building services refurbishment design options is much dependent upon the age of the original building. In the following sections the attributes of buildings of different ages are considered in general terms and their likely effect on building services refurbishment. A description of different construction techniques is given in Section Pre-World War II offices These buildings are likely to have high ceilings and a narrow floor plate. They have structural partitions, inflexible space and poor circulation routes. Buildings are likely to be naturally ventilated with space heating via a radiator system. Insulation levels are likely to be poor. Buildings may be listed. A typical refurbishment is likely to route services (power, heating and communications) around the perimeter. Additional cooling may be provided for meeting rooms and areas with high heat gains in the form of fan coil units or cassette type air conditioning units. Solar shading is likely to consist of internal or external blinds Late 1950s/1960s offices Buildings constructed in the late 1950s/1960s typically have a narrow floor plate, open plan layout, low floor-ceiling height, low floor loading, and are relatively lightweight. They will not have been designed with raised floors or suspended ceilings thus requiring routing of the services around the perimeter. Insulation levels are probably poor and single glazing is likely to have been employed. The addition of a raised floor to these buildings as part of a refurbishment causes problems with levels which may be overcome by the addition of ramps or steps and the raising of internal doors. Particular problem areas arise around lifts and stairwells. Clear duct and pipework routes may present a further difficulty, particularly where large ventilation ducts are required. This may be overcome to a certain extent by separating ventilation and cooling, perhaps through the use of fan coil units or chilled ceilings, in conjunction with natural ventilation or minimal mechanical ventilation rates to satisfy occupant requirements. In this way ductwork size is either minimised or eliminated. Where ductwork is required the use of several small ducts to supply localised air terminals rather than one large duct is a possible solution. The problems with these buildings are highlighted by the experience in the City of London during the boom of the 1980s. The growth in the use of IT ( Big Bang ) and associated power requirements, the perceived high air conditioning loads together with the increasing need for flexibility, led to many 1950s/1960s buildings being demolished as they no longer met the requirements of financial institutions. BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 7

20 SECTION 2 CHARACTERISTICS OF BUILDINGS s offices These buildings tend to have larger floor-to-ceiling height than 1960s buildings to allow routing of the services. Open plan layouts are deep in plan (typically 12 m or more) and suspended ceilings are used. Construction is typically lightweight particularly in terms of internal non-load bearing partitions, single glazing and poor insulation. Facades may allow a high degree of air infiltration. Fully glazed facades lead to high heat gains which are overcome by the use of increased supply air volumes or air conditioning in high specification offices. A typical refurbishment is likely to include complete replacement of services (intermediate) and possible structural alterations (major refurbishment) such as replacement of the facade s offices Early 1980s buildings were affected by the recession in 1982/83 which led to an emphasis on refurbishment rather than new build. However, the boom in the latter part of the 1980s led to the construction of many new buildings, often following the demolition of older buildings which were inappropriate for the growth in the use of IT and the associated air conditioning loads (see late 1950s/1960s). Letting agents became powerful during this period, setting the specifications for what was, and was not, lettable. They often set specifications for large office developments which subsequently fed into the British Council of Offices (BCO) Specification which became the norm for many buildings of the period. This represented the plateau for building power/cabling and air conditioning requirements (air conditioning design cooling loads for office IT equipment were typically taken as 45 W/m 2 (net floor area) as opposed to the more realistic 20 W/m 2 now specified). Consequently, many of the financial institution buildings constructed in the 1980s are now considered overserviced. A typical refurbishment for these buildings is likely to be cosmetic although intermediate refurbishments with plant replacement are set to increase due to the age of the services. Buildings with more demanding IT requirements have probably already undertaken several IT network refurbishments s offices The recession in the first half of the decade led to an excess of un-let office space both new and old, the quantity of old space increasing as leases originating in the 1960s and 1970s came to an end. The last part of the decade is characterised by the emergence of the UK economy from recession combined with the rising concern regarding environmental issues and the advent of sustainability. Combined with this, technological advances in computing and other office equipment have led to lower cooling loads. It is now recognised that some cooling systems were over-specified and that cooling requirements can be reevaluated. There may not be a need for full air-conditioning. There has been consequent recognition of a number of alternative cooling techniques capable of maintaining reasonably comfortable conditions in buildings with typical heat loads. These techniques include chilled 8 Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

21 CHARACTERISTICS OF BUILDINGS SECTION 2 ceilings, the use of fabric energy storage (passive cooling of exposed concrete ceilings at night), evaporative cooling as well as variable refrigerant volume (VRV) systems to provide localised cooling. The review of Part L of the Building Regulations (1998/9) is likely to include greater justification of full air conditioning in buildings. The increasing awareness of the benefits of solar shading has started to make a greater impact on heat gains. The decade has also been characterised by changes in the way of carrying out business - the growth of telephone based direct services, home working and the advent of hot desking. The arrival of the CDM Regulations has made provision for the mandatory recording of health and safety information relating to construction, maintenance, repair or demolition work on a structure throughout every phase of construction and at any time after the completion of the project. Tenants are becoming much more aware of building running/life-cycle costs (although those in prime location sites often choose to ignore these costs). New methods of building procurement are arising, such as through the Private Finance Initiative and life-long partnering, where contractors design, build, operate and maintain buildings for a specified lifetime. Buildings that are only five to ten years old require predominantly cosmetic refurbishments, perhaps brought about by reorganisation of departments within a building. The increasing use of IT and the need to replace outdated cabling systems to allow optimum use of the latest technology implies frequent upgrades and refurbishments Future offices This is covered in more detail in the third publication of this series: Refurbishment of concrete buildings: Designing now for future reuse [7]. It is expected that the IT revolution will continue to bring about further changes to the equipment on the desks. Structured cabling systems currently being installed seem likely to be adequate for tomorrow's needs. Flat screen technology is expected to make a large impact, potentially reducing heat loads and allowing greater occupant density due to reduced space requirements of flat screens. The maximum occupant density of existing buildings is dictated by the means of escape (often there are not enough staircases), the provision of toilets and the requirement to provide enough space for people to work productively. The current occupant density limit is about 1 person to every 5 or 6 m 2 although future building designs may reduce the space allowance. In the longer term, computer processing power may be removed from desks and reside in a central computer room. As wireless network connections and mobile telephone communications take off, then office arrangements will be eased, particularly if cableless power supplies such as photovoltaic powered devices can be used with flat screen technology. BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 9

22 SECTION 2 CHARACTERISTICS OF BUILDINGS Home working is expected to grow. The amount of time at home will depend on the type of work being undertaken, ranging from those that spend virtually all their time working from home to those who use it as a means of avoiding traffic congestion or as a means of completing work without the interruptions associated with office life. The growth will be accelerated by the greater number of self-employed professionals working from home, an extension of the growing trend of outsourcing. The office, for some, may become a place for training, meetings, social interaction, a place to receive new work assignments or to report on the progress of existing work. 2.2 OTHER BUILDINGS Shopping centres The large number of new shopping centres completed over the last ten years has forced refurbishment of the 1960s/70s shopping centres in order to win back customers. The growth of out-of-town shopping centres has particularly affected this, especially where a major retailer has moved from a large town centre site in favour of an out of town store. Refurbishment of a shopping centre might include addition of a roof to uncovered centres as well as cosmetic refurbishment (repainting, new floor, re-signage, help desks, etc). This introduces the requirement for other building services, notably fire/smoke control, as well as mechanical ventilation and possibly air conditioning. Sprinklers may also be added, together with new escalators and lifts. Multi-storey car parks are also an important part of the shopping centre refurbishment since many shoppers feel intimidated by them. Typically, soffits are painted a light colour, lighting is improved and signage replaced Housing/hotels Refurbishments of office buildings to private apartments, social housing etc are increasing in number. Particular attributes of office buildings include their availability, proximity to city centres and associated ease of access to both work and entertainment/leisure facilities. The recent realisation of the need to re-populate and revitalise city centre areas, which have been predominantly utilised for work only, has also encouraged refurbishments. Westminster Council is one example where both social and executive housing schemes have been encouraged. Another example is a 5500 m 2 scheme in Birmingham to create 68 flats [9]. Other schemes have led to refurbishments for student accommodation, for example, the refurbishment of four office blocks in the centre of Bristol by a developer and let on a fifteen year lease to the University of the West of England. However, another scheme at Roehampton Institute has done the reverse, converting student accommodation into a Learning Resource Centre due to the shortage of campus educational buildings. Other conversions have provided low cost hotel accommodation, such as the conversion of part of County Hall in London. 10 Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

23 CHARACTERISTICS OF BUILDINGS SECTION 2 Refurbishment of office space to housing or hotels is generally characterised by the need for additional drainage from each unit, often necessitating additional drainage pipes within risers. The provision of water and electrical services to each unit is easily facilitated by routing the services within the ceiling void, typically above a central corridor. The comparatively high floor to ceiling heights in offices makes this possible Serviced office space A small but growing part of the market is where existing office accommodation is refurbished and split to provide serviced office space. The term serviced offices can range from self-contained office suites with excellent services, to redundant office space, temporarily split by partitions and let on short term leases until the whole floor can be let [10]. It is expected that demand for serviced office space will rise due to the growth in small companies, although they are unlikely to provide the capital growth and long term security, typical of long lease holds, favoured by institutions. As an income-generating business, they may be more suited to property company portfolios, entrepreneurial service companies and joint ventures [9]. Examples include Farley Hall, Bracknell, and 30,000 m 2 of serviced office space developed in Manchester [9]. A more detailed listing is provided in An introduction to serviced offices [10]. 2.3 METHODS OF CONSTRUCTION It is not generally possible to determine from exterior building inspection the method of construction, ie. cast in situ, precast or a combination of the two. Unless records of the construction are available, which is unlikely, particularly for buildings constructed prior to the CDM Regulations, the construction method can only be determined with any certainty once the false ceilings and other finishes are removed. This section is intended to give the engineer an indication of some of the various forms of construction that might be encountered during refurbishment. For further background information on the historical use of concrete in buildings reference can be made to a special issue of the proceedings of the Institution of Civil Engineers [11] which is soon to be published as a book. Information on concrete problems, some of which are related to the method of construction, is given in Section In situ construction Stanley [12], 1979 gives brief highlights of the history of concrete. Those relevant to buildings are summarised here. The use of concrete as a building construction material has a long history dating back to ancient times. Modern-day concrete, however, first began its development in the 19 th century when the idea of reinforced concrete was first suggested in It was patented in 1854 by William Wilkinson, a builder from Newcastle, but was little used. Buildings constructed in concrete in the late 1800s were generally of mass in situ concrete and included dwellings, hotels and farm buildings. Some floor slabs, however, were constructed with reinforcement. BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 11

24 SECTION 2 CHARACTERISTICS OF BUILDINGS Structural concrete was introduced during the late 19 th /early 20 th century when pioneer François Hennébique further developed the design and construction of reinforced concrete and it began to be used more extensively. Industrial buildings, warehouses, dwellings and multistorey structures were constructed, with the first in situ RC frame structure built in Liverpool in Between the two world wars prestressed concrete was developed by Eugène Freyssinet and systems for pre- and post-tensioning concrete members have been available in the U.K. since the late 1950s, given momentum into the 1960s by the first code of practice CP115 for pre-stressed concrete. Some early examples of its use are described in The use of prestressed concrete in buildings [13]. However, the techniques were not used to any great extent until the building boom of the 1980s [14]. In general, in situ concrete buildings encountered nowadays will be reinforced. Some may also have prestressed members, particularly precast concrete for floors. Table 2 summarises the various RC frame and member types used since before the Second World War to the present day. Period Pre-WWII to early 1960s FRAME TYPES Type, description, design basis Portal frames (mainly for industrial buildings) Diagram Table 2 RC frame and member types Braced column frames Early 1960s Early 1970s Interior, exterior and corner columns treated differently. Lateral loads were taken into account Sway frame design Design for no sway 12 Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

25 CHARACTERISTICS OF BUILDINGS SECTION 2 SLAB TYPES Period Type, description, design basis Diagram Pre-WWII Monolithic beam and slab - single spanning (supported on two edges) - double spanning (supported on all edges), not well understood so little used. Flat slab (or mushroom floors) - supported by columns only Without dropped panel With dropped panel Column Head Column Column Head Column Hollow tile slab ribbed slab with hollow clay tiles to simplify shuttering. More economical if span > 10 ft. Post WWII Early 1960s Hollow clay tiles Generally as pre-war, but double spanning slabs better understood and thus more common. Hollow tile slabs becoming known as hollow clay-tile slabs. In addition to the older forms the following also began to be used: Ribbed slabs, ie. contiguous T beams. See note 1. Cantilevered structural form THROATING BEAM Early 1970s Slabs began to be used over continuous as well as single spans In addition to the older forms the following also began to be used: Waffle slabs with and without beams. Waffle slabs with integral beams. Ribbed slabs with bad beams and integral beams. Solid slabs with band beams. Post-tensioned solid and ribbed slabs. Precast and composite slabs with beams. Slab types Note 1: Permanent wood-wool formwork was used to form ribbed slabs. Because of the porous nature of the material, grout could be lost from the concrete surrounding the reinforcing bars, leading to a reduction in bond and a risk of corrosion. As the formwork was left in place, there was no opportunity to inspect the concrete at the time of construction. This is an area of uncertainty which can only be resolved by removing the wood-wool slabs in critical locations. BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 13

26 SECTION 2 CHARACTERISTICS OF BUILDINGS Period Pre-WWII BEAM TYPES Type, description, design basis Rectangular beam reinforced in tension zone only Diagram Rectangular beam reinforced in tension and compression zones T beam L beam Post WWII Early 1950s Irregular cross sections accommodated in design guidance Some I beams began to be used Prestressed RC beams introduced but little used I beams commonly used 14 Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

27 CHARACTERISTICS OF BUILDINGS SECTION 2 COLUMN TYPES Period Type, description, design basis Diagram Pre- WWII Square or rectangular sections Various reinforcement binding: Helically bound for circular sections. Post WWII Early 1970s Slender columns Slender columns no longer used but long columns used. Plastic theory introduced. Irregular sections used. Slender columns re-introduced. Period Pre-WWII Early 1950s Early 1960s WALL TYPES Type, description, design basis No design guidance for load bearing walls, so walls generally non-load bearing, ie. curtain walls. Load bearing walls designed as long columns. British Standards introduced for load bearing wall design Precast construction Precast concrete for major structural purposes started in the late 19 th /early 20 th century [15], and much was used in the earliest days of reinforced concrete. During the 1960s and 1970s, precast units were extensively used for the whole of the structure, in a number of different building systems, or in conjunction with in situ concrete. A very wide range of industrialised building systems was available at the time [16,17]. Such systems were based either on concrete frames consisting of precast structural members (columns and beams), or large precast concrete panels (eg. the Bison Wall Frame introduced in the late 1960s) forming structural walls and floors, the latter being used largely for multi-storey residential buildings, but also for office buildings and hotels. The National Building Frame was introduced in 1965 and was used for industrialised concrete frame buildings up to six storeys high. The idea behind the system was to standardise components using a minimal number of precast moulds, thus simplifying construction. The system was designed in accordance with the principles proposed by the Ministry of Public Buildings and Works and the concrete design code of the day [18]. Frames comprised five precast concrete elements: columns, spine beams, edge beams, gable beams and double T panels for floors and roofs. Columns were generally set out on a 2 ft (600 mm) grid, although 3 ft (900 mm) grids were also used, with a maximum span of 42 ft (12.6 m). Column sizes were 8 in x 8 in, 8 in x 12 in and 12 in x BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 15

28 SECTION 2 CHARACTERISTICS OF BUILDINGS 12 in ( mm), and tended to be the full building height. Beams had a structural depth of 20 in (500 mm) and a width of 8 in. Double T floor units had structural depths of 12 in, 16 in (400 mm) and 20 in with ribs at 2 ft spacing displaced 1 ft (300 mm) from columns. Floor-toceiling heights were from 8 ft (2.4 m) upwards in increments of 1 ft. Ducting and access for services could be cast into the units or cut in situ. The system was a sound solution but was controlled by an association of licensees who were the only parties allowed to use the system, thus leading to the development of The Public Building Frame. The Public Building Frame was introduced in 1966 [19] and was developed along the lines of The National Building Frame by the Ministry of Public Buildings and Works. It consisted of a limited number of standard units, with the aim of simplifying the construction of buildings of up to 12 storeys, though it was used for higher structures. Column layout was on a 2 ft or 3 ft module (600 mm or 900 mm) with a maximum spacing of 40 ft (12 m) for offices. The standard depth of the floor zone was 12 in or 24 in (300 mm or 600 mm), with the preferred floor-to-floor heights varying in 1 ft increments (300 mm). Floors were formed from precast box sections, double T units, beam and block or prestressed plank units, all with a structural screed of at least 2 in (50 mm). Unlike present day precast frame systems, the columns were storey height and the beams were continuous through the beam-column connection, with beam-beam connections at mid-span. Awkward areas were, however, constructed in situ. Access for services between floors was generally provided by cutting appropriate holes in the precast floor units. Unlike The National Building Frame, the Public Building Frame was available to any designer. Further developments to The Public Building Frame were to use the previously devised standard components and apply them to bespoke solutions. In Lift Slab or similar buildings, the reinforced concrete slabs are all cast in situ at ground level and are then lifted up the precast columns and anchored in their final positions. As far as individual units are concerned, beam and pot or beam and block floors have been available for many years, and are still widely used for short spans, particularly in domestic situations. Prestressed hollow core units similarly have a long history. Double T units were introduced for long span floors in the mid-1960s as described previously. With the use of The National Building Frame and the Public Building Frame, a plethora of precast concrete buildings was realised in a short time period. This trend was short-lived, however, due to the capital investment necessary for prefabrication factories. Moreover, the social consequences of these buildings were unfortunate for large panel systems. In situ concrete building construction was thus reverted to in the 1970s and 1980s. Today the precast industry has only about 3-4% of the concrete building frame market, but the full cycle is beginning to be completed following the recession during the early 1990s which has led to a national drive for efficiency and consequently the rationalisation of elements in the form of precast members. But this time details of quality and aesthetics are being given more attention [20]. 16 Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

29 CONDITION SURVEYS SECTION 3 3 CONDITION SURVEYS PRIOR TO REFURBISHMENT Before any refurbishment can be undertaken, condition surveys of the existing building structure, its services and its finishes must be carried out to assess the viability of re-use. This should particularly consider Health and Safety aspects, the requirements of CDM Regulations and other legislation, see Appendix A. The essential aspects of building services and the structural surveys are discussed in Sections 3.1 and 3.2 respectively, whilst more minor, but nevertheless cost-contributory aspects that should be inspected are listed below: external decoration paintwork rendering roof coverings repairs to asphalt or felt inspection of parapets, gutters and rainwater outlets external doors and windows and their frames sound insulation of internal walls demountability of internal walls internal fixings and finishes screed thickness decor ironmongery doors partitions signage sanitary facilities security alarms. 3.1 ASSESSING THE CONDITION OF EXISTING BUILDING SERVICES The decision to refurbish or renew electrical and mechanical services purely on the basis of their condition is difficult. Up to a point it makes sense to tolerate reduced standards of heating, air conditioning, lighting etc, provided Health and Safety and environmental requirements are met. However, the risk of failure of systems increases with age and consequent deviations in air quality and thermal comfort levels may reduce occupant productivity. The cost of breakdown may also incur higher costs than replacement at an earlier opportunity and the falling standards of the services may also reflect on the building's asset value. Typical life expectancy of various building services are given in Table 3. Refurbishment or renewal of the building services normally takes place as part of a wider scheme of complete building refurbishment, often in conjunction with a lease renewal, although occasionally refurbishment of the main building services plant only is undertaken. BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 17

30 SECTION 3 CONDITION SURVEYS Table 3 Life factors for M&E plant and systems [21] Equipment item Typical economic life (years) Boiler plant Shell and tube boilers (medium and low pressure) 15 to 20 Water tube boilers (medium and low pressure) 15 to 20 Cast iron sectional boilers (medium and low pressure) 15 to 25 Steel boilers (medium and low pressure) 15 to 20 Condensing boilers (medium and low pressure) 15 to 20 Refrigeration plant Reciprocating chiller 15 to 20 Screw chiller 15 to 25 Fans Centrifugal and axial 15 to 20 Propeller 10 to 15 Pumps Pumps (base mounted) 20 to 25 Pumps (pipework mounted) 15 to 20 Ductwork Ductwork (galvanised) 25 to 35 Ductwork (plastic ) 35 to 40 Ductwork (flexible circular) 20 to 30 Terminal units Fan coil units 12 to 15 Terminal reheat units 20 to 25 VAV (box type) 15 to 20 Chilled ceiling panels and beams 20 to 25 VRV units 15 to 20 Radiators (steel) 10 to 15 Radiators (cast iron) 20 to 25 Pipework Open pipework (steel) 25 to 30 Closed pipework (steel) 30 to 50 Open pipework (copper) 30 to 40 Closed pipework (copper) 40 to 50 Open pipework (steel galvanised) 30 to 35 Closed pipework (steel galvanised) 35 to 45 Insulation Insulation (blanket type) 15 to 20 Insulation (moulded) 15 to 20 Electrical Mains cables (permanent installations) 20 to 30 Switchgear and distribution equipment 20 to 25 Lighting installations (internal) 20 to 25 Motor control centres 20 to 25 Building management and controls Supervisory computer 5 to 10 Intelligent outstations 5 to 15 Valve/damper actuators 10 to 15 Control valves and dampers 15 to 20 Sensors 3 to 10 Hardwiring between devices 20 to 30 Fire alarms (electrical) 20 to 25 In assessing whether or not to re-use the building services, detailed surveys of mechanical and electrical systems should be undertaken, together with consideration of the building fabric and structure, where these are affected by the changes. 18 Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

31 CONDITION SURVEYS SECTION 3 Table 4 Checklist of building services issues Lighting Heating DHW Ventilation Air conditioning Pumps Terminal units - heating Terminal units - ventilation Terminal units - cooling Fabric Electrical distribution Control Zoning Zoning, optimum start, compensation timeclock, capacity control Zoning, capacity control Zoning, capacity control Local + remote, zoning Local + remote, zoning Local + remote, zoning Power/ control cabling Table 4 provides a list of services likely to be found in a building together with a number of aspects that should be checked as part of a condition survey. The shaded cells are categories that are not applicable to a particular service. The text in italics is a prompt for issues to be considered. Efficiency/ running cost Heat gains minimised? Refrigerant used? Optimum sizing Shading, glazing, air leakage Pipework Ductwork Distribution system Insulation Expected life Reliability Aesthetic value Ease of operation Control system Zoning Cable Panels Fire system Zoning Cable Panels Security system Zoning Cable Panels Lifts Toilets Communications / IT Cable Cleanliness/ corrosion Panels Panels Suitable for reuse? Where it is obvious that services are time-expired and renewal is required the survey will focus on location of plant rooms, space available for distribution and suitability of alternative plant systems. The engineer will assess all relevant factors and derive the most cost effective solution. Where it is not clear whether the existing services are to be kept or replaced there are many considerations to be made. The principal factors are outlined below Automatic control systems These can be split into two types, those that are standalone and those that communicate via a network or bus. Networked systems are likely to form part of a Building Management System (BMS). These products have developed significantly over the last five years, offering a greater degree of functionality, including improved management information BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 19

32 SECTION 3 CONDITION SURVEYS and ease of operation. Where building services plant is being renewed, it is advisable to replace BMS products over five years old as part of the refurbishment. Where standalone controls are being used, perhaps to control boiler or ventilation plant, it is recommended that the controls are upgraded if the plant is being changed or if networked controls are required. Where the plant and controls function satisfactorily and there is no requirement for central monitoring, there is likely to be little benefit in changing the control system. However, checks should be made to ensure that functions such as optimum start, compensation, frost protection, etc are incorporated and that time-clock and other functions, as far as they can be tested, operate satisfactorily. The minimum control requirements for boilers are given in section Fire alarm systems Where fire alarm systems are to be refurbished it is essential that they meet the relevant British Standards which include: BS 5839: (Parts 1 to 8): Fire detection and alarm systems for buildings [22] BS 5445: (Parts 1 to 11): Components of automatic fire detection systems (some parts are equivalent to EN54) [23] BS EN54: (Parts 1 to 9) Fire detection and fire alarm systems [24] BS 7807: Code of practice for: Design, installation and servicing of integrated systems incorporating fire detection and alarm systems and/or other security systems for buildings other than dwellings [25]. Note that some of the above standards comprise part numbers, some of which are withdrawn, under revision, drafts or under development. The principal aspects to consider revolve around insurance company and Building Control/Fire Prevention Officer requirements. They include ensuring that the existing system will function satisfactorily under both fire and normal day to day conditions. Other considerations relate to ensuring the correct signage for escape routes, and adequate means of escape, smoke control requirements, etc. Checks should be undertaken to ensure the fire alarm system will meet the requirements of the tests detailed in BS 5839:Part 1:1988. This relates to tests and checks including: sounders, detectors, power supply unit, communications, control panel, wiring, documentation. System replacement should be undertaken if there is doubt about the ability of the fire alarm system to meet the requirements before the next likely building refurbishment Electrical installation Life expectancy of power cables varies between twenty and forty years, depending upon the cable loading throughout its life and its physical condition. Electrical cabling installed in buildings in the 1970s tended to be oversized, implying that the cable has run much cooler and consequently has lasted longer. These cables are likely to be suitable for reuse where space and power requirements have not extensively changed. Cable sizing depends on geographical area to a certain extent - buildings in London are likely to have a reasonable amount of spare 20 Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

33 CONDITION SURVEYS SECTION 3 cable capacity whereas regional cities may have been designed more tightly. Building usage will also affect the loads applied to cables. When assessing the efficacy of cable re-use considerations include: the condition of the insulation (brittle or broken insulation, perhaps due to rodent attack, should be replaced due to fire risk) satisfactory electrical insulation and earth continuity tests the ability of cabling to meet the layout and power load requirements in the refurbished building any allowance for increased future loads availability of satisfactory containment systems satisfactory bonding and earthing - the requirements have changed significantly with the introduction of BS 7671:1992 Requirements for electrical installations: IEE Wiring Regulations [26] the possible generation of harmonic load currents from computer equipment, variable speed drives and fluorescent lighting ballasts, etc. Harmonics may lead to voltage distortion, overheating of neutrals and other problems. Recent recommendations [27,28] suggest sizing the neutral conductor to 200% of each phase conductor. The inspection of the electrical installation should meet the requirements of BS 7671:1992. Requirements for electrical installations: IEE Wiring Regulations [26]. A recent unpublished survey referred to in Electrical design - a good practice guide [28] showed that, on average, the electrical infrastructure of buildings is refurbished every nine years with approximately 37% of the installation being replaced. Electrical panels are the most likely components to be re-used. They may require extension to cater for additional loads (where supply cable capacity allows). Distribution boards are likely to be changed, normally as part of a change of subcircuits for a tenant, such as a change of lighting or the installation of new floor outlets, but also to upgrade rewireable fuses to miniature circuit breakers (mcbs) Lighting installation Lighting for workstations and/or display screen equipment should meet the requirements of the Health and Safety (Display Screen Equipment) Regulations and the recommendations of CIBSE Code for interior lighting [29]. The Regulations require the avoidance of glare and troublesome reflections in all existing workstations from 1 January If refurbishment is being undertaken existing light levels (illuminance) should be checked to ensure sufficient illuminance. This should be measured in accordance with the procedure in CIBSE Code for interior lighting. The potential for greater use of natural light should be considered [30] as well as the method of switching artificial BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 21

34 SECTION 3 CONDITION SURVEYS lights or the type of lighting control system installed which should operate so as to prevent unnecessary energy wastage. The lamp type should be checked to ensure that it is not an inefficient product. Tungsten (GLS) lamps should be replaced with compact fluorescent lamps (CFL) as a matter of course. Tubular fluorescent lamps such as 38 mm (T12) tubes should be replaced with newer 26 mm (T8) or 16 mm (T5) lamps, perhaps as part of on-going maintenance if budgets are restricted. T8 tubes give approximately 10% energy savings for the same capital cost of the T12 tubes. T5 tubes offer an additional 5% saving compared to the T8 tube. Alternatively, retrofitting of luminaires with high frequency ballasts should be considered. These offer 15-20% savings over conventional ballasts. One method for assessing the efficiency of installed systems given in Energy management and good lighting practices [31] is as follows: a) measure the area in m 2 b) assess installed lighting load in watts. (Number of lamp points x lamp wattage; add 12% for control gear for fluorescent and discharge lamp installations.) c) divide b) by a) to obtain installed load in W/m 2 d) measure average illuminance (lux). A commercial installation with modern efficient equipment will require an installed load of approximately W/m 2 for each 100 lux illuminance. If the check shows a higher electrical load then a more detailed investigation is advised Boiler system/domestic hot water systems Assessing the remaining useful life of boilers is difficult. Generally they are replaced due to their age, perhaps when they have passed twenty years. Replacement is normally justified by the increasing risk of failure together with the higher efficiency (see Figure 1) achievable with modern boilers and better control systems available. The Boiler (Efficiency) Regulations 1993 require that all new boilers meet efficiency standards (see Appendix A1.3.5). Building Regulations: Part L [32] require the provision of automatic controls for boilers over 100 kw as follows (other requirements apply to boilers of less than 100 kw): optimised time controls sequence control of multiple boilers space temperature control weather compensation where domestic hot water is supplied a thermostat to control domestic hot water storage temperature. 22 Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

35 CONDITION SURVEYS SECTION 3 Figure 1 Part load efficiencies of boilers [33] The renewal is likely to be further justified by installation of a correctly sized boiler rather than the existing boiler which is likely to be oversized [34]. This is all the more important where fabric insulation improvements are being made or a heat recovery scheme is to be implemented. Buildings with a large boiler may be better served by adding a small boiler for summer conditions. This might be a condensing boiler or high efficiency boiler, either of which should act as lead boiler at all times due to the higher operating efficiency. Heating system option appraisal [33] gives one basic method of heating system selection. Large sites or building complexes should consider the decentralisation of boiler plant to minimise distribution losses. Further benefits are likely to arise through the replacement of large central boilers with modular boilers to meet part loads more efficiently. Direct fired water heaters will help to further reduce distribution losses and allow the shut down of boiler plant in the summer Ventilation systems Ventilation air may be provided mechanically, via fan systems, or naturally, typically using openable windows, vents, etc. There are a number of ways of assessing the effectiveness of a ventilation system including: measuring CO 2 concentration in the space when it is at maximum occupancy (levels in excess of 1000 ppm indicate inadequate ventilation) measuring ductwork supply air velocity and fresh air inlet velocity as an indication of overall air volumes entering the space smoke visualisation techniques as an indication of air flow distribution within a space tracer gas techniques where the decay of a gas source such as sulphur hexafluoride is monitored as an indication of ventilation rate. BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 23

36 SECTION 3 CONDITION SURVEYS Assessment of the existing ventilation system should include checks of: environmental conditions in the ventilated space (temperature, stuffiness, air quality, odours etc) the operation and control of any dampers the condition of the fan motor, pulleys, fan, filters, as well as heating, cooling and humidification devices (ductwork is considered in section ) the potential for retrofitting a more energy efficient air flow control device (for example, replace guide vanes and throttling dampers with variable speed drives) possible oversizing of the installed ventilation system [35] the operation of any timeclocks. The main energy saving measures relate to: effective matching of supply air flow rates to actual requirements heat recovery from extract air recirculation of extract air use of variable speed drives improved control systems (improved zoning, use of free cooling, holiday programming on timeclock) Cooling systems Cooling systems may be classified as central or localised systems: central systems carry out cooling in a central plant room and distribute cooled fluid distributed to the point of use localised systems, where there is one unit per zone, such as variable refrigerant volume units. Central chiller plant may be overhauled or completely renewed as part of a refurbishment. The viability of overhauling will depend on the chiller age and required cooling capacity. Overhaul will include cleaning of all heat exchange surfaces and upgrading of in-built chiller controls. Modern chillers are generally more efficient than older ones, particularly at part loads, so refurbishment of an old chiller may not be economic. Other considerations relate to the type of refrigerant used by existing systems in light of the phasing out of CFCs and HCFCs - see Appendix A, section A The principal standard relating to cooling systems is BS 4434: 1995 [36]. As part of the assessment of cooling systems, consideration must be given to the minimisation of heat gains in the space, particularly by the use of solar shading, low energy lighting and by the positioning of equipment with high heat gains in dedicated areas. The leakiness of the facade must also be considered, as the installation of energy efficient cooling equipment in a leaky building renders it less effective. In order to increase lettable floor area it may be feasible to relocate chiller plant from an enclosed plantroom to an external position. Alternatively, a complete change of the method of cooling provision away from central plant may be viable if cooling is only required in localised areas. 24 Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

37 CONDITION SURVEYS SECTION Lifts and escalators Lifts typically have a life of 10 to 20 years before the major moving parts have to be replaced due to wear and tear, while some parts remain mechanically sound for 50 years, or more, if well maintained [37]. If the lift service is adequate, limited refurbishment is possible. This may include updating the control system to improve operating efficiency, refurbishment or replacement of the existing lift motors, replacement of ropes and cosmetic refurbishment. Alternatively, rebuilding of the lift cars including relining of the walls, decorative ceiling and lights, new landing doors, etc may be required. The main legislation affecting lifts are The Lifts Regulations (see Appendix A, Section A1.3.3) and BS 5655: Parts 1 to 14 (Parts 1 and 2 implement EN81). Note should be particularly made of Part 11: 1989: Recommendations for the installation of new, and the modernisation of, electric lifts in existing buildings, and Part 12 of a similar title, but applicable to hydraulic lifts. Typical requirements include request of a minimum depth of lift well, provision of an access ladder to the lift pit, reduced loading of the car, need for replacement wiring and requirement for fire rated landing doors. Refurbished escalators should endeavour to meet the standard given in BS EN115 [38], although it is not compulsory, as well as HSE Guidance Notes PM34: Safety in the use of escalators, and PM45: Escalators: Periodic thorough examination. Particular aspects relate to the lighting level at entry and exit points, the ease of passage to the entry point and away from the exit, the gaps between equipment items with a view to assessing the risk of entrapment, the operation of safety devices Pipework Whilst main plant is typically replaced at the end of the year building lease cycle the existing pipework may still be functional. Greater use of copper pipe has given increased life compared to galvanised pipework, which may wear away the galvanised coating over a long period, leading to rusting and subsequent deposits in the water. Further, use of regular water treatment and effective means of keeping air out of systems has also led to extended pipework life. Vertical pipework in risers is likely to be in a more sound state than horizontal pipework, particularly that found at the bottom of a building such as in a basement, which is more prone to rotting and where deposits will have collected. Hot water piping in areas with poor water conditions is a prime candidate for replacement due to corrosion, together with vent piping and roof surface water drainage pipe which are exposed to atmosphere with the moist air consequently promoting corrosion. External inspection of pipework for corrosion and leaks, especially around welds, will determine the requirement for replacement without any further consideration. If external surfaces and connections appear satisfactory, measurements of flow and pressure conditions should be undertaken as an indication of blockage. Cutting out pipe samples for investigation of deposit build up on interior walls will provide the best diagnosis of the pipe condition. BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 25

38 SECTION 3 CONDITION SURVEYS Inspection of pipework must also consider the condition and provision of satisfactory supporting structures as well as the presence of redundant pipework, which should be isolated or removed. The condition, thickness and extent of existing insulation should be noted (particularly the presence of asbestos), including pipework runs outside of the building or through unconditioned areas. Flanges, valves etc must also be fully insulated. Consideration should be given to future use of the pipework. Improved insulation of fabric may render heating pipes (and terminal units) oversized. One way around this is to use a lower flow temperature, making the application of condensing boilers ideal Ductwork Ductwork can often be re-used subject to satisfactory cleanliness. The definition of clean may generally be taken as visually clean, but will depend on individual circumstances. Ventilation system hygiene [39] states that Health and Safety inspectors expect regular inspection of all ventilation systems to enclosed spaces and that appropriate logs will be kept. Any existing logs must therefore be consulted. The main considerations for re-use relate to whether the method of ventilation of the space is to change as part of the refurbishment and any requirement for new layouts or re-zoning. Where a VAV system is being removed, the ductwork is likely to be too big for re-use. Where induction systems are being removed, the old ductwork, especially in risers, is often suitable for re-use. Similarly, toilet extract system ductwork can often be re-used providing toilets are not being rationalised to improve net lettable area. Supply and extract ductwork should be inspected for air leaks and corrosion as well as the condition and extent of any insulation. Flow regulating devices must be inspected to confirm their functionality. Any requirement to add additional ductwork should consider the effect on flow rates on other parts of the system Facade (windows, air tightness, insulation) The decision to replace windows and glazing will depend upon three aspects: the condition of existing frames and glazing the need to improve the aesthetics of the facade the need to improve solar control. Inspection of existing windows should be undertaken to determine the condition of frames and glazing. Cracked, twisted and broken frames should be replaced, as should any cracked glazing. The remaining life of the window frames should be considered to assess if they will remain functional until the next major refurbishment, and, indeed, their aesthetic condition should be considered as this may affect the ability of the building to be let, as well as the rental value. 26 Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

39 CONDITION SURVEYS SECTION 3 Where a major refurbishment is being undertaken the incorporation of solar control is likely to form an important part of the new solution. Consideration of the ability of any existing solar control techniques to provide the heat gain reduction required should be made, as well as whether they are aesthetically acceptable for the new scheme. Assessment of the building fabric should include an assessment of the air-tightness of the facade. Uncontrolled (adventitious) ventilation significantly increases energy use, both for space heating and where the space is air conditioned. The facade should be inspected to establish the extent of gaps between windows and walls, between floors, ceiling and walls as well as at the point where service pipes and ducts enter the conditioned space. Lift and service shafts should also be inspected to establish the extent of sealing. Pressure testing of the building should be carried out to provide definitive data where doubt exists as to the building air tightness. The inclusion of a smoke test as part of this will provide visual indication of air leakage paths and determine remedial works required. Insulation levels should be checked. These not only help to keep heat in but also help to keep heat out in summer. Where facades are replaced they are not currently required to meet the insulation requirements of the latest Building Regulations. However, it is good practice to carry out refurbishment to meet latest Building Regulations. Where structural cladding is replaced then this must meet current Health and Safety requirements including Building Regulations, CDM Regulations etc, as must any product where safety may be compromised, for example replacement glazing. Where partial replacement of facades is carried out, the retained part will ideally have the insulation upgraded. Where insulation levels are poor, it should be remembered that poor insulation may lead to radiative cold spots which could prove uncomfortable to the occupants. Another consideration is where heating systems are being replaced. Improved insulation may reduce the size of boiler plant required thus helping to offset the cost of improved insulation. 3.2 ASSESSING THE CONDITION OF THE EXISTING STRUCTURE Before carrying out any significant refurbishment it is important that at least desk top and visual surveys of the concrete structure are carried out to determine its form, method of construction and general condition. Whether the structure contains prestressed, and particularly posttensioned, concrete elements will impact on the ability and financial feasibility of carrying out structural modifications that may be required to accommodate new services. A pre-planned condition assessment is usually necessary because the majority of the structure will not be visible without the removal of false ceilings, raised floors, internal and external cladding, etc. The findings of the structural assessment can impact heavily on the costs for refurbishment since it is essential that the structure will continue to function satisfactorily without significant maintenance until the next planned refurbishment. The level of inspection and assessment required will depend on the level of refurbishment being planned. For BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 27

40 SECTION 3 CONDITION SURVEYS example, if the building is to be completely refurbished, involving stripping back to the bare frame, a full inspection and at least an additional 25 year life expectancy (without unplanned maintenance) would be required of the structure, while for a minor/cosmetic refurbishment a visual inspection and a further five year life expectancy would be adequate. Structural assessment should be carried out to the following guidelines: traditional buildings [40] - See Section engineered structures I Struct. E Report Appraisal of existing structures [41] Subsoil and foundation conditions As a minimum for a major or complete refurbishment, desk-top studies into the condition of the ground supporting a building should be carried out. Many 1960s and 1970s buildings have been constructed on contaminated land and property buyers are particularly concerned about this issue. The I Struct. E report Appraisal of existing structures [41] gives guidance on this subject. BRE Digest 366 [42] also suggests that contact is made with the local building control authority who can advise on local building practice as well as geotechnical conditions. Various non-destructive techniques are available to determine the extent and condition of buried foundations [43]. If they are found to be deficient, some strengthening work will have to be carried out. Similarly if there are any signs of differential settlement between parts of the existing building, remedial work may be required. The effect of ground water levels should also be considered. Problems with the foundations are unlikely to be a great concern except for major refurbishments where they must be checked as a matter of professional liability, particularly if they involve an increase in loading on foundations. It should be stressed that any work carried out to the foundations will often be particularly problematic and hence a very detailed assessment of the situation should be carried out before any work is undertaken. Section gives options for foundation strengthening Reinforcement corrosion All exposed external concrete surfaces should be inspected for signs of reinforcement corrosion. Where possible, cladding should be removed in a few representative locations so that the main frame of the building may be inspected. As far as possible, internal surfaces should be inspected, particularly in areas that could be wetted, for example from leaking roofs, kitchens, toilets, etc. Inspection will require the local removal of carpets, raised floors and ceiling tiles, etc. The visual signs of reinforcement corrosion are: cracks along the lines of reinforcing bars rust staining local spalling. 28 Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

41 CONDITION SURVEYS SECTION 3 If corrosion is identified, it is important that its significance and cause are determined. In particular, is it a local problem caused by a single bar being displaced, or is it a more general problem due to low covers or sub-standard concrete? Any local damage that is identified should be repaired using a proprietary system. If the corrosion is more general, more radical steps may be necessary, such as realkalisation of the concrete and the application of a corrosion inhibitor (see Section 6.1). The risk of serious corrosion problems in building structures is, however, low and is more likely in major civil engineering structures subject to more aggressive environments. Consideration should be given to the application of a weatherproofing surface coating to exposed surfaces, which will improve the long-term durability of the structure as well as enhancing its appearance Concrete condition It is important that the condition of the concrete itself is such that it will not have long term problems. Particular areas of concern include: ASR (alkali silica reaction): If the building is located in a region in which ASR is known to occur, the surface of the concrete should be inspected for the characteristic cracking and any appropriate tests carried out (see Concrete Society Report 50 [44] ). It is unlikely that a building with significant ASR will be suitable for a major refurbishment because of poor appearance, although it is rare that ASR affects structural capacity. ASR would, however, be more likely to occur in car parks or other areas that are susceptible to moisture. If a structure is found to suffer from ASR its structural integrity should be checked [45]. HAC (high alumina cement) was used in some precast beams in the 1960s and 1970s. While the material achieved high early strength, and hence was very suitable for precasting applications, it tended to lose strength in the long term. Thus the strength of any members must be determined on the basis of the final or fully converted strength of the HAC concrete. Because of the structural failures that occurred (albeit in limited numbers) in the early 1970s, HAC is of particular concern to some building owners. The failures led to its withdrawal as a structural material in However, many floor units made with HAC remain in service. If such units were made under properly controlled conditions and used in dry environments, their residual strength has usually been found to be adequate [46]. Recommendations for the assessment of HAC concrete are given in BRE Digest 392 [47]. The process of reappraisal of the load-carrying capacity of the structure is discussed in Section Structural capacity. BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 29

42 SECTION 3 CONDITION SURVEYS Carbonation depth: In exposed, humid conditions the depth of carbonation should be assessed, in relation to the depth of cover to the reinforcement, to determine the risk of corrosion. If carbonation is well advanced and the relative humidity is near the optimum for carbonation to occur (around 65%), consideration should be given to treatment, such as the application of a corrosion inhibitor to the surface. Chloride ingress: Where there may be the risk of the building being subjected to chlorides, such as de-icing salts from neighbouring roads or spray in a coastal situation, the depth of chloride penetration should be determined in exposed parts of the structure, again to assess the risk of reinforcement corrosion. An additional source of chlorides in the concrete may be from calcium chloride, which was used as an accelerator in the 1960s before it was realised that its use could lead to reinforcement corrosion. The use of accelerators containing high levels of chlorides ceased in In both cases it will be necessary to prevent corrosion of the reinforcement, for example by the application of a corrosion inhibitor to the surface of the concrete. In addition there are techniques available for the removal of chlorides. The majority of applications have been for bridges but they have also been used for buildings [48]. Freeze-thaw damage: exposed areas should be inspected for evidence of any damage. Note, however, that freeze-thaw damage is unlikely to occur in the southern part of the UK. Local areas of poor compaction: Almost any structure will have some areas of poor compaction, honeycombing, grout leakage [49], etc. Local patch repairs should be carried out while areas of concrete are exposed so that they do not lead to possible problems in the future. Attention should be paid to any repairs that may have been carried out in the past. Their condition should be checked visually and by tapping with a hammer, and if there is any deterioration, such as cracking or delamination, the repair should be removed and replaced Structural problems The structure should be inspected for any signs of distress due to overloading or movements, such as differential settlement. Overloading will show as flexural and/or shear cracks wider than about 0.3 mm. Cracks less than 0.3 mm wide are generally not structural, although judgement by an expert needs to be exercised. Movements will lead to patterns of cracking other than those due to normal loading. For example, early thermal movements may have led to cracks right through a member rather than flexural cracks which extend, at most, from the tension face to the neutral axis. When movement cracks are identified, it is important that the cause is determined to assess whether the crack is still moving. All static cracks which are moisture susceptible or greater than 0.3 mm wide, such as those due to early thermal movements, 30 Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

43 CONDITION SURVEYS SECTION 3 should be routed out and infilled with grout. Cracks less than 0.3 mm wide may be left provided they are not subjected to moisture. When cracks are still moving, it will be necessary to eliminate the cause of the movement where possible or to ensure that the cracks are protected using an elastic filler to prevent corrosion of the reinforcement. The Concrete Society Technical Report No. 22 [50] can be used to identify structural and non-structural cracks. Techniques for structural repair and strengthening are described in Chapter Structural capacity If it is suspected that the structure is under-strength or the applied loads are to be increased significantly, the strength of the structure should be reassessed in line with the Institution of Structural Engineers report Appraisal of existing structures [41]. It is important to bear in mind that the structure will have been designed in accordance with the codes that were current at the time. Significant changes in the requirements, both for the design of the structure and the applied loadings, have taken place over the years. The design codes for reinforced concrete were as shown in Table 5. Table 5 Historic RC design codes [51,52,53] Period RC Design Code RIBA Report [51] London County Council Regulations DSIR Code [52] London County Council Regulations Building Industries National Council Code CP 114 for reinforced concrete CP 115 for prestressed concrete CP 116 for precast concrete CP Present BS 8110 [53] Table 6 Historic codes for design loads Invariably there would have been some overlap of these at each transition. Codes for design loads have also developed over the years. Table 6 gives design floor loadings for offices throughout the 20 th century: Year Code Imposed Load (kn/m 2 ) Partition Load (kn/m 2 ) 1909 London County Council (General Power) Act 1932 BS for upper floors for entrance floor 1944 CP3 Chapter V (not mandatory) PSA recommendation BS 6399 (Part 1) 2.5 minimum 4.0 for corridors, etc 1.0 BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 31

44 SECTION 3 CONDITION SURVEYS BS 6399 has been further developed since 1984 and now includes: Part 1 Dead and imposed loads 1984 Part 3 Imposed roof loads 1988 Part 2 Wind loads 1995 A code is a self-contained unit which relates to the loadings that are current at the time. It may be dangerous to consider parts of a code in isolation or to mix parts from current and previous codes. Notwithstanding the above, the loadings typically adopted from the 1960s to the present day for application to all office areas are 4.0 kn/m 2 imposed load and 1.0 kn/m 2 partition loading [54]. Some investors in buildings may insist on the use of imposed loads of 4.0 kn/m 2 throughout for the extra assurance of structural safety. Multi-storey buildings can have their imposed design loads reduced due to the probability that not every square metre of office will receive the full load simultaneously. BS 6399 specifies how the imposed loading can be reduced and Austin [54] recommends reductions on foundation loads as in Table 7. Table 7 Foundation load reduction factors No. of office floors Imposed load (kn/m 2 ) Reduction factor Equivalent load (kn/m 2 ) Austin [54] reported that two comprehensive studies, carried out in 1970 by CIRIA and 1992 by Stanhope, proved that 99% of office layouts, including allowance for the provision of IT equipment, can be accommodated in a 2.5 kn/m 2 capacity office without the necessity for further structural checks, provided the condition of the structure is satisfactory. Moreover, a load of 1.0 kn/m 2 for partitions relates to a floor slab to floor slab partition of plastered lightweight blockwork. Values of 0.6 kn/m 2 and 0.5 kn/m 2 are now more appropriate as these relate to floor-to-floor and floor-to-ceiling demountable partitions respectively. However, it may be that the client requires the imposed design loading to be 4.0 kn/m 2 as mentioned previously. In addition, some areas, if not the whole building, may require a structural appraisal if, for instance, heavy plant is being relocated or added, and subsequent strengthening may be required. An accurate structural appraisal will require a knowledge of the actual concrete strength and the actual amount, type and location of the reinforcement. The amount and location may be determined by an accurate cover-meter survey or by locally exposing the steel. The type of steel, that is its strength and bond characteristics, can only be 32 Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

45 CONDITION SURVEYS SECTION 3 obtained with any certainty by exposing samples in the structure and removing them for laboratory analysis. However, contemporary codes will give an indication of the grades of reinforcement available at the time of construction. If measurements of dimensions and strength have been taken, some of the uncertainty present at the design stage will have been removed, and the I Struct E [41] appraisal document therefore suggests lower materials partial safety factors than would be necessary for design purposes. Strengthening techniques are described in Chapter Structural stability The building structure, particularly if it is precast concrete construction, should be checked for robustness. Precast concrete buildings constructed prior to the collapse of the Ronan Point residential block in 1968, and up to 1972, are unlikely to comply with the stability and tie provisions required in current codes (such as BS 8110 [53] ), and ties will have to be added to bring the refurbished building up to present day standards Load tests In extreme cases it may be appropriate to carry out a load test on part of a structure, following the guidance given in Part 2 of BS 8110 [53]. This should only be done as a last resort, when analysis has failed to give a satisfactory answer. BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 33

46 SECTION 4 INTERACTION BETWEEN STRUCTURAL AND SERVICES WORK 4 INTERACTION BETWEEN STRUCTURAL AND SERVICES WORK There is no definite relationship between the amount or type of structural work that will be required in a refurbishment scheme and the refurbishment of the services. In some cases either one or the other will be carried out, such as structural work simply carried out on the external cladding of the building or the provision of new main plant using existing distribution systems etc. However, in many cases, significant refurbishment of services will require some structural work. This may range from simple tasks like drilling through walls to install ventilation ducts, to major structural alterations such as cutting out floor segments to install new lifts. Factors that may need to be considered are listed below. Possible solutions to the associated structural problems are covered in Section LOADINGS Plant is much lighter than twenty years ago. Boilers, chillers, fans, pumps and other equipment offers much higher output per unit mass than older plant. Loads on buildings have also been reduced due to less water storage, which is minimised by legislation and the desire to minimise capital costs. Also, water use has reduced due to fewer canteens and greater use of water conservation measures. Water tanks are now generally contained within buildings basements due to improved methods of system pressurisation. Water tanks are sometimes relocated from the roof to the basement as part of refurbishment to allow roof-top air conditioning chillers to be installed. Building services issues affecting loads on structures can include: requirement for increased floor loading, resulting in additional load on supporting beams, columns and the foundations (eg. due to addition of air conditioning plant) need to support heavier cladding system (eg. replacing single glazing with triple glazing) relocation of plant. These are described in greater detail in Section GEOMETRY OF THE STRUCTURE The geometry of the structure will have a significant impact on the routing of the services and the method of service provision. Particular aspects to be considered include: limited storey height desire for increased floor span between columns desire for increased floor area need to create openings in floors for lift shafts, vents, escalators, etc need to create atria to improve appearance and improve ventilation and natural light need to create holes/openings in beams for services 34 Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

47 INTERACTION BETWEEN STRUCTURAL AND SERVICES WORK SECTION 4 need to create openings in load-bearing walls (eg. shear walls) for access doors, etc need to provide additional lateral stability, eg. because of increased wind loading. These are described in greater detail in Section 6.3. Table 8 shows structural element types and the allowable modifications that typically can be made. This has implications for the type of services that can be provided and where they can be routed. If it is not possible to make a hole in a beam, for example, then either an alternative route will have to be chosen or an alternative method of service provision selected. 4.3 SELECTION OF SERVICES It is not possible to firmly link choice of building service system and type of structural element. There are too many factors affecting the selection of services, such as floor to ceiling height, the required specification for service provision (eg whether mechanical cooling can be justified), the size of floor layout and restrictions to routing of services such as position of risers, ease of adding external risers, ease of adding a raised floor, etc. Table 9 indicates some of the major issues when selecting air conditioning plant as part of a refurbishment. The problem of routing of services is discussed in Section 4.4. A further consideration is the use of the structure to incorporate services. Examples include: the use of exposed concrete ceilings as a source of radiant cooling [55] underfloor heating and cooling (embedded pipework) [56] embedded trunking for power and data cables (generally in the floor screed [57] but potentially precast trunkings in future) the use of hollow cores for provision of ventilation and as a means of conditioning the supply air [58]. Incorporating services within the structure can offer improvements in construction productivity, provide a robust solution to services provision and offer flexibility (with appropriate planning) and lower costs. BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 35

48 SECTION 4 INTERACTION BETWEEN STRUCTURAL AND SERVICES WORK Table 8 Allowable modifications to structural elements Structural element type When found Allowable modifications Solid one-way slabs with downstand beams Solid two-way slabs with downstand beams Flat slabs with or without drops Flat slabs with column heads (mushrooms) Ribbed, troughed and waffle slabs 1960s Cutting through the slab itself is not a problem avoid cutting reinforcement or trim. Services need to be parallel to the beams. If service runs not parallel to beams: Cut through beam limited to approx. 100 mm diameter holes; avoid reinforcement; do not cut in compression zone (top of beam or possibly bottom near columns). Run services beneath beams resulting in loss of floor to ceiling height. See section Generally as one-way slabs (above). Larger holes can theoretically be cut through the two-way Common now and in the 1980s, less common previously slab than the one-way slab. The critical zone is near the columns. Holes up to 100 mm can be accommodated. Holes greater than 100 mm would seriously reduce the resistance to punching shear from the column and would need to be trimmed with steel. Pre-1960s Cutting through mushroom heads is likely to prove impractical. Late 1960s, still popular Services must run under the ribs and any downstand beams. Ribs must not be cut through for horizontal service runs. Slab areas between ribs can be cut through for service risers with no detrimental effects. If ribs need to be removed for risers, trimming or brackets are required. Precast planks Small holes (up to 75 mm) may be cut through check with manufacturer so that reinforcing tendons are not severed. Larger holes require trimming. A plank may be able to be removed and a cradle added to accommodate service runs, provided adjacent members can take the additional load. 36 Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

49 INTERACTION BETWEEN STRUCTURAL AND SERVICES WORK SECTION 4 Table 9 Attributes of air conditioning systems for refurbishment (adapted from Good Practice Guide 71) [59] Centralised air systems Ventilation and heating - no air conditioning Suitability with low floor to ceiling height Operating cost Life cycle cost Ease of retrofitting Level of control Filtration Noise level Poor High Average Poor Good Good Low Constant volume (single zone) Poor High Average Poor Very good Good Low Variable air volume (VAV) Poor High Average to high Poor Good but complex Good Low Dual duct Poor High Average Poor Good Good Low Displacement ventilation Poor Average Average Poor Good Good Low Partially centralised air/water systems Centralised air with reheat Poor High Average Poor Good Good Low Induction units Average High High Poor Poor Poor Can be high Fan coil units Good or average High High Good or poor Good Poor Can be high Unitary heat pump Average High High Good Good Poor Can be high Chilled ceiling Good Average Average Good Good Poor Low Local systems Single sided ventilation Good Low Low Good Local only Poor Can be good Cross ventilation Average Low Low Average Poor Can be good Stack ventilation Average Low Low Poor Local only Poor Can be good Natural ventilation, exposed concrete ceiling slab, night cooling Average Low Low Can be good Local only Poor Can be good Heat and local ventilation - no air conditioning Good Low Low Good Can be good Can be good Can be high Through wall packages Good High Average Good Local only Split unit packages Good High High Good Local only Individual reversible heat pumps Good High High Good Local only Poor Poor Poor High High High Variable refrigerant flow Good High High Good Good Poor Can be high BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 37

50 SECTION 4 INTERACTION BETWEEN STRUCTURAL AND SERVICES WORK Table 9 Continued Centralised air systems Space required Plant room Office Duct Humidity control Maintenance Local Skill or level central Air distribu tion Ventilation and heating - no air conditioning High Low High None Central Medium Very good Constant volume (single zone) High None High Very good Central High Very good Variable air volume (VAV) High None High Good Both High Very good Dual duct High None Very high Good Both High Good Displacement ventilation High None High Good Central High Very good Partially centralised air/water systems Centralised air with reheat High None High Good Both High Good Induction units Low None or moderate Fan coil units Low None or moderate Moderate limited Both High Poor Moderate Limited Both High Fair to good Unitary heat pump Low Moderate Low None Both High Poor Chilled ceiling Low Low Low None Both High N/A Local systems Single sided ventilation None None None None Local Low Can be good Cross ventilation None None None None Local Low Can be good Stack ventilation None None None None Local Low Can be good Natural ventilation, exposed concrete ceiling slab, night cooling Heat and local ventilation - no air conditioning None None None or low None Low None or low None Local Low Can be good None Local Low Can be good Through - wall packages None Moderate None None Local High Poor Split unit packages Low None to moderate None None Local High Poor Individual reversible heat pumps Low Moderate None None Both High Poor Variable refrigerant flow Low None or moderate None None Both High Fair 38 Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

51 INTERACTION BETWEEN STRUCTURAL AND SERVICES WORK SECTION ROUTING OF SERVICES General The distribution of services in a building is classified into horizontal and vertical distribution. At the time of construction a common pattern of services distribution is required which benefits the construction process and makes subsequent services maintenance easier. The choice of services distribution method is made depending upon [60] : the nature of the building structure the layout required access to services the need for fire compartmentation available space in the building. In terms of refurbishment the means of services distribution is thus, to a certain extent, already determined. However, depending on the nature of the refurbishment, it may be necessary to alter the services distribution routes, perhaps in order to introduce mechanical ventilation or to increase the number of power or data socket outlets on each floor. The routing of services may be further complicated by the occupation of the building during the course of refurbishment. In this case the design should focus on keeping movement of staff to a minimum. The distribution of services in a building includes the routing of ducts, pipes and cables for: ventilation heating cooling lighting small power telecoms/data fire/smoke detection sprinklers. Not all of these services are required in the same place yet it is often expected that a single distribution zone (ceiling void, underfloor or perimeter trunking) serves the different locations of all these services. For example, heating is primarily required at the perimeter to overcome heat loss. Small power and data cabling is required at each desk, some of which may be positioned in the middle of the floor. Artificial lighting is generally positioned at ceiling level together with fire detection equipment and sprinklers, where required. The method of horizontal service provision will depend on the size and layout of the building, whether open plan or cellularised, and the type of services required. For example, the requirements of a cellularised naturally ventilated building will be quite different to large open plan office with full air conditioning. The majority of buildings are small, cellularised and naturally ventilated. These generally utilise perimeter services distribution which typically consists of heating, small power, and data/telecoms. Lighting is surface mounted on ceilings, which are BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 39

52 SECTION 4 INTERACTION BETWEEN STRUCTURAL AND SERVICES WORK typically of plasterboard construction. Where additional desks are added in the middle of a floor, power and data might be supplied via cables laid on the floor and protected by a rubberised cable protector. In more highly serviced buildings distribution of services typically follows the structural grid layout. This allows a modular layout of services which may include provision of heat, light, ventilation and air conditioning, electric and data services, sprinklers and fire/smoke detection. Whilst this arrangement provides the services even if they are not required, it does add flexibility to meet future requirements at a low cost. Perhaps more importantly, it avoids the problems that can arise when service outlets are provided at random which can lead to a disorganised and eventually unworkable jumble of cables, ducts and pipes in the service void. More recently, the use of service rafts has been increasing. These group together services such as lighting, fire alarm and acoustic treatment in a neat, purpose made unit that is then attached to the ceiling. This method seems likely to gain more ground as more new buildings require ceilings slabs to be left exposed whilst still requiring lighting, fire detection and acoustic treatment at high level. Such rafts have been used for lighting and acoustic treatment at PowerGen [61] and more recently as a services bulkhead at the Kimberlin Library extension at De Montfort University [62] and as a multi-service (or integrated) chilled beam incorporating chilled beam, lighting, PA, sprinklers, detectors and fire sounders [63] for the Lloyd's Register of Shipping Building Vertical distribution The structural detail of the building determines the vertical distribution of services. The number and position of risers provided is important to optimise the length and hence size of horizontal services, particularly ductwork. Duct sizes are largest where they leave the riser and decrease in size as branches are taken off. Making ducts too small will lead to high air velocities and hence noise. Typically, a riser should serve a floor area of between 15 and 23 m radius ( m 2 ) [64] and will account for approximately 2% of gross floor area. The floor area served will be reduced where the riser is to one side. Figure 2 and Figure 3 show typical position of risers within a building [65]. The addition of new risers as part of refurbishment is described in Section Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

53 INTERACTION BETWEEN STRUCTURAL AND SERVICES WORK SECTION 4 Figure 2 One main riser through the building [65] Note - Horizontal ducts below beams give deeper engineering zone than figure below. Figure 3 Distributed risers [65] Note - Horizontal ducts can be between downstand beams to give shallower engineering zone Horizontal distribution Horizontal distribution is also dependent on building structure. Buildings with loadbearing walls generally have flat slabs which, when combined with a suspended ceiling, allows services distribution in the void created between the two. The problem occurs when the loadbearing wall is to be penetrated and the frequency of penetrations leads to structural weakness. In this situation alternative services distribution routes should be sought or the number of holes made should be minimised. Where structural frames are used the approach depends on the thickness of the downstand beam. Wider spans have deeper downstand beams. If, for example, an air conditioning duct was to be routed below this beam then the ceiling services void becomes very large, up to approximately 1.5 m. This is acceptable if adequate floor to ceiling height has been provided, but in a refurbishment situation this may not be the case. Thus, alternative arrangements are normally made since large scale penetration of the beam is likely to be structurally untenable. A further problem occurs where supply and extract ducts cross over, requiring even greater depth. Other buildings may not have a ceiling BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 41

54 SECTION 4 INTERACTION BETWEEN STRUCTURAL AND SERVICES WORK void for services, and only a limited floor to floor height. Where it is required to add additional services, such as mechanical ventilation, other distribution arrangements have to be considered. Service distribution methods are described below Distribution solutions Common methods of distributing services in refurbished buildings include: Routing of services in the ceiling in sections so that the downstand beams are not crossed. The horizontal services may be fed from a central corridor (see Figure 4) or by the provision of additional vertical risers to feed each horizontal leg, similar to that shown in Figure 3. Note that lower ceilings can be accommodated in corridors and it may be possible to site fan coil units and other systems in this void and blow air into the occupied area. Figure 4 Services fed from a central corridor Adding vertical risers to the outside of the building. This may be difficult to achieve, depending on the scale of the refurbishment and the likely planning implications. It can also provide accessibility problems. However, it provides clear distribution runs and maximises lettable space (see Figure 5). Figure 5 External distribution of ducts [65] 42 Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

55 INTERACTION BETWEEN STRUCTURAL AND SERVICES WORK SECTION 4 Use of a greater number of smaller services runs. For example, it may be possible to split air flow into a number of smaller ducts. Further, the reduced duct size may allow penetration of the downstand beam at suitable intervals. The typical allowable hole size is up to one third beam depth and a maximum of one hole in a length equivalent to three hole diameters. Restricted space in many refurbishments encourages the use of many small ducts serving small zones rather than large ducts serving large zones. This ties in well with the current practice of separating ventilation and cooling (air based cooling systems are less efficient in providing cooling than water based systems due to the cost of transporting the cooling media). This reinforces the current emphasis on fan coil units and split units for cooling, together with the provision of local occupant controls. Re-routing services in an under-floor void. Raised floors provide an ideal method of air distribution to deep-plan areas. Floor grilles are positioned to provide the required air volumes to each zone and these are easily moved if loads change. However, in some buildings cable management has become a problem with perhaps three generations of cabling retained in the floor void, the removal of which may be required to give the required air flow path. Careful management of cable removal, leaving the working system intact, will be required. Underfloor distribution may become less important as structured cabling, fibre optic networks and cordless technology become standard installations. Where floor to ceiling height is restricted removal of the floor screed may be viable. This typically increases slab-to-slab height by 100 mm, reducing floor loads and creating sufficient space for a shallow raised floor allowing distribution of services within the void created. However, screed removal is expensive and time consuming. Where air supplies are required to local terminal units, such as wall mounted fan coil units or local air diffusers, small ducts may be run inside existing columns or may be added to each side and boxed in. The existence of mushroom head column caps presents a problem, although, in extreme cases these can be drilled to allow ductwork to pass through. The ductwork may be left exposed, particularly in educational buildings and canteens. Buildings on the Continent frequently leave services exposed. BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 43

56 SECTION 4 INTERACTION BETWEEN STRUCTURAL AND SERVICES WORK Case study: 338 Euston Road The floors of this 16-storey office building were extended by 1.5 m in each direction, adding 22% to the useable floor area on each level. The projecting floor trays were constructed of metal decking and 100 mm concrete topping reinforced by shear studs. The decking was fixed to a frame of four steel I-sections which was attached to the existing floor. The VAV ducts and boxes were fitted within the new frame. These were supplied from new vertical risers fitted between each projecting floor bay [66]. Case study: Park House, Teddington A 150 mm raised floor was made from high density particle board (30 mm thick) on concrete blocks to allow distribution of electrical and communications cabling. The change of level was dealt with by shallow ramps leading up from each entrance to the floor. The floor cost 22/m 2 of gross floor area [8]. Case study: Boots D10 building This 1930s concrete factory was partially converted to office accommodation, the rest remaining as manufacturing areas. The buildings' services remain exposed beneath the slab, although the pipework is clad to make it more aesthetically appealing. The exception is the sprinkler pipework which has been painted red and follows the contour lines of the concrete slab, actually accentuating the line of the internal structure- see Page Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

57 INTERACTION BETWEEN STRUCTURAL AND SERVICES WORK SECTION 4 A summary of the advantages and disadvantages of each distribution method is given below: Ceiling Advantages can accommodate all services where space allows can make use of space between beams ideal for air distribution in large open plan areas if beams allow careful services routing may obviate the need for a suspended ceiling, allowing increase in floor to ceiling height ceiling extract system via light fittings allows removal of emitted heat. Disadvantages co-ordination of services can be a problem access requires a ladder potential maintenance damage to ceiling tiles possible problems fixing to ceiling as part of a refurbishment, eg for trunking, ductwork and pipework supports etc. services can be unsightly where it is required to leave ceiling exposed. Floor Advantages can accommodate all services where space allows ideal for air distribution in large open plan areas can be used for extract system as well as supply need for ductwork is minimised relocation of floor grilles to suit new layouts is simple low pressure loss air distribution system ease of providing power, communications and data cables to all areas, particularly in large open plan areas may eliminate the need for a suspended ceiling. Disadvantages air flow can become restricted by high density of cables adds weight and height - may lower height of ribbon windows and affect sight lines possible problem linking lifts and stairwells. Perimeter Advantages skirting and dado rail trunking is relatively cheap fan coils can use air direct from outside and can be used to overcome perimeter heat loss/gain problems electrical, data and pipework services may be buried in the floor screed. Floor boxes for small power and data connections may be left flush in the screed or incorporated as part of a raised floor. This particularly suits narrow floor plates with limited floor to ceiling height. Disadvantages air supply limited to perimeter zones may require ductwork, cable, pipework drops from above or below reduces lettable area difficult to service large open plan areas. BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 45

58 SECTION 4 INTERACTION BETWEEN STRUCTURAL AND SERVICES WORK Fixings from floor slabs (Reproduced from: Architects' Journal, 19 March 1986.) When refurbishing buildings it is important to establish at an early stage how services can be suspended from existing floor slabs. Constructions such as hollow pot floors, precast units, trough and waffle slabs and filler joists restrict the positions and types of fixings independently of the overall load capacity. Difficulties and delays can occur on site when the fixing problems have not been resolved in the design of the new services installation. Suggested methods of fixing are given below. In situ flat slabs Fixings to the soffits are straightforward. With precast or prestressed floor units, fixing should be arranged so as not to damage or impair the reinforcement or prestressing tendons. Voided construction In voided construction, fixings are not straightforward. They include: toggle fixing (item 1 in Figure 6) through the pot for light loads such as light fittings and cable conduits, but not suspended ceilings plug and screw or expanding anchor bolt (item 2 in Figure 6) into the centre of the rib - check there is enough space between the reinforcing bars for heavy loads, drop rods (item 3 in Figure 6) can be fitted through the slab, with a fixing plate on top - this is only suitable where screeds cover fixings. Figure 6 Possible fixings to soffits in voided construction 46 Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

59 INTERACTION BETWEEN STRUCTURAL AND SERVICES WORK SECTION 4 Exposed rib construction In exposed rib construction, fixing is more affected by the location of reinforcement. Suitable fixings include: plug and screw fixing for light loads (item 1 in Figure 7) expanding anchor bolts to the sides of ribs, positioned to miss any reinforcement (item 2 in Figure 7) drop rods from fixing plates on top of the slab, and covered by the screed (item 3 in Figure 7). Figure 7 Possible fixings to soffits of exposed ribs BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 47

60 SECTION 5 BUILDING SERVICES REFURBISHMENT OPTIONS 5 BUILDING SERVICES REFURBISHMENT OPTIONS 5.1 OVERVIEW The extent of refurbishment of the services within a building will depend upon many factors including the building age, use, expected rental value, the type and condition of existing services etc. This section provides an overview of the services options available and their relative benefits and disadvantages when applied in a refurbishment situation. The final selection of the most appropriate services will be decided by the designer based on consideration of many factors. Reasons for refurbishment (Section 1.2), assessing the condition of existing building services (Section 3.1) and interaction between structural and services work (Section 4). The principal attributes of different services options are outlined below. 5.2 FACADE General requirements The facade serves many purposes. It provides the external aesthetic value of the building, the point of entry into the building and may add structural strength and rigidity. It may allow ventilation and natural light to enter, yet prevents ingress of the elements. It can incorporate solar shading, noise attenuation, insulation against heat loss and heat gain, and more recently, collection of solar power for hot water and electricity generation. There are many parameters to satisfy and consequently, many variations available. The following describes the building services related aspects of the facade. Structural aspects of cladding are discussed in Section 6.6. Table 10 Standard U-values [32] Insulation requirements and methods of provision Wall U-values should be 0.45 W/m 2 K to meet current Building Regulations. However, there is currently no requirement under the Building Regulations to add or replace wall insulation during a refurbishment, although it is good practice to upgrade insulation to meet, or exceed the current requirements of Part L of the Building Regulations [32]. Using the elemental method given in Part L: Building Regulations 1995 [32], standard U-values are as follows: Element U-Value (W/m 2 K) Roofs 0.25 Exposed walls 0.45 Exposed floors and ground floors 0.45 Semi-exposed walls and floors 0.6 Windows, personnel doors and rooflights 3.3 Vehicle access and similar large doors Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

61 BUILDING SERVICES REFURBISHMENT OPTIONS SECTION 5 This applies where windows and doors account for up to 40% of the exposed wall area in offices and roof lights represent up to 20% of the roof area. Alternatively, the energy use method can be used which gives greater freedom of building design, so long as the total annual energy use of the building is less than the calculated annual energy use of a similar building designed to comply with the elemental method, and that the U-values of exposed walls, roofs and floors are not above than 0.7 W/m 2 K. Insulation levels for new buildings have to meet Building Regulation requirements and this leaves a grey area where demolition is carried out to the point that the refurbishment essentially becomes new build. However, as already mentioned, good construction practice will include replacement of insulation as part of refurbishment to meet current Building Regulations Windows Where windows are being replaced good practice suggests that the average U-value of the windows does not exceed 3.3 W/m 2 K, in accordance with the current requirements of Part L of the Building Regulations [32], although this is not currently a Building Regulation (except where glazing is to be replaced under Part N: Glazing: safety in relation to impact, opening and cleaning). Part L of the Building Regulations [32] requires that double glazing, or better, must be used. Where glazing is fitted at low levels it may be possible to replace this with insulated infill panels. Where existing windows are being retained it is recommended to upgrade single glazing to bring the construction into line with current Building Regulations. The choice of window is also important for a number of other reasons including: ventilation capacity ease of opening and provision of fine adjustment of opening position security seal effectiveness interference with blinds. Further information on the selection of windows is given in: Window design [67] Natural ventilation in non-domestic buildings [68] Selectingenergy efficient windows [69] Refurbishment of air-conditioned buildings for natural ventilation [8] Air infiltration through the facade - air leakage testing Uncontrolled (adventitious) ventilation should be reduced or prevented through use of good draught stripping around windows, doors and rooflights. Gaps between ceilings, floors and walls should also be sealed as should vapour control membranes. Where services enter buildings or conditioned spaces these should have proper seals. Lift shafts and service cores should also be sealed from the conditioned zone. Further guidance is provided in Minimising air infiltration in buildings [70]. Where sealing is undertaken the provision of controllable BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 49

62 SECTION 5 BUILDING SERVICES REFURBISHMENT OPTIONS background ventilation, normally in the form of trickle ventilation, should be considered. Completed buildings should be pressure tested in accordance with the methodology given in Air tightness specifications [71] Shading systems - internal, external, mid-pane, solar control glass Solar control is particularly important in order to reduce summertime internal temperatures in naturally ventilated buildings and to reduce air conditioning loads and associated costs in air-conditioned buildings. Ideally, winter time solar gains will be allowed to provide a space heating effect. The four principal solar control methods can potentially all be added as part of a refurbishment. The methods are: internal shading devices (normally blinds) mid-pane shading devices (blinds) external shading devices (including shutters, fixed louvres, blinds, fixed projections, canopies, trees) solar control glass. The type of solar control will depend upon the nature of the refurbishment, the orientation of the facade, the glazed area, the budget and any other restrictions, such as planning constraints applying to the building. The shading method selected may have a significant impact on establishing whether to replace the window and/or glazing. As a rough guide, glazed areas up to 50% of wall area can use internal shading whilst above this value external shading or solar control glass will be required to keep internal conditions comfortable in summer [8]. However, where solar control glass is used solar control is achieved at the expense of natural light transmission, increasing the use of artificial light and excluding potentially useful solar gains in winter Daylighting The use of daylight should be considered for all refurbishment projects. Not only does it provide potential energy savings but it improves occupant sense of well-being. However, to maximise use of daylight it is important to avoid glare as this will result in blinds being operated and artificial lights coming on. In order to improve the uniformity of light provided and hence minimise glare the use of light shelves, prismatic glazing, splayed reveals and light-coloured surfaces on walls and ceilings to increase the reflectance of surfaces, should be considered. The introduction of daylight can be difficult in a refurbishment. Daylight penetration is limited in a deep plan building: the average daylight factor (% of outside illuminance) falling rapidly with increasing distance from a window, from over 5% near the window [67] to less than 1% approximately 5 m from the perimeter. The main influence on daylight level is the percentage glazed area. For a good compromise between daylight and solar gain on facades receiving direct sunlight, a rule of thumb is to have a glazed area between 30-50% of the total wall area. Larger areas could replace some glazing with insulated 50 Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

63 BUILDING SERVICES REFURBISHMENT OPTIONS SECTION 5 opaque panels or solar control glass. North facing facades do not suffer from solar gain so maximum use should be made of these for natural lighting. Other solutions for deep plan natural lighting are the addition of a lightwell or atrium, which may be feasible in a complete refurbishment scheme. An alternative low cost solution for cosmetic refurbishments is the use of daylight tubes such as SunPipe [72] which are ideal for introducing light into deep plan areas, corridors and storage areas, even in situations where there are one or more floors above them. 5.3 CEILINGS AND FLOORS Ceiling slabs are either covered by a suspended ceiling or left exposed. Suspended ceilings provide a clean, modern finish to the office landscape as well as hiding the building services and structure. They provide the ability to attenuate noise, to act as an air extract plenum and to integrate services such as sprinkler heads, ventilation grilles, heat and smoke detectors and lighting. They may also incorporate cooling (chilled ceilings). However, the need to provide access to the services above the ceiling can lead to tile damage. In buildings predating the 1970s the ceilings were generally intended to be left exposed. Floor plates were shallower and services were distributed around the building perimeter, with the exception of lighting, which was ceiling mounted. These buildings were predominantly naturally ventilated. The 1990s have seen a greater interest in the benefits of leaving concrete ceilings exposed in order that the slab can absorb daytime heat gains, which are subsequently dissipated at night via passive ventilation through windows or purpose built vents. Whilst many buildings dating from the 1960s and 1970s cannot fully remove the suspended ceiling due to the poor nature of the surface beneath, it may be possible to achieve some of the benefits by the use of egg crate ceiling tiles which do not isolate the slab from the space below. Other buildings may leave their services exposed on the ceilings, having first encased them in high quality insulation or more aesthetically pleasing containment. This saves the cost of the ceiling and allows ready access to the services. The design of pipework, ductwork, cable trunking etc and associated insulation, cladding and support systems should facilitate cleaning. Sound transmission with flat ceilings may be a problem. Sound absorbing panels are available which can be used in a variety of ways [8,61] : as baffles hanging from the ceiling to form a partial suspended ceiling if floor to ceiling height allows as part of a suspended luminaire design as wall panels as free standing partitions. Other problems may arise with solid concrete floors due to footfall noise which can be overcome with floating or raised floors. Raised floors are now generally considered to be essential for commercial buildings. They provide flexibility of distribution of small power and communications to desks, particularly in deep-plan buildings and can also provide a distribution route for other services. More recently the floor void created has been used as the ventilation duct with BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 51

64 SECTION 5 BUILDING SERVICES REFURBISHMENT OPTIONS displacement type systems with the advantage that floor grilles can be readily moved to suit organisational requirements. In refurbishment situations raised floors can be added providing that there is adequate floor to ceiling height, ie at least 2.4 m excluding the raised floor and suspended ceiling. Where a suspended ceiling is already present it may be possible to remove this or to reduce its depth in order to facilitate the provision of the raised floor. However checks should be made to ensure that sill heights are not unduly compromised. Raised floors can be used to provide services to both that floor and the one below, eg for lighting, although this arrangement can cause problems if there is multiple tenancy of the building. Case study: Park House, Teddington The concrete ceiling of this early 1960s office block has been exposed, skimmed with plaster and finished with white emulsion paint for good reflectivity. No acoustic treatment was considered necessary, with floors and furnishings providing enough sound absorption to keep reverberation times acceptably short. The cost of making good the ceiling, skimming with plaster and subsequent painting equates to 12/m 2 of gross floor area [8]. 5.4 VENTILATION AND AIR- CONDITIONING General refurbishment ventilation strategy Adequate ventilation within a building is necessary to maintain the occupants health and comfort. This may be provided by natural or mechanical means. The current emphasis is only to use mechanical ventilation and air conditioning where it can be justified. Where projects are speculative then the facility to provide mechanical ventilation may be allowed for but not installed. This reduces the cost of refurbishment. The selection of the ventilation strategy is based on a combination of: the expected heat gains in the space. Typical office heat gains are: - IT loads 10 W/m 2 - Occupant density (1 person every 10 m 2 ) 9 W/m 2 - Lighting 10 W/m 2 Low glazing ratio and good shading minimises solar gain. the need to avoid nuisance draughts - air velocities should be less than 0.25 m/s in summer and less than 0.15 m/s in winter. For naturally ventilated buildings this restricts the depth of space that can be ventilated. The position of vents is also important. the need to provide sufficient air changes for occupant health and comfort. This is generally the winter design condition. 52 Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

65 BUILDING SERVICES REFURBISHMENT OPTIONS SECTION 5 Other factors affecting choice of ventilation strategy include the cost of changing ventilation strategy, the potential for re-use of existing components, expected improvement in internal environment and potential rental increase. Where heat gains are above 30 W/m 2 and the plan depth is greater than 7 m for single sided ventilation (12 m for cross-ventilation), then natural ventilation is unlikely to be suitable on its own and will require either a mixed mode solution or full use of mechanical systems. Mechanical ventilation will also be required where there is high occupant density and it is not possible to introduce adequate natural ventilation without causing draughts Natural ventilation strategy There are many recently published texts covering this subject [8,68,73]. The majority of buildings were designed to use natural ventilation, particularly those before the 1970s. In refurbishing a naturally ventilated building the following should be considered: Windows for single sided ventilation should be tall or preferably have a top and bottom opening to allow local stack effect to set up convection circulation. Cross-ventilation requires a very open plan, with minimal resistance to flow. Partitions should be low (<1.2 m). Tall filing cabinets and other furniture likely to impede air flow should be placed around perimeter walls, between windows. Cellular rooms should not be placed around the perimeter. They reduce air movement and restrict the view out. Windows with top vents are effective in promoting cross-ventilation at high level with no draughts at desk height. Central corridors with full height partitions should be removed to promote cross-ventilation. Where cross-ventilation is not feasible, or the plan is particularly deep, the use of stack ventilation may be possible. Existing vertical shafts through the building such as stairwells, risers, ducts and lift shafts can provide the stack, with appropriate fire control, perhaps with replacement risers, stairwells etc added to the outside of the building. Alternatively, air can be introduced and extracted using ventilation products such as Windcatcher [74]. This is a segmented ventilation shaft which passively introduces air to the space through some segments whilst extracting via others. This also offers the benefit of potentially cleaner air from the roof area rather than street level. Further details on introducing natural ventilation into buildings can be found in Refurbishment of air-conditioned buildings for natural ventilation [8]. The removal of perimeter cellular offices should be considered as part of the refurbishment in naturally ventilated buildings. This allows maximum use of natural ventilation, improves the quality of the BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 53

66 SECTION 5 BUILDING SERVICES REFURBISHMENT OPTIONS Table 11 Benefits/disadvantages of natural ventilation environment and provides external views. These are important considerations as it has been shown that where occupants are able to control their own environment they are more tolerant to changes in internal conditions [75]. The addition of measures such as solar shading, lighting control, night cooling and exposed ceiling slabs allows the application of natural ventilation in buildings that were likely to have previously been mechanically cooled. The addition of these measures both reduces heat gains and allows an additional 15 to 20 W/m 2 of heat gains to be removed, making natural ventilation appropriate in buildings with a total heat gain of up to 40 W/m 2. Refurbishment should consider the application of these strategies to create comfortable buildings at low capital and running cost. Potential benefits Low capital cost Low maintenance cost Occupants potentially more comfortable Occupants potentially more productive Ease of provision of local occupant control Potential disadvantages Greater chance of overheating (heat gain limits) Possible draughts (leading to closing of windows) Design not so easy with high level of external noise Design may not be tenable with high level of external pollution, although mechanical ventilation may not be any better - depends upon the nature of the pollutant Deep plan ventilation limits Night cooling not possible with 24-hour occupation Precise flow rate control is not achievable May be affected by weather (especially rain) Security issues with open windows Mixed mode systems A combination of natural and mechanical ventilation systems, possibly with mechanical cooling, is termed mixed mode. It offers the benefits of both ventilation methods, and is often associated with environmentally friendly design due to the incorporation of measures to minimise heat gains such as solar shading, lighting control, use of exposed ceilings, careful positioning of high heat release office equipment, etc. The use of natural ventilation satisfies some clients' requirements for openable windows, reduced running costs and a green image. The use of mechanical ventilation allows provision of adequate winter ventilation, which is often considered a problem in larger office buildings due to the difficulty of introducing draught-free natural ventilation into large open plan spaces. Further, the use of mechanical ventilation allows addition of mechanical cooling if necessary. This is seen as important to satisfy the demand of some clients for limited peak internal temperatures, and future-proofs the building from the developer's viewpoint so that, even if mechanical cooling is not required now, it can easily be added for future tenants. Mixed mode buildings have been categorised by operation and type as follows [75] : contingency: where provision is made for future addition of mechanical systems 54 Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

67 BUILDING SERVICES REFURBISHMENT OPTIONS SECTION 5 parallel: both natural and mechanical ventilation are in use at the same time changeover: possibly using mechanical ventilation during the summer and winter with natural ventilation being used in spring and autumn zoned: localised areas such as conference rooms and dining areas use mechanical ventilation. In terms of refurbishment, mixed mode is often used since it is seen as offering lower capital and operating costs than full air-conditioning, and provides an improved internal environment compared to using natural ventilation only. Case study: Howard House, Bristol The refurbishment of this 1960s office building provided a combination of natural ventilation via the existing openable windows together with a quasi-displacement ventilation system which made use of the existing induction system ductwork. The old perimeter induction units were removed increasing the net lettable floor area by approximately 7.5%. - see Page Mechanical ventilation and air conditioning Mechanical ventilation systems are either centrally or locally based. Centralised systems are based around an air handling unit and provide central conditioning of the air (filtration, heating and possibly cooling and dehumidification) which is then distributed via ductwork to the space. Extract fans are provided to remove air, possibly recirculating part of it to recover energy. Partially centralised air/water systems provide local reheat or cooling to provide fine control of space temperature. Local systems provide combinations of outside air, heating and cooling (packaged through-wall units, reversible heat pumps, split units, variable refrigerant volume). Types of air conditioning system are shown in Figure 8 [59]. There are many variations to these systems and often different systems are used in a building as part of a mixed mode solution, either intentionally or to meet changing heat loads and occupant requirements. System selection is primarily dependent on the heat gains expected, the budget available, the condition of the existing plant and the space available. Refurbishment often provides the opportunity to rationalise ventilation and air conditioning, offering scope to reduce running costs. The attributes of different systems are described in the text below. BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 55

68 SECTION 5 BUILDING SERVICES REFURBISHMENT OPTIONS Figure 8 Types of air conditioning system [59] Ventilation Only Air Conditioning Natural Ventilation Mechanical Ventilation Via Atria Ventilation Local Centralised Centralised Partially Centralised Local Systems Air Systems Air/Water Systems Constant Volume Variable Air (Single Zone) Volume (VAV) Dual Duct Centralised Air Induction Fan Unitary With Reheat Coil Heat Pump Through Split Unit Individual Variable Wall Packages Packages Reversible Refrigerant Heat Pumps Flow Rate Centralised systems General The provision of central systems offers several potential advantages over localised systems, as shown in Table 12. Table 12 Potential benefits/disadvantages of centralised systems Potential benefits Plant is generally located in plant rooms making maintenance less disruptive to building occupants Heat recovery is easier Likely to be more cost effective in large installations Control system requirements may be less intensive Air extract system allows creation of positive or negative pressure in the space Ease of provision of air filtration, humidification and de-humidification Ease of provision of free cooling Potential disadvantages Plant failure may mean rapid loss of comfortable internal environment Ductwork distribution may be difficult Distribution of air for heating and cooling purposes is not as efficient as water systems Local occupant control may not be possible Air balancing may be difficult None None 56 Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

69 BUILDING SERVICES REFURBISHMENT OPTIONS SECTION 5 Constant volume ventilation systems provide robust, low cost systems and deliver fixed volumes of heated, cooled, filtered, humidified and/or dehumidified air to the space. They are not suitable for providing temperature control in areas with different heat loads. Displacement ventilation introduces low velocity air at low level, through floor or low level wall mounted diffusers. This air is approximately 2 K below room temperature. As the air temperature increases due to internal heat gains, the air rises to ceiling level and is exhausted. This provides high air quality due to removal of entrained contaminants. The method is less suited to buildings with low ceilings. Induction units are combined air/water systems that are normally located on perimeter walls to overcome solar gain and winter heat loss. They are supplied with centrally conditioned air, which, by use of nozzles, entrains a proportion of room air. This air is then heated or cooled to meet the temperature setpoint. VAV (variable air volume) - generally assumed to be a less favoured option for refurbishment schemes due to the large ductwork required which generally has to be routed in the ceiling void, as well as the services void required for the VAV boxes which should be at least 500 mm. Further problems can arise with over-sizing of VAV boxes due to overestimated heat loads which can lead to draughts and problems with overcooling of the space - VAV systems rarely have sufficient turndown to meet reduced loads. Further, fan loads are high and there are often problems with zoning. South facing zones have different heat loads to northerly zones and this can make scheduling of supply air temperature difficult. Nonetheless, VAV is still popular for large city developments as an alternative to fan coil units, either system being considered as a prerequisite to obtaining high city centre rents. Chilled ceilings/beams provide sensible cooling via unobtrusive overhead ceiling panels or beams. Beams require an air flow over them and thus, if a ceiling tile is positioned beneath, it must have a large free area, typically greater than 50%. The ceilings typically operate with chilled or cooled water between 14 C and 18 C, thus offering the potential to utilise cooling water sources other than chillers, for example via ground water cooling, dry coolers, or other heat dumps such as lakes. However, it should be noted that cooling output is reduced when operating with higher temperature water associated with these alternative cooling sources. Chilled ceilings give quiet, draught- free operation. Typical maximum loads are 70 W/m 2 for ceiling panels and 150 W/m 2 for beams. The provision of ventilation is essentially a separate function and may be via ducted mixed air systems, displacement ventilation or natural ventilation. Chilled ceiling panels give primarily radiative cooling whereas beams provide a mixture of convective and radiative cooling. Since the mean radiant temperature is reduced, the dry bulb temperature can be allowed to rise above normally acceptable comfort limits. There are a number of advantages of using chilled ceiling panels in refurbishment applications: BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 57

70 SECTION 5 BUILDING SERVICES REFURBISHMENT OPTIONS The ceilings are ideal where there is a restricted floor to ceiling height. Some systems have been fitted utilising only 200 mm. They do not take up wall space, possibly improving space utilisation and maximising lettable area. Iit may be possible to add additional cooling panels, thus offering flexibility to cope with future additional heat gains. insulation Figure 9: Chilled ceiling panel 1200 copper pipe containing chilled water 600 perforated plate Case Study: DTI Building, London The DTI Building in London used chilled ceiling panels to provide the required amount of cooling in a ceiling void of 200 mm, thus leaving sufficient space for a raised floor to be installed as well Localised systems Table 13 Benefits/disadvantages of localised systems General Localised systems offer advantages over central systems as shown in Table 13. Potential benefits Occupant control is easily facilitated Fine control of temperature conditions Ease of adding extra capacity Flexibility Little plant room space required Water distribution systems less bulky than central air handling ductwork and easier to route in refurbishments Potential disadvantages Difficulty of providing air filtration, humidification and dehumidification Maintenance costs higher and potentially more disruptive to occupants May be difficult to provide free cooling May be difficult to apply in large open plan areas Net lettable area may be reduced Can be noisy Electrical wiring more intensive 58 Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

71 BUILDING SERVICES REFURBISHMENT OPTIONS SECTION 5 Fan coil units (FCUs) are generally assumed to provide the most flexible cooling medium but have high maintenance and running costs. They are robust and easy to control but require increased electrical distribution, and may be noisy in operation. FCUs typically require a depth of 450 mm and may be located in the ceiling void, around the perimeter or on internal walls, or may be free-standing. Perimeter location of units reduces lettable area. They may be supplied with ducted conditioned or un-conditioned outdoor or recirculated air, or a combination of both. Fan coil unit systems might be designed with a capacity of 500 kw but provided with a chiller of 300 kw on the basis that location of maximum heat load is not known but certainly will not be apparent throughout the building. NB Split systems are similar to fan coil units as far as the room-mounted part is concerned, but cooling is provided by refrigerant rather than chilled water. The refrigeration part is normally mounted away from the occupied area. VRV (variable refrigerant volume) - typically defined as an air conditioning system comprising an outdoor unit containing one or more variable speed compressors (inverter or stepped), heat exchangers, accumulator, receiver, expansion device and controls, linked via a single flow and return refrigerant pipework system to a number of indoor units containing a fan, heat exchanger, expansion device and controls. Each system contains at least two indoor units (up to a maximum of 30 units) and one outdoor unit [76]. VRV is ideal for providing spot cooling to areas subjected to high heat gains. The system may also be designed to provide heating, with the advantage that a VRV system supplying heat has minimal distribution losses compared to say a four pipe fan coil system. With the fan coil system the boiler system must be at operating temperature with pumps running and water circulating etc during the operating period for the fan coil to be able to respond. However, where spot cooling requirements continue to grow, it may be more cost effective in the long term to provide a central cooling system (ie. ducted central system or chilled ceiling). BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 59

72 SECTION 5 BUILDING SERVICES REFURBISHMENT OPTIONS Table 14 Relative air conditioning capital and running costs (1993) (based on gross floor area) [59] Centralised air systems Capital /m 2 Costs Energy /m 2 /year Maintenance CO 2 emission kg/m 2 /year Ventilation and heating - no air conditioning Constant volume (single zone) Variable air volume (VAV) Dual duct X 3.4 Medium Medium Medium to high Medium X 55 Partially centralised air/water systems Centralised air with reheat Medium to high Induction units High 50 Fan coil units High 55 Unitary heat pump Local systems Medium to high Heat and local ventilation - no air conditioning Low 17 Through wall packages 70* 3.5 Low 75 Split unit packages Individual reversible heat pumps Variable refrigerant flow 85* Medium to high Medium to high Medium to high * = excludes separate provision of heating, x= system fitted with variable speed fan Figures are indicative only, and detailed calculations are necessary before comparisons are made. The numbers and ranking may be affected by building use and the design of the chosen system. Capital costs exclude related building work and cost of building management systems. Ventilation and heating systems are shown in comparison with air conditioning systems. Areas referred to are the total building area measured inside the external wall, ie gross floor area. 5.5 HEATING AND HOT WATER Buildings constructed in the 1960s were typically naturally ventilated and used low pressure hot water radiators. Modern boilers are far smaller and much more efficient than their predecessors, offering the potential of reducing plant room size. Boiler controls are a requirement of Part L of the Building Regulations, see Section When sizing replacement heating systems the effects of improving the fabric insulation and reducing air infiltration should be taken into account. New boilers between 4 and 400 kw have to meet the efficiency required by the Boiler (Efficiency) Regulations, see Appendix A Boilers operate for most of the time at part load so provision of multiple small boilers instead of one large one meets the demand profile more 60 Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

73 BUILDING SERVICES REFURBISHMENT OPTIONS SECTION 5 readily and efficiently. Condensing boilers improve on high efficiency boiler performance by passing return water through a heat exchanger to recover heat from the flue gas. Thus, the lower the return water temperature the more heat is recovered from the flue gas. Where central boiler plant serves more than one building decentralisation should be considered. Similarly, where a single boiler supplies both heating and domestic hot water, provision of a separate domestic hot water boiler should be considered so that the main space heating boiler can be turned off during the summer. Point-of-use water heaters may provide a viable option, reducing the need for long distribution pipework and associated heat losses. If existing distribution pipework is to be re-used as part of the refurbishment then lagging should be checked, particularly where it runs through unheated areas. Where pipework becomes redundant then it should be isolated or removed. Control zones should also be checked so that zones are created to meet the different heat demands for different parts of the building. 5.6 ELECTRICAL SERVICES Lighting installation Refurbishment of artificial lighting offers the opportunity to replace inefficient fittings or to fit high efficiency reflectors to improve illuminance. This may result in a reduction in the number of lamps to produce the same illuminance. The choice of luminaires will depend on the areas to be lit. For example, interior areas, car parks and display lighting all have different requirements. The energy efficiency of lamps and starters should be considered as well as access to change lamps. Further details on the selection of luminaires and lamps can be found in the CIBSE Code for interior lighting [29], Energy efficient lighting in buildings [77] and Energy management and good lighting practices [31]. The application of automatic lighting controls should also be considered, particularly for open plan offices. Schemes that use manual on and automatic off are most common. Toilet lighting controls should also be fitted. These are normally occupancy detectors with a timed off Electrical installation Any new electrical installation is intended to suit the occupiers' needs for twenty years or more. It is therefore essential that any future load growth and the need for flexibility are considered during design. Businesses now tend to re-organise more frequently, and the use of IT is likely to continue to increase. Sufficient distribution circuits and fixed socket outlets should be provided for business purposes. These are often in the form of underfloor bus bar distribution systems or dado rail power circuits. Similarly, adequate power supplies for future plant requirements should be allowed for, particularly where space is included for future addition of mechanical cooling. BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 61

74 SECTION 6 SOLUTIONS TO STRUCTURAL PROBLEMS/OBSTACLES 6 SOLUTIONS TO STRUCTURAL PROBLEMS/OBSTACLES 6.1 CONCRETE REPAIR Following the structural inspection and appraisal of the building, described in Section 3.2, repair to parts of the concrete may be required. A European standard ENV [78] for the protection and repair of concrete is currently being developed and the parts that are available are being used on a voluntary basis. The standard will become mandatory within the next few years. It covers the following: surface protection systems (coatings) structural and non-structural repair (mortar and concrete) structural bonding concrete injection grouting (to anchor reinforcement or fill voids) reinforcement corrosion protection. Until ENV 1504 is complete, guidance will have to be sought from other sources such as those decribed in the following sections Non-structural concrete repairs Non-structural repairs will not increase the load-carrying capacity of the structure. Details are as follows: Spalled or defective concrete should be tested with a hammer to determine the extent. Any defective and deteriorated concrete should be cut away and the reinforcement cleaned where corroded. A bonding coat should be applied and the repair material, which may be a mortar mix or a concrete mix depending on the size of the area, may be applied by trowel or sprayed on. There are many proprietary systems on the market for carrying out this type of repair. Defective floor slab joints should be routed out and re-sealed. Spalled arrisses should be cut out and made good with an epoxy mortar and the joint re-sealed. Non-structural cracks (ie no movement): Small cracks should be repaired by wire-brushing the surface and applying a thin grout, mortar or epoxy. Larger cracks should be cut out down to the reinforcement and filled with a modified cement/sand mortar. Alternatively crack injection can be used to repair deep cracks or cracks that pass all the way through the member. A polymer such as an epoxy resin should be applied to rebond the concrete thus improving structural strength and waterproofing the area. The work should be carried out by an experienced specialist contractor. Movement cracks should not be repaired with rigid materials but with a mastic, thermoplastic or elastomeric compound. Many proprietary systems are available. 62 Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

75 SOLUTIONS TO STRUCTURAL PROBLEMS/OBSTACLES SECTION 6 Honeycombed concrete should be removed and a patch repair carried out with cement mortar or a 10 mm aggregate concrete, depending on the size and depth of the area. The Concrete Society Technical Report No. 22 [79] gives detailed guidance on the identification and treatment of non-structural cracks in concrete Structural concrete repairs Structural repairs will be necessary in areas of serious damage. Methods for strengthening are covered later in this chapter. The various repair options are as follows: Plate bonding with steel or fibre reinforced plastics can be carried out to strengthen members and connections. Refer to later parts of this section. Cathodic protection, although rarely necessary on buildings, can be applied to reinforcement which has corroded due to chloride ingress [80,81]. Care must be taken to avoid future ASR attack which may result from such treatments. Chloride extraction is an alternative to cathodic protection and can be used to drastically reduce, but not eliminate completely, chloride levels. Again care must be taken to avoid future ASR attack which may result from such treatments. Realkalisation, although rarely necessary on buildings, can be used where the reinforcement has corroded due to carbonation. The process restores the alkalinity around the steel to halt the corrosive reaction. The process supplements patch repairs. Care must be taken to avoid future ASR attack which may result from such treatments Coatings/barrier systems Coatings and barrier systems can be applied on their own or to repaired areas to inhibit the aggressive actions which damage the concrete. The use of coatings and barrier systems is more common than concrete repair. The following systems are often used and many are proprietary: bituminous - hot or cold applied chlorinated rubber polymers acrylic epoxies polyurethanes silicones and silanes waterproofing decorative carbon dioxide-resisting resistant to chloride ingress resistant to water/moisture ingress protecting from chemical attack efflorescence-inhibiting. BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 63

76 SECTION 6 SOLUTIONS TO STRUCTURAL PROBLEMS/OBSTACLES The Concrete Society Technical Report No. 50 [44] gives details of the applications of these types of treatment Repairs to fire damaged concrete Repairs to fire damaged concrete need special consideration and this is not covered in this publication. Further information on the assessment and repair of fire damaged structures can be found in publications dedicated to the subject such as Repair, protection and waterproofing of concrete structures [82] and Concrete Society Technical Report No. 33 [83]. All repairs should be regularly monitored and maintenance will be required to coating systems. 6.2 INCREASED LOADINGS General If the floor loads are to be increased significantly, the strength of the slab and the supporting members must be checked. It will also be necessary to determine whether the resulting deflections will be within acceptable limits. Any assessment of the structure should be on the basis of the actual geometry and material properties and should be in accordance with the Institution of Structural Engineers report Appraisal of existing structures [41]. If the calculations suggest that the members are under-strength, it will be necessary to adopt approaches such as strengthening the members or increasing the moment capacity at supports. Various possible approaches are given in the following sections and summarised in a matrix in Section Each broad approach is considered briefly. It should be emphasised that there is no single best option: every application must be considered individually to determine the most appropriate and cost effective solution. As well as strengthening, it may be appropriate to consider ways of reducing the loads from other sources such as: Reduce applied loads from finishes. A 75 mm thick normal weight screed has a weight of about 1.8 kn/m 2. This could be replaced by a lightweight screed, at about 1.2 kn/m 2 or removed completely if not structural and replaced by a raised floor at about 0.5 kn/m 2. If space is not required for services, a resin-based screed could be used, though this could lead to possible problems with levels at doorways, lifts, etc. Replace non-structural block walls with lightweight partitions. In many cases this will be the natural result of the move to open-plan offices. This could reduce the partition loading from 1.0 kn/m 2 originally allowed for to about 0.5 or 0.6 kn/m 2 as suggested in section 3.2.5, or it could be used to argue for the reduction in specified imposed loading from 4.0 kn/m 2 to 2.5 kn/m 2. Ensure all services are supported close to columns. This will reduce bending loads in beams. Remove false ceilings to expose the slab soffit. This will reduce the dead loading by about 0.15 kn/m Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

77 SOLUTIONS TO STRUCTURAL PROBLEMS/OBSTACLES SECTION 6 Increasing the weight of cladding will lead to a possible need to: strengthen existing perimeter beams or create new ones, or increase torsional resistance of existing perimeter beams. Finally, if the structure is being assessed for the effects of increased wind loads, there may be a requirement for increased lateral stability Increasing the capacity of floors and beams Increasing the geometry of beams The strength of a beam may be increased by increasing either its depth or its breadth and by providing additional reinforcement. Although increasing the breadth is the less efficient option it may be preferable to increasing the depth, which could lead to problems with headroom. In both cases it will be necessary to prepare the surface of the existing concrete to ensure good shear transfer into the new concrete. Additional shear reinforcement will be required, enclosing the new tension reinforcement and ensuring that it acts homogeneously with the original beam. The load capacity of slabs may be increased by the construction of secondary beams to reduce the bending moments. However, this will only be appropriate in situations in which there is no conflict with headroom, or the position of services, and in which the ends of the new beams can be adequately connected into the supporting structure. External support systems Various solutions have been proposed for providing external support to members. One approach is to use external prestressing cables (steel or fibre based) with suitable attachments to the sides of beams or kingposts to the soffits of slabs, to reduce deflections [84] but end anchorage may be a problem [85]. Alternatively unstressed external reinforcing bars [86] could be used, which will be easier to install than prestressed cables. A further, somewhat more radical approach, is to use a vertical tension system to carry loads to more lightly loaded floors or to an independent support framework [87], though this will only be applicable if space is available above the under-strength member. Steel plate bonding Steel plates are now regularly used to strengthen concrete beams and slabs, generally being bonded to the soffits to improve the load-carrying capacity [88]. The first application in the UK was in London in BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 65

78 SECTION 6 SOLUTIONS TO STRUCTURAL PROBLEMS/OBSTACLES Fibre composite plate bonding While steel plates continue to be used, advanced fibre-reinforced polymer composites are now being developed as alternative materials for strengthening buildings and other structures although no design codes currently exist, for examples see Flexural strengthening of concrete beams with externally bonded FRP reinforcement [89] and Nonmetallic (FRP) reinforcement for concrete structures [90]. Work on design procedures has, however, recently been carried out in Canada [91]. This paper considers the design of reinforced concrete elements strengthened with fibre composites. It is essentially a design guide for flexural and shear strengthening and includes an iterative design flowchart and a worked example to achieve correct plate thicknesses avoiding failure due to bending or shear of the whole element, or debonding of the fibre composite strip, or ripping of the concrete. The theory is based on the Canadian reinforced concrete design code, but could be easily adjusted to complement BS8110 [53]. There are a number of advantages of carbon fibre plate bonding, including ease of handling and application and minimal additional weight applied to the structure. Carbon fibre reinforced polymer composite strips have been used to strengthen balcony slabs in Germany to overcome problems due to deflections caused by insufficient steel reinforcement [92]. In Italy carbon fibre strips have been bonded in two directions to both faces of a prestressed double curvature concrete shell roof structure. The structure had been damaged, resulting in the loss of some of the prestress; conventional repair techniques were deemed not to be appropriate. Carbon fibre strips were also used to strengthen the main roof beams of an exhibition building, increasing both the flexural and shear capacity. The ground floor beams of a residential building, which had been damaged by an earthquake, were repaired by the use of carbon fibre sheets wrapped round and bonded to the concrete. Carbon fibre composite strips have also been used in various applications in a number of other countries, including Austria, Belgium, the Czech Republic, Hungary and New Zealand. They are now becoming popular in the UK with manufacturers offering a design and installation service. The following are examples: 66 Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

79 SOLUTIONS TO STRUCTURAL PROBLEMS/OBSTACLES SECTION 6 Example of carbon fibre bonding: Wormsley Library, Oxfordshire (Courtesy of Concrete Repairs Ltd) It was necessary to remove a load-bearing wall supporting a floor above in order to create a passage for new services. Removing the wall to create the desired 2 m clear span for the new services imposed an additional loading onto the above floor slab of 75.6 kn/m dead load and 9 kn/m imposed load. The building was constructed in the 1980s with grade C40 reinforced concrete floor slabs 250 mm thick. Carbon fibre strengthening of the floor slab (with the Sika CarboDur system) was utilised to achieve the 2 m clear span and accommodate the increased loading resulting from the removal of the supporting wall. The total cost of the carbon fibre strengthening installation was 5,000. The alternative solutions considered were: 1. steel or RC beams to span the 2 m gap 2. steel plate bonding. Option 1 was discounted immediately due to resulting loss of headroom. Option 2 was discarded in favour of the lightweight carbon fibre strips for ease of handling, speed of installation and thus minimisation of disruption. Example of carbon fibre plate bonding: Normanby College, King s College Hospital, London [93] (Courtesy of Concrete Repairs Ltd.) As part of the refurbishment of Normanby College for King s College Hospital, it was required to add an extra floor on top of the concrete roof slab. The slab therefore needed to be strengthened to carry the additional loadings. The roof was a reinforced concrete ribbed slab with 400 mm deep ribs at 600 mm centres. The span was approximately 11 m and the overall length about 70 m. The building was constructed in the early 1970s. Carbon fibre composite strips (Sika CarboDur system) were bonded to the bottom of the ribs, which doubled the live load capacity of the slab. Before bonding, the concrete was prepared and any small areas of defective concrete made good. The strengthening work took about 4 weeks at a cost of approximately 60,000 (ie. about 80/m 2 or 7/ft 2 ). Steel plate bonding was considered as an alternative, but was rejected for a number of reasons, including: the 11 m span would have required splices steel would have been difficult to handle inserting the required bolts into the narrow ribs would have almost certainly damaged the main reinforcement. In addition, a supplementary support structure was considered but rejected because of limited space. BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 67

80 SECTION 6 SOLUTIONS TO STRUCTURAL PROBLEMS/OBSTACLES The detailed case study of the Allders department stores included in Section 7 is also a good example of carbon fibre reinforcement. Elsewhere in the UK, the material has also been used to strengthen precast stair treads which had been installed the wrong way up. Strengthening will, in general, only increase the live load capacity of the structure, so work should be carried out when the applied load is as low as possible. Methods for prestressing carbon fibre plates are being developed to improve the load carrying capacity. Removal and replacement If floor slabs are significantly under-strength but the supporting beams are adequate, consideration should be given to local demolition and replacement with higher grade concrete and a greater percentage of steel. Alternatively, it may be possible to replace the existing floor slabs with a more efficient system, eg. replace a solid slab with a hollow core slab, which could be used as part of a cooling system. Beam and pot floors, consisting of precast prestressed beams with solid or voided inserts, are widely used in the domestic market but can be used for commercial loads when the spans are limited. Their major advantage in refurbishment work is that the units can be manually handled and are ideal where access is restricted. See also Section on demolition of prestressed elements. The load capacities of various different types of concrete flooring systems, with appropriate spans and depths, can be found in Economic concrete frame elements [94] Increasing the shear capacity of beams at supports Adding external stirrups The traditional approach for increasing the shear capacity is to use external stirrups, suitably encased in additional concrete. The stirrups have to be fully anchored in the compression zone of the beam. In practice, this may mean connecting the stirrups to a strap running across the top of the beam. If the beam is integral with the slab, holes will have to be drilled through the slab to accommodate the shear reinforcement, taking care to avoid cutting any existing steel. Techniques have been developed using steel plate bolted to the sides of beams [95] to increase both the flexural capacity and the shear capacity. Fibre composite wrapping As an alternative, techniques using fibre composite material wrapped round the beam are being developed [96]. 68 Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

81 SOLUTIONS TO STRUCTURAL PROBLEMS/OBSTACLES SECTION Increasing the punching shear capacity around columns Adding a mushroom or down-stand The traditional approach for increasing the punching shear capacity is the provision of a mushroom or down-stand around the column. However, this may cause problems with service runs. The surface of the existing concrete of the column will have to be suitably prepared to ensure effective shear transfer from the new concrete. It may be necessary to drill the column and insert dowel bars to improve the shear transfer. Care will have to be taken to ensure that the new concrete is in contact with the soffit of the slab. The construction of a mushroom or down-stand may be difficult, because of limited access for example, and hence it may be appropriate to consider the use of a fabricated steel shear head which would be clamped to the column. Increase tension steel in slab An alternative approach is to increase the strength of the slab by increasing the tension steel in the region of the column. The traditional approach would be to break-out the concrete down to the level of the tension steel, tie in additional reinforcement and recast the concrete. A large area of break-out would be required, to ensure that the new reinforcement was adequately anchored beyond any potential shear plane. This could result in structural problems during the strengthening process; the floor would have to be propped to avoid any risk of collapse. Hence techniques are being developed which are less disruptive, requiring no breaking out of the concrete. Examples of steel plate bonding: Office building, Leeds [97] In 1985 steel plate was bonded to the top surface of floors in an office building in Leeds to improve the punching shear resistance around columns. Computer room, Reading [98] More recently steel plates were bonded to the top surface of the concrete slab of a computer hall in a building in Reading to increase its load-carrying capacity from 5 kn/m 2 to 12 kn/m 2. The alternative to steel plates would have been the addition of a structural screed, up to 75 mm thick; it was considered that this would add too much weight to the existing structure. Fibre composite plates As an alternative to steel, fibre composite plates could be used, as discussed earlier. Using either material, the headroom would not be significantly affected and the thickness could be easily accommodated in the floor screed or within a raised floor. BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 69

82 SECTION 6 SOLUTIONS TO STRUCTURAL PROBLEMS/OBSTACLES Increasing the load capacity of columns Constructing a concrete jacket around the column The traditional approach involves constructing a concrete jacket around the column, with additional longitudinal reinforcement and shear links. This, however, reduces the net lettable floor area. It will be necessary to ensure composite action between the existing column and the jacket by providing shear connectors. Adding structural steelwork As an alternative to constructing a concrete jacket it has been proposed that confinement to the column may be provided by means of welded steel cages or steel strapping [99]. However, any exposed steel will have to be suitably protected to ensure durability and fire protection. Adding structural steelwork Example of additional structural steelwork: Vantage West, London [100] Two solutions for strengthening the columns in a 1960s office building were considered. The first was to construct a new concrete jacket around the existing columns and the second was to bolt structural steelwork sections to the sides of the existing columns. The second option was chosen for advantages to the programme and so that the floor extension steelwork could be connected to the additional column steel. Fibre composite wrapping Wrapping the column with fibre composite (either glass, carbon or aramid) significantly increases the column capacity [101]. This is most effective on circular columns, but is less effective for square/rectangular columns. Much of the early development work on fibre composite wrapping techniques was carried out in Japan and the USA. The initial aim was to develop cost effective retrofitting for columns, and similar structures such as chimneys, to increase their seismic resistance. More recently the approach has been used to repair columns damaged by reinforcement corrosion as well as to upgrade them. In the UK a major programme of work on column strengthening is being carried out at Southampton University. There have been a number of applications worldwide. In Canada glass fibre-reinforced polymer composite shells have been bonded to the surface of damaged columns to improve their load carrying capacity. In Japan and the USA columns have been strengthened following earthquake damage by wrapping them with carbon fibre-reinforced polymer material, either in the form of a thin strip or in sheet form. Similarly, columns have been strengthened by wrapping them with aramid fibre tape bonded to the surface. The materials are generally applied by hand, though specialist machines have been developed. These are clamped to the column and a carrier head revolves around the column, laying down a continuous fibre tape under tension. The machine gradually climbs up the column, as the required thickness of fibre is installed. 70 Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

83 SOLUTIONS TO STRUCTURAL PROBLEMS/OBSTACLES SECTION 6 Further details about column strengthening can be found in Jacket retrofitting of reinforced concrete columns [102] Increasing the moment capacity at supports Additional reinforcement Increasing the moment capacity at the supports will lead to reduced deflections and increased beam capacity. The traditional approach would be to cut chases in the concrete and bond in additional steel reinforcement across the joint. It must be ensured that the secondary steel is reinstated and anchored adequately. Anchorage of the additional reinforcement into the concrete would be by mechanical anchors or chemical/resin anchors. Welding to the existing reinforcement is an option that is dependent on the carbon content of the steel. Old steel is not suitable for welding as it does not contain enough carbon. A sample of any steel that is to be considered for strengthening by welding-on additional steel should be sent to a specialist laboratory to assess whether it is suitable. Use of fibre composites Techniques are being developed using fibre composites. Example of fibre composites: Parking garage, Florida [103] The beam column connections were strengthened by bonding carbon fibre sheet material to the sides of the beams. This approach was chosen in preference to the conventional solution of increasing the size of the connection by dowelling-in additional steel reinforcement and encasing the joint with additional concrete. It was estimated that the adhesively bonded repair was 35% cheaper than the conventional method Increasing the lateral stability It may be necessary to increase the lateral stability of the building as a consequence of increased wind loading, for example due to the construction of an additional storey. In addition, strengthening measures will be required when there have been major changes to the plan geometry of the building, such as partial demolition to create an atrium. In all cases it will be necessary to ensure that there are adequate vertical and horizontal ties: this will be particularly important for buildings containing precast elements. It should be noted that the requirements for ties now apply to all buildings and not just those of 5 storeys or more, as in previous regulations. Moreover, large-panel 1960s and 1970s buildings were not always tied laterally and this was the cause of the collapse of the Ronan Point block of flats in Bringing such buildings up to modern day standards should be considered. This will be mandatory under the Building Regulations if the building is to have a change of use. BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 71

84 SECTION 6 SOLUTIONS TO STRUCTURAL PROBLEMS/OBSTACLES Use of unstressed prestressing strand Consideration should be given to the use of unstressed prestressing strand to form any ties that are required. Long lengths are available so that it can be readily installed continuously through the length or height of the building. Add steel cross-bracing Steel cross-bracing could be added and would not reduce the lettable floor area. Increase thickness of existing shear walls or construct new walls Provided space is available, the most straightforward way of increasing stability is likely to be to increase the thickness of the existing shear walls and the walls of staircases and cores. This can be achieved by casting an additional concrete skin, adequately tied to the original wall, or by the use of sprayed concrete. If existing walls cannot be thickened it may be necessary to form new shear walls, adequately tied into the frame of the building. Both techniques will increase the dead loading on the building and reduce the net lettable floor area. Example of increasing wall thicknesses: 338 Euston Road, London [66] The two existing RC stair towers were strengthened by adding extra layers of reinforced concrete. This was achieved by bolting high tensile steel rebars to the outside faces of the towers and subsequently spraying concrete onto them. Use of fibre composites Alternatively, existing non-load bearing blockwork walls could be stiffened, eg by bonding on carbon fibre composite strips, to form shear walls [104]. This leads to a negligible increase in the wall thickness. One reported application, used to strengthen a building damaged by an earthquake, showed a 30% cost saving over traditional repair techniques. Some increase in lateral stability can be achieved by increasing the moment capacity at supports, as described in Section Increasing the load capacity of the foundations If significant additional loads are to be applied to the structure, the load capacity of the foundations will have to be assessed (see section 3.2.1). Extra load capacity is generally built into the foundations of older buildings and in the 1970s District Surveyors would commonly allow an additional 10% of the total building loading (approximately equivalent to one additional floor) to be added to the foundations at a later date, provided the building was sound and no settlement had occurred. This does not preclude a load capacity assessment, however. 72 Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

85 SOLUTIONS TO STRUCTURAL PROBLEMS/OBSTACLES SECTION 6 If required, the capacity of the foundations can be increased in the following ways: Increasing existing footings Simple raft, pad or strip footings may be increased by casting additional concrete. Care must be taken to ensure adequate shear transfer between the old and new concrete, by roughening the surface and by the use of dowels. The added concrete may only function once additional movement of the building has occurred. Addition of new piles If access is not a problem, additional piles may be installed, using conventional equipment, around the periphery of the building. There are a number of systems for installing mini-piles inside a building, often in situations where headroom is limited. Again, new pile caps, or capping beams, will have to be adequately tied into the existing members. Because the new piles, or footings, will only carry the increase in loading, and hence may not be acting efficiently, consideration should be given to installing flat jacks, which could be used to transfer the load from the old structure to the new. This would remove possible problems of differential settlement between the new and old foundations. Underpinning Underpinning of the structure or adjacent structures may be necessary in areas of settlement and loss or degradation of subsoil. This may also be used to enhance the load carrying capacity of the foundations Summary of methods for increasing load capacity Table 15 summarises the possibilities for structural strengthening that have been detailed above. BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 73

86 SECTION 6 SOLUTIONS TO STRUCTURAL PROBLEMS/OBSTACLES Table 15 Structural strengthening options Slabs Beams bending Beams shear Slabs punching shear Columns compression Support regions Increase geometry External support system Steel plate bonding Fibre composite plate bonding Removal and replacement Addition of external stirrups Fibre composite wrapping Add mushroom downstand Additional reinforcement Construct jacket Add structural steelwork Additional ties Pre-stressing strand Increase wall thickness/add walls Increase footing size Add piles Under-pinning Frame stability Foundation 6.3 SPATIAL CHANGES The following sections describe the ways in which the geometry of a concrete building can be modified to suit refurbishment requirements. Modifications to a building s geometry affect its structural integrity and it is therefore important that schemes are checked by a qualified structural engineer Limited storey height A limited storey height leads to problems with the provision of services in a restricted space. One solution is to remove false ceilings and use the exposed concrete slab soffit directly or with a suitable thin decorative coating. However this can cause problems with sound transmission. Alternatively, it may be possible to lower the level of raised floors. One limitation will be when drainage runs are required to pass below the raised floor. It may be possible to remove thick sand-cement screeds and replace with thin resin-based screeds if the screed is non-structural. This has the added advantage of making a higher floor loading possible. It should be noted that altering the floor height will cause problems with door openings, access to lifts, staircases etc. This could cause difficulties with access for disabled people Removal of a column The removal of a column will cause major structural problems. Hence, it can probably only be justified in very limited situations, such as creating an open space in an entrance hall. 74 Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

87 SOLUTIONS TO STRUCTURAL PROBLEMS/OBSTACLES SECTION 6 The traditional approach is to construct transfer beams to carry load to adjacent columns, though this could lead to possible problems with service runs. It may be possible to partially relieve the load originally carried by the column by increasing the moment capacity at adjacent supports. Before the existing column is demolished, it will be necessary to ensure that the load carried by the column is transferred to the new structure, for example by using flat jacks. Example of column removal: Vantage West, London [100] Here a new transfer beam was constructed at a higher level to transfer the intermediate column loads to the main columns. The reference describes the sequence of work and the falsework necessary for the removal of intermediate columns to allow freer access. As an alternative, a vertical tension system could be used to carry loads to more lightly loaded floors or to an independent framework [87] or external prestressing could be added to carry the loads originally carried by the column, with appropriate brackets on the sides of the beams. There may be a need to provide additional tension steel at the location of the former column. NatWest Tower, London [105] Built in 1981 with slipformed in situ concrete, the NatWest Tower was bombed in 1993 and therefore required major repairs and refurbishment. The opportunity was taken at this time to extend the floor slabs into the space previously occupied by services, thus increasing the lettable floor area by 8.5%. The existing floor slabs were broken back so that new rebars could be tied to the existing reinforcement and in situ concrete cast. The new extensions are supported by new steel beams fixed to existing columns. The external services were replaced by new services located in raised floors and false ceiling corridors. Recladding of the complete building was also carried out Creating openings in slabs The approach adopted will depend on the form of construction, ie in situ slab or precast units. A useful rule of thumb is that with reinforcement trimming, a slab can accommodate holes of an area up to 10-12% of the total area of the slab without the structural integrity of the member being compromised [106]. Small holes up to 75 mm or more may easily be accommodated in precast slabs, depending on the size of the voids between the reinforced webs and provided the holes do not disturb reinforcement. If possible, guidance should be sought from the unit manufacturer. If a larger hole is required within precast slabs, it should be relatively easy to cut out a length of slab, or remove it in total, in the required region and support the remaining portions of the slab by means of a cradle or suitable brackets. Again the manufacturer s advice should be sought and the ability to transfer load to other members should be checked. Obviously there is a need to accurately determine the position of any reinforcement or prestressing before carrying out any work. Precast pre-tensioned BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 75

88 SECTION 6 SOLUTIONS TO STRUCTURAL PROBLEMS/OBSTACLES units can be cut without further problems as the tendons will be fully bonded and the unit will perform as a conventional reinforced element, except that there will be a local loss of pre-stress where the unit has been cut. Particular care will be required when cutting into post-tensioned prestressed slabs or units [107], although creating small openings in posttensioned floors with unbonded tendons will not be a problem, provided the hole can be located between the tendons. The maximum dimension that can be readily accommodated will obviously depend on the tendon layout. Where it is necessary to form a larger hole, severing unbonded post-tensioning tendons, the tendons crossing the affected area will have to be carefully de-stressed, the hole cut in the slab and then the tendons re-stressed with new anchors at the edge of the hole. An outline example of the sequence of work is given in Post-tensioned concrete floors in multi-storey buildings [14]. Refer also to Section Any scheme should be checked by a qualified structural engineer. With waffle or ribbed slabs cast in situ, holes may be cut through the slab without having any significant effect on the load carrying capacity as all the tensile reinforcement is located in the ribs. If it is necessary to cut through the ribs the same procedures described for precast slabs will apply. Mushroom head slabs should not have holes cut in them as the load capacity would be reduced to an unacceptable level. This is also likely to prove impractical. Flat slabs generally have reinforcement spaced at mm and can therefore accommodate small holes up to about 100 mm. The most critical zone tends to be at the columns where there is the risk of punching shear and the remaining shear capacity should be checked. Creating openings in slabs cast in situ which involves the severance of reinforcement requires the fixing of additional reinforcement around the sides of the opening to replace that lost. Guidance for this is given in the Concrete Society Working Party Report [108]. Alternatively, a traditional method is to bond steel plates to the slab soffit, but this approach has limitations. Carbon fibre strips are being used, because of the ease of handling and application. Examples of creating openings in slabs: Shopping centre, Winterthur, Switzerland [92] Extensive strengthening of the floor slabs was required so that openings could be cut in the 350 mm thick slabs to allow for the installation of new lifts and escalators. Carbon fibre-reinforced polymer composite strips were bonded to the soffit in both directions on either side of each opening. Department stores, UK The same approach has been used to provide additional reinforcement around newly created openings in floor slabs required for escalators in two department stores in the UK, see Case Study Page Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

89 SOLUTIONS TO STRUCTURAL PROBLEMS/OBSTACLES SECTION Creating openings in beams and walls Small holes in beams and walls will not affect the load capacity. How large a hole can be tolerated will depend on the member under consideration. The key requirements will be to locate the hole in areas of the low stress, such as at the neutral axis of a beam, and to avoid cutting any reinforcement. If the size of the hole is such that cutting reinforcement is unavoidable, then the approach should be as for slabs, ie. any lost reinforcement needs to be replaced, possibly by plate bonding. It is generally preferable to cut any necessary holes through slabs rather than beams as the reinforcement in beams is more closely spaced than in slabs, and beams include shear reinforcement whereas slabs do not. Shear walls must be checked for structural integrity if holes are to be cut, and an independent support system may be required Demolition of prestressed elements Great care must be taken when demolishing post-tensioned concrete elements. Pre-tensioned elements generally behave in the same way as ordinary reinforced concrete as the tendons are fully bonded to the surrounding concrete. However, the tendons in post-tensioned elements, which are unbonded or where the grouting is inadequate, store a great deal of energy which, if released suddenly, pose a potential safety hazard to personnel and property in the vicinity. Identify whether the element is prestressed Refer to BS 6187 [109]. The following may indicate whether an element is prestressed: reference to record drawings the presence of a special building plaque on the structure dimensional and strength characteristics the presence of anchors for post-tensioning. Pre-tensioned elements Comprehensive guidance on the demolition of pre-tensioned structural elements is given in BS Beams and slabs up to a span of 7 m can generally be demolished as ordinary reinforced concrete. Otherwise, members should be removed intact from the structure and broken up on the ground. Temporary support should be substituted whilst large members are broken out in situ. Post-tensioned elements The British Standard gives little guidance on this aspect. In general, tension in unbonded (ungrouted) tendons should be able to be released gradually at the end anchorages. For members with bonded (ie. grouted) tendons, the adequacy of the bond cannot be ascertained and there is a high risk of the presence of air pockets which could cause a sudden shock release if the tendons are disturbed. In the case of small elements, such as slabs, it may be possible to apply heat to the ends of the tendons so that the stress is reduced first by relaxation due to BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 77

90 SECTION 6 SOLUTIONS TO STRUCTURAL PROBLEMS/OBSTACLES expansion. Reference can be made to Post-tensioned concrete floors in multi-storey buildings [14] for general guidance. A good set of guidelines for the demolition of large post-tensioned elements is available in Controlled demolition of a post-tensioned beam [110] where the demolition of a large beam was planned and monitored. A summary follows: 1. If the prestressing system can be identified, advice should be sought from the manufacturer. 2. Accurately locate tendons with a metal detector and cover meter. 3. Working drawings detailing temporary works and the procedure for releasing the prestressing forces are essential (and mandatory now under the CDM Regulations). 4. The effect of the demolition on adjacent members should be considered. 5. The temporary supports must be capable of withstanding the full design load. 6. Cover the ends of the beam with steel plates strapped in a harness of Macalloy bars and anchor blocks. 7. The tendon cutting procedure should follow similar principles to those shown in Figure 10 and should be carried out symmetrically. The sequence allows the cutters to stand clear after the last tendons are cut. 8. Use a small pneumatic breaker to cut away the concrete for access to tendons 3 and The tendons should be cut with oxyacetylene torches. 10. After the tendons are cut the stress transfers to the Macalloy bars which can then be released slowly by unscrewing the nuts at the anchor plates. Figure 10 Tendon cutting sequence Another useful reference concerns the demolition of the post-tensioned beam-supported Marks and Spencer building in Manchester following the 1996 bomb attack [111]. 78 Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

91 SOLUTIONS TO STRUCTURAL PROBLEMS/OBSTACLES SECTION Creating an atrium by partial demolition If part of the existing building is to be demolished, for example to create an atrium, it will be necessary to check carefully the structural behaviour and the stability of the remaining structure. The pattern of loading applied to members close to the demolished part will change. For example, internal columns may become edge columns and continuous beams become effectively simply supported. Before undertaking any work the scheme should be checked by a suitably qualified structural engineer, who should consider the stability during the demolition process as well as any strengthening of the remaining structure, see Section Increasing the floor area Two types of floor extension are possible. The first, and more common, is a minimal extension so that services, such as air supply ducts can be located outside the original building line, thus freeing usable space inside the building. The loadings will be relatively light, which will impose little additional loading onto the building frame. The second approach is to construct additional usable floor space, which has to be designed to carry the full floor loading. Examples of minimal floor extension: 20 Cannon Street, London [66] Projecting bulkheads resembling balconies were bolted onto the external faces of the existing perimeter walls to accommodate ducting for the new air-conditioning for this 1960s building. The additional loads were minimal and were accommodated by the existing structure without the requirement for strengthening. The balconies were also used to provide solar shading and access walkways for cleaning and maintenance. Capital House, London [66] Again to accommodate the air-conditioning fan coil units, 300 mm wide floor extensions were formed with dry lining boards which were supported by steel gallows brackets bolted to the existing columns. BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 79

92 SECTION 6 SOLUTIONS TO STRUCTURAL PROBLEMS/OBSTACLES Examples of full load capacity floor extensions: Vantage West, London A system of precast concrete slabs, supported by a steel framework attached to the perimeter columns, provided an additional 750 mm width of floor around the existing structure [100,105]. City Point, London, EC2 Figure 11 City Point stripped back to the frame The 36-storey building has been stripped back to the frame. The floor plates are to be extended by 1 m. The existing 100 mm screed is to be removed and a raised floor (100 mm) added. This will also allow the floor loading to be increased from 2.5 kn/m 2 to 3.5 kn/m 2. The existing floor columns on the perimeter are to be extended. These extended columns have been used as partitions in other refurbishment projects. The limiting factor in any such extension system will be the ability of the columns to carry the increased load. However, even if the columns are under-strength, they can be strengthened using the fibre composite wrapping techniques described above, which should result in floor extension being a cost effective option. A further consequence of extending the floor is that it will increase the area of the elevation of the building, which will increase the wind loading. This may require additional bracing, see Section Care will obviously have to be taken when connecting any new supporting framework to the columns to avoid cutting the reinforcement. 80 Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

93 SOLUTIONS TO STRUCTURAL PROBLEMS/OBSTACLES SECTION Adding an additional floor Adding an additional floor using modern materials such as lightweight concrete floors and lightweight cladding may not add significantly to the total weight, particularly if the roof previously carried heavy plant [66]. In general, the roof slab will have been designed to lower loadings than the floor slabs elsewhere in the building. Hence it may be necessary to carry out some strengthening. An additional floor will increase the wind loading on the structure, which may require additional bracing, see Section VISUAL APPEARANCE The appearance of many old buildings, whether concrete, brick or steel, is poor. This is generally linked to poor detailing. Dirt may be trapped by some surface textures and the geometry of the structure may be such that some areas are not washed clean by the rain, resulting in a mottled or streaked appearance [112]. In major refurbishments the cladding may be replaced but in other cases it will be necessary to give the concrete a face lift. Simply washing the structure will greatly improve the appearance, as has been done with many inner city buildings. In addition, the surface can be painted with a water repellent coating which will have the added advantage of improving the durability. Patch repairs will be necessary if there is rust staining or local spalling of the concrete due to corrosion of reinforcing bars with inadequate cover. The concrete should be broken back to behind the reinforcing steel, the steel cleaned and treated to stop corrosion, and the area made good with a cement-based or resin-based mortar [113]. Generally, it will be difficult to match the appearance of the patch with that of the parent concrete, so it will again be necessary to paint the surface (see Section 6.1 on concrete repair). Examples of refurbishment of cladding and other exposed concrete surfaces are given by Tackling a high rise refurbishment problem [114], Long life coatings combat the high rise refurbishment problem [115], and UK's largest concrete refurbishment completed [116]. 6.5 BASEMENTS There may be a requirement to upgrade basements, for example following a change of use from a plant room to a storage area. Efficient waterproofing will be essential, particularly with rising ground water levels in many cities. There are a number of different approaches, including systems applied to the surface of existing walls and the construction of an inner wall, with a drained cavity [117]. Water-resisting basements [118] and Water-resisting basements (Summary report) [119] also give guidance on safeguarding new and existing basements against water and dampness. 6.6 CLADDING It may be desirable from an aesthetic or architectural point of view that the existing cladding is removed and replaced with new. If, however, the cladding is to remain, the condition of cladding panels and the fixings used to attach the cladding to the frame of the building should be inspected and replaced as necessary. BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 81

94 SECTION 6 SOLUTIONS TO STRUCTURAL PROBLEMS/OBSTACLES The inspection should be carried out by a suitably qualified specialist. Broken or badly damaged cladding panels should be replaced. Problems that may be encountered with fixings include: inadequate, deteriorated or damaged fixing brackets inadequate, deteriorated or damaged anchors inadequate, deteriorated or damaged substrate inadequate number of fixings movement in the cladding panels. The examination of the fixing system should be carried out from the outside and also internally where blockwork, insulation or other obstacles may have to be removed. The condition of the sealing material around individual cladding units should also be checked; this will have a limited life and may need replacing. Once the problem has been diagnosed remedial works can be designed and put in place. These tasks should be carried out by a competent facade engineer. More details and an example of failure of cladding fixings is included in Failure and rectification of fixings of large precast concrete cladding units [120]. 82 Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

95 CASE STUDIES SECTION 7 7 CASE STUDIES 7.1 INTRODUCTION This section details several case studies concerning refurbishment of building services and structures. The case studies demonstrate a range of technical issues in both high profile and more typical buildings and demonstrate the practicality of reviving old concrete buildings. Cost details are provided where available. 7.2 BUILDING SERVICES Case study 1 - Howard House, Bristol Conventional concrete office building undergoes services refurbishment to improve lettable value (Courtesy of Sure Foundation Building Services Engineers) Background The refurbishment of Howard House was brought about due to the building services reaching the end of their 25 year life. As much of the existing services ductwork and some plant was able to be re-used, and floor loadings were not varied significantly, no major structural work was necessary. Originally the building was comfort cooled via a low level perimeter induction system. However, the capital cost of replacing this cooling system and the on-going service costs could not be justified by the office rents obtainable in Bristol. Form of construction The building was constructed in The seven-storey structure provides a total floor area of approximately 31,000 ft 2 It is an in situ concrete frame structure with columns on a 4.8 m grid. The cladding consists of precast concrete panels and double glazed windows. The building was not insulated at the time of its original construction. Overall the building is structurally of a high quality. BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 83

96 SECTION 7 CASE STUDIES The solution Due to the financial preclusion of replacing the air conditioning, it was decided that the building would be heated only, with a combination of natural ventilation via existing openable windows and a quasidisplacement ventilation system. This made use of existing ductwork which was routed, via columns 4.8 m apart, to the original perimeter induction units. The induction units were removed and displacement type swirl diffusers fitted in a vertical plane at the point where the supply ductwork exited from the column. Two additional supply grilles were fitted in the ceiling at the deepest part of the floor plan to provide additional ventilation. Air extract is via the light fittings into the ceiling void plenum. A DX unit was fitted to the supply duct to provide comfort cooling under on/off control. A two speed supply fan provides nominal air change rates of two air changes per hour in the daytime and four air changes per hour at night. The lesser daytime air flow rate is due to the noise problems expected with higher air flow rates. The unoccupied building is to be pre-cooled at night using free air cooling. Thermal modelling was undertaken to verify the basic design intention. The existing windows were modified to enable a 250 mm opening to be achieved instead of the original 100 mm. When the existing air induction units were removed, the net lettable floor area was increased by approximately 2,000 ft 2, some 6.5% increase. Insulation was added to the external walls to meet current Building Regulations. Solar shading is provided by the existing tinted glazing and by virtue of shading created by adjacent buildings for much of the day. The installation of internal blinds has been recommended as part of the tenant fit out. However, one tenant was concerned about the loss of air conditioning and employed an independent consultant to investigate the issue further. The conclusions of this independent study agreed with the original design proposal that the building would operate satisfactorily without mechanical cooling. A raised floor was not fitted. New bespoke floor boxes were added and the power and communications wiring to them was renewed. Additional perimeter power trunking was added. The fire alarm system was replaced with an analogue addressable fire system. New heating plant and distribution systems were fitted and the lifts were cosmetically refurbished. 84 Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

97 CASE STUDIES SECTION 7 Figure 12 View of stripped-out floor Structurally, little was modified, although, the column casings were removed and subsequently replaced in order to modify the ductwork within them. False ceilings were added to cover the defective appearance of slab soffits. Some chasing in walls and floors was necessary. Alternative approaches considered The use of fan coil units and variable refrigerant volume cooling were also considered. Exposing the concrete ceiling was considered but the condition of the ceiling prevented this. Cost The approximate cost of all the refurbishment work was 25/ft 2 ( 270/m 2 ) Client Dorset County Council Pension Fund developer and financier Architect King Sturge were the building agent, client s project manager and architect Designers Sure Foundation Building Services Ltd Latter Ramsay Partnership structural engineer Quantity Surveyor Ashley Associates Main contractor RSW plc (Restoration South West) Specialist sub-contractor BSRIA thermal modelling BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 85

98 SECTION 7 CASE STUDIES Case Study 2 - Boots D10 building, Beeston, Nottingham (Courtesy of AMEC Design and Management and Boots Ltd.) 1930s concrete factory partially converted to office accommodation, the rest remaining as manufacturing areas. Photograph courtesy of Martine Hamilton Knight Background This factory building, completed in 1933, required complete refurbishment of the services, especially in the office areas adjacent to the fully glazed southern facade which were prone to over-heating in summer and over-cooling in winter. The opportunity was taken to add a raised floor in the office area. The thousands of glass prisms in the roof required water proofing and there was a need to replace the facade, which could not practicably be repaired. Form of construction Completed in 1933 the main features of this four storey building are large mushroom-head reinforced concrete columns (which incorporate service holes in the head ) and flat slabs, both of which exhibit original board marks as created by the shuttering. Drop-in slabs were used to aid installation of large equipment especially large storage vessels. Four large light wells allow natural light to light the main factory production area on the ground floor. The long front elevation of the building is south facing and fully glazed. The solution Structurally, little change was made. The appearance of the facade has been fully maintained despite its complete replacement - a requirement of English Heritage that involved protracted consultation. The glass is now double glazed rather than the single glazing originally used. Internal blinds have been added. The building services remain exposed beneath the slab, although the pipework is clad to make it more aesthetically appealing. The exception is the sprinkler pipework which has been painted red and follows the contour lines of the concrete slab, actually accentuating the line of the internal structure. The refurbishment took place in stages, which caused some major problems. All pipe and ductwork routes had to be traced since areas undergoing refurbishment contained services to areas that were still operational. A 86 Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

99 CASE STUDIES SECTION 7 further problem related to the removal of the concrete screed in the second floor office area to allow the fitting of the raised floor. This screed had been added to allow in-floor drainage for the laboratory area. The screed varied in thickness from 75 mm to 225 mm and required much effort in its removal. The internal factory area is ventilated using air infiltration and opening windows on facades remote from the main working area, except for some small process areas fitted out subsequent to the refurbishment which have been fully enclosed and provided with full air conditioning. The office and laboratory areas are comfort cooled using local cooling plant. The external exposed concrete of the building necessitated only minor repairs and was coated to provide weather protection. This had previously been undertaken in the 1970s and had contributed to the durability of the external concrete. One benefit with this building is that the floor loadings were not an issue due to the strength inherent in the building design. Cost The approximate capital cost for the refurbishment work, including structural work and M&E services equated to just over 1500/m 2 at 1994 rates. Client Boots Contract Manufacturing Architect, Structural Engineer, Services Engineer, Quantity Surveyor, and Main Contractor AMEC Design and Management Reference Factory with a facelift [121] BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 87

100 SECTION 7 CASE STUDIES Case Study 3 - DTI Building, London Improved internal environment and 25% increase in net floor area Background This 50,000 m 2 building was built in the early 1960s and consists of two sections of five and eight stories. It is aligned on an approximate NE/SW axis and suffered overheating causing occupant dissatisfaction. The single glazed windows were un-openable. Reflective solar film had been applied to the windows in an attempt to reduce heat gains but this created a dim interior. In addition, the dual duct air conditioning system conditioned large volumes of air and was very inefficient. The plant, situated in the basement plant room, drew air of poor quality from street level. The building has low floor to ceiling heights and the underfloor trunking was inadequate to provide a reasonable IT network. Solution The primary objective was to improve the internal environment whilst keeping operating costs to a minimum. The original glazing was retained, avoiding any planning issues, and double glazing was added internally thereby creating a cavity in which a motorised solar blind was installed. These blinds are under automatic control with manual override, allowing early morning solar gains prior to occupation to be minimised, as well as containing the amount of solar gain on the hottest days of the year when the blinds must be down to prevent the building from overheating. The cavity between the windows is ventilated to prevent heat build up. Lighting was also placed under automatic control with a philosophy of manual switch on, automatic off. This helps to minimise internal heat gains. Cooling is provided by chilled ceilings which cover all office areas. This maximises the floor area and allows for easy alteration of the partition layout. The chilled ceiling has been incorporated in a shallow ceiling void of 225 mm allowing a 200 mm raised floor to be provided for cable distribution whilst still leaving 2.7 m floor to ceiling height. Heating is provided by simple hot water radiators beneath the windows. Fresh air ventilation is provided both passively, via trickle vents in each window, and actively via variable flow mechanical displacement ventilation under the control of CO 2 and temperature sensors in the space. Reduction in supply air volumes with the displacement system allowed all the ventilation plant to be sited on the roof, with the added advantage of a cleaner air supply. This released the basement plant areas which were converted into restaurant and conference space. Replanning of the office and core areas together with a reduction in the oversupply of toilet facilities provided a total net floor area increase of 6,300 m 2, a rise of approximately 25%. 88 Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

101 CASE STUDIES SECTION 7 Cost The total cost of the refurbishment was approximately 46M, which with a gross floor area of 46,500 m 2 (31,000 m 2 net usable office space) equates to 989/m 2 ( 1483/m 2 net). Client Department of Trade and Industry Architect DEGW Services Engineeer Troup Bywaters and Anders Structural Engineer Waterman and Partners Project Manager and Quantity surveyors Gardiner and Theobald BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 89

102 SECTION 7 CASE STUDIES 7.3 STRUCTURAL Case study 4 - Allders Department Stores, Croydon and Portsmouth Escalator added to department store (Courtesy of Sika Limited) Background Carbon fibre bonding above operational area As part of the refurbishment of the Croydon store, two new escalators were required. This necessitated cutting a 10 m x 6 m hole through an existing concrete floor slab severing the beam strip and relinquishing the continuity of the slab to adjacent bays. A major requirement during the work was that the adopted system should cause minimal disruption to the operation of the store. A project similar in concept was carried out in the store at Portsmouth to install a new stairwell but involved less disruption than the project at Croydon. It is therefore the Croydon project that is detailed here. Form of construction The original 1920s building in Croydon was extended in the late 1960s with a reinforced concrete framed flat-slab structure with four storeys and two basement levels. It is this structure that was modified to accommodate the new escalators. The columns of the 1960s building are on a 12.2 m x 8.5 m grid and the 300 mm thick flat slabs span onto the angular heads of the circular reinforced concrete columns. The solution The new escalators were hung off new steel beams spanning between the existing columns. However, the escalator well severed the beam strip and floor slab. Four bays of the remaining slab were strengthened using carbon fibre strips (Sika CarboDur system) bonded around the area to be removed for the new well. In some locations the strips were installed above the existing services, which were suspended from the slab, without any disruption. 90 Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

103 CASE STUDIES SECTION 7 Cost The modifications carried out in the Croydon department store involved 550 m of carbon fibre strips costing 56,000. This equates to a unit cost of approximately 102/m. In the Portsmouth store, where a similar project was carried out, 200 m of carbon fibre strips were used costing 21,950, equating to a unit cost of approximately 110/m. Alternative approaches considered Three alternative solutions to the problem of strengthening the remaining beam strip and slab panels were originally considered by the designer to cater for the additional moment induced by the removal of the adjacent continuous bay: 1. A structural steelwork grillage positioned and pinned below the slab and beam strips, reducing existing spans. 2. Steel plate bonding to the underside of the remaining floor elements. 3. Carbon fibre strips bonded to the underside of the remaining floor elements. Solution 1 was easily dismissed due to the implications for existing ceilings and services in adjacent bays, and the accompanying need for large quantities of steelwork, which would have involved much disruption to the operation of the store. Solution 2 had been used previously at the store on a different floor level some eight years earlier. The scheme was successful given the construction technology available at the time. However, solution 3 had some clear benefits over solution 2 given the increased commercial availability of carbon fibre strips and specialist contractors to install them. The main advantage of using carbon fibre plate bonding over steel plate bonding was the relative ease and speed of installation due to the light weight of the carbon fibre strips compared with the heavier and more cumbersome steel plates. A cost comparison was undertaken for solutions 2 and 3 comprising material and installation costs. This showed that carbon fibre plate bonding was 20% more costly than steel plate bonding. However, this cost disadvantage was eliminated once the whole project construction programme, including necessary services diversions, was considered. The construction programme and disruption to the store operation were minimised with the carbon fibre method as the strips could be installed while some services remained in place. The client was willing to pay the excess since his most important requirement was to minimise disruption and thus maximise income from his business. Designer Thomason Partnership Main contractor Styles & Wood Specialist sub-contractor Concrete Repairs Limited BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 91

104 SECTION 7 CASE STUDIES Case study 5 - No 1 Neathouse Place, Office Building, London Maximisation of lettable space and improvement of office environment (Courtesy of Buro Happold and Chesterfield Properties) Background, reason for refurbishment/alteration and structural problem Built in 1959, No. 1 Neathouse Place had a drab facade, poor air conditioning and too many structural walls for a desirable, modern office building. The client s fundamental requirements for refurbishment were: maximisation of lettable space and chargeable rent improvement of the quality of the office environment improvement of the building s image reversal of the main entrance to the building replacement of the cladding system. Form of construction The building is a 12-storey concrete framed structure with basement, 65 m long by 15 m wide. It spans Neathouse Place at second floor level with a storey-height post-tensioned concrete box girder. The longitudinal column grid was 4.5 m on the upper floor and 7.2 m on the lower floors. Floors were 255 mm thick beam and pot floors. Bookend shear walls running the full height of each end of the building provided lateral stability. Longitudinal stability was provided by the lift core walls and a central spine wall running part of the building length. 92 Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

105 CASE STUDIES SECTION 7 The solution The floor space was maximised in a number of ways. The spine shear wall was removed with vertical support maintained by inserting steel columns into the walls at the main grid lines and spanning beams along each side of the walls to carry the floor above. Horizontal stability was provided by new a vertical steel truss built onto the end of the remaining spine wall prior to demolition of the main part of the wall. Loads were transferred back to the main load-bearing elements by a composite steel and concrete girder. Figure 13 Building stripped back to concrete frame Inner staircases were removed and a new staircase and new plant rooms and toilets were accommodated by building onto the outside of the structure. The construction for this consisted of lightweight concrete holorib floors supported on steelwork, thus contributing little increase in load on the foundations. Further benefit in terms of reducing loadings was obtained by removal of the 60 mm thick screeds on each floor. The glass facade walls are supported on steel sub-frames at each floor level, which span back to existing columns. Recladding the structure in glass gives dramatic views from inside the building, increases light penetration into the occupied floors and provides routes for air extraction along the perimeter of the building at every level. In the original structure extract ductwork ran at ceiling level through a defined corridor zone. To achieve flush ceilings for maximum space planning flexibility a new solution was required. Air conditioning was provided by air treatment modules, which provide high specification air conditioning but which can be located away from the offices so that net lettable area is maximised. Moreover, minimal ceiling void space is necessary for the system. Slots through shear walls were cut for new ducts, achieved by inserting steel cellular beams to carry vertical loads through web stiffener plates between the ducts. BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 93

106 SECTION 7 CASE STUDIES Figure 14 New glazing Other holes for ducts were also required. Some were small enough not to affect the structural integrity and other larger holes were positioned in areas of low stress so that no strengthening was required. In some areas, however, strengthening was unavoidable and was achieved by breaking out the top of an upstand beam to expose the reinforcement, lapping an additional capping beam to connect with the floor above, and thus creating a storey-height reinforced concrete truss. The area below the new beam could then be cut out to accommodate the new services. The prestressed part of the structure over Neathouse Place was not modified. Cost The approximate capital cost for the refurbishment work, including steel, concrete and M&E services, was 18 million, equating to just over 1500/m 2. Alternative approaches considered To maximise full use of the site, the client considered complete demolition of the building and replacement with a new much taller building. However, the proposed new building height raised concerns of wind effects at street level. Moreover, the cost of demolition and rebuild was prohibitive. Demolition would have caused major disruption to the roads and, further, the demolition of the post-tensioned concrete beams spanning Neathouse Place would have presented a safety risk, high cost and an extended programme. Client Chesterfield Properties 94 Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

107 CASE STUDIES SECTION 7 Architect Avery Associates Designers Structural engineer M&E engineer - Buro Happold - YRM(E) Quantity Surveyor Leonard Stace Main contractor Wates Special Works Specialist sub-contractors Cladding - Felix Constructions Main steel - Tubeworkers (Structural) Ltd Rotunda steel - Joy Steel Special steel (staircases) - Crane and Rowbury References No. 1 Neathouse Place [122] Neat and tidy [123] BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 95

108 SECTION 7 CASE STUDIES Case Study 6 - Office to Hotel 1970s office building converted to hotel A 1970s office complex in the centre of a provincial UK city suffered from low rents. The problem was resolved when the owner was approached by a hotel chain suggesting conversion of the building into a budget hotel with 142 bedrooms. The owner was responsible for the development of the building which was then leased to the hotel chain for years. There was insufficient parking for all the hotel guests but this was not perceived to be a problem due to the central location of the building. The main problem was that the structural grid was too small to accommodate the 2.9 by 5.7 m standard bedroom size. This was resolved by modifying the standard room dimensions to a slightly wider but shorter size. The original seven storey in situ reinforced concrete framed buildings, one L-shaped in plan, the other rectangular, were constructed in Precast concrete had been used as cladding and structural panels. The buildings were linked by a bridge at second floor level. Structural columns were spaced at 5.2 m. During the refurbishment work cladding panels were removed so that a new conservatory type lean-to extension could be built onto the rectangular building at ground level. All the internal services were replaced and sewers were all enlarged. Stud partition walls were used in preference to concrete block walls due to their superior noise dampening attributes. Floor loadings were not a problem since the minimum imposed design floor loading for hotel bedrooms and reception areas is 2.0 kn/m 2 whilst the minimum imposed design floor loading in 1974 for offices was 2.5 kn/m 2. Moreover, the actual structure may have been designed to a higher capacity than the minimum, possibly up to 4.0 kn/m 2. The corridors in the hotel should have an imposed load capacity of 4.0 kn/m Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

109 APPENDICES APPENDIX A Legislation Affecting Refurbishment BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 97

110 APPENDIX A A1.1 INTRODUCTION The legislation listed below is intended to indicate some of the main legislation affecting building refurbishment. There are many Acts of Parliament and Regulations affecting buildings and building services. Further, European law is increasingly affecting the UK in the form of European Council Regulations (which come into force in the UK as soon as they are published in the Official Journal) and European Directives (which require the appropriate change to UK legislation before they become law). A more comprehensive list and references to other sources of guidance may be found in Building services legislation [124], the HMSO Monthly Catalogue, The practical guide to EC rules for building services products [125], and SPEARHEAD [126] - an online database of existing and forthcoming European Commission legislation. Regulations published as (UK) Statutory Instruments (SI) from 1997 onwards are available in full text on the Internet. The address is A1.2 GENERAL LEGISLATION Building Regulations 1991 (SI 1991/2768) These Regulations were made under the Building Act Two new Approved Documents were issued under the Building Regulations (Amendment) Regulations 1994 (SI 1994/1850): Part F Ventilation (1995 edition) and Part L Conservation of fuel and power (1995 edition). Some new or revised documents have been published as 1992 editions including Part A Structure (1991), Part B Fire safety (1991), Part C Site Preparation and Resistance to Moisture (1991), Part E Resistance to the passage of sound (1991) and Part G Hygiene (1991). Building Regulation (Amendment) Regulations 1997 (SI 1997/1904) modified Parts K (Protection from falling, collision and impact) and N (Glazing: safety in relation to impact, opening and cleaning). The crucial requirement is notification to the Local Authority of impending work covered by the Regulations. Generally, any alteration is required to conform with the current Building Regulations. For example, Building Regulations consent is required for any changes to full wall partitions as this affects the means of escape, (which requires consideration of lighting, signage etc). Some variations of the provisions set out may be allowable, for example, fire safety regulations for buildings of special architectural or historic interest. Regulation 6 requires that for a change of building use, the building must subsequently comply with Part A Structure. General Building Regulations approval will be required from the local planning authority. Application guidance is provided in Building regulation and fire safety: Procedural guidance [127]. Workplace Regulations (Health, Safety and Welfare) 1992 (SI 1992/3004) Made under the Health and Safety at Work etc Act These Regulations apply to all places of work with a few exceptions, notably means of transport and construction sites. There are requirements regarding working environment, safety, facilities and housekeeping which apply to both new and refurbished workplaces. 98 Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

111 APPENDIX A Responsibility for compliance rests with the employer. Specific parts of the UK Regulations deal with ventilation, temperature, lighting, escalators, sanitary conveniences, washing facilities and drinking water. Reference is made in the UK regulations to the CIBSE Guide as a deemed to satisfy document. The Healthy workplaces [128] booklet from CIBSE provides guidance on complying with the 1992 Health and Safety Regulations. Further guidance is provided in Workplace health, safety and welfare, Approved Code of Practice [129]. CDM Regulations - The Construction (Design and Management) Regulations 1994 (SI 1994/3140) transpose the European Community Temporary and Mobile Construction Sites Directive (92/57/EEC) into UK legislation. Guidance on their application is contained in the Approved Code of Practice [130] and CDM Regulations - case study guidance for designers [131]. The Regulations place duties on clients, planning supervisors, principal contractors, designers and contractors to plan, co-ordinate and manage health and safety at construction sites. It requires companies to consider health, safety and environmental aspects throughout the life cycle of a building and its plant, including site preparation, construction, commissioning, operation, maintenance and demolition stages. It requires designers to include adequate regard to the health and safety of persons affected by the construction or by cleaning work. Further, it requires provision of two documents, which include drawings and calculations: a health and safety plan to convey health and safety information to those involved in the construction, and a health and safety file which holds the relevant information for those involved following completion of the works, ie. those involved in operation, maintenance, repair or demolition. Examples of issues relating to building services include: safe location of and access to plant and services removal and disposal of existing plant/services (stripping out) removal of asbestos, lead, galvanised pipework/tanks, refrigerant, dirt, dust, other hazardous substances (survey required) maintaining integrity of fire compartmentation lifting requirements isolation of plant, equipment, power etc flushing and chemical cleaning maintenance procedures for services. Examples of issues relating to civil/structural aspects include: survey of building condition demolition structural stability presence of asbestos and/or other toxic materials working at high level safe location of and access to areas required to be cleaned and/or maintained use of temporary supports excavation BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 99

112 APPENDIX A effect of pile driving on adjacent buildings and disused mine workings ground contamination. Disability Discrimination Act 1995 The full text is available at The Act covers a number of provisions including: employment, provision of goods, facilities and services; the buying and renting of land or property, harassment and victimisation. The employment provisions of the Act currently apply to businesses with more than 20 employees. The Act may require employers to make reasonable adjustment to the workplace to make it appropriate for use by disabled persons, whether they are physically or mentally impaired. This includes any alterations necessary to overcome building related impediments or the assignment of people with disabilities to particular areas. Buildings that allow access to the general public may be contravening the Act where it is impossible or unreasonably difficult for the public to gain access. Where the premises are leased, and the occupying employer or service provider (lessee) would not normally be entitled to make an alteration to the premises, the lessee is still required to make the alteration under the Act, having first written to the lessor to obtain consent. The lessee would be seen as being in breach of the Act if a written application is not made. The lessor has 21 days in which to respond. The responsibilities of employers and the providers of services or entertainment to the general public are being phased in and buildings are expected to be fully compliant by 2005 although this date is not confirmed. The emphasis should be on a well thought out strategy developed over a number of years rather than immediate and extensive refurbishment. Compliance is obviously less costly if it is included as part of a refurbishment programme and could increase a building's marketability [2]. An action plan for access is the core of the Act and this defines five main elements: an access audit of the site and premises or plans of proposed development an assessment of the building's owner or occupiers' administrative and business procedures consultation with users and local access groups a schedule of works and timetable a review procedure. Public buildings such as museums, theatres etc, may be eligible for funding from the National Lottery where accessibility is to be incorporated into a general refurbishment programme. Structural Regulations The majority of structural requirements are covered under British and European Standards. 100 Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

113 APPENDIX A A1.3 BUILDING SERVICES RELATED LEGISLATION A1.3.1 Fire safety Existing fire safety legislation has been developed in piecemeal fashion with the result that it is covered by over 60 pieces of legislation [132]. For the lay person who has to comply with the legislation it can be bewildering. The original building construction and any alterations are covered by the Building Regulations, which are enforced by the building control authorities, whereas fire safety in occupied premises is primarily regulated by the Fire Precautions Act 1971, which is enforced by the fire authorities. Other legislation and Local Acts may also impose other requirements, particularly where hazardous substances or processes are involved. The main fire safety legislation is described below. The advice of the local Building Control Officer and the Fire Officer should always be sought. Offices, Shops and Railway Premises Act 1963 The Act is wide ranging and includes requirements for Fire Precautions. The Act provides for ensuring adequate means of escape for a stated number of people working in the premises and with regard to the number of people other than those who are employed to work at the premises who may reasonably be expected to be in the premises at that time. The Act also requires that the means for fighting fire (whether in the premises or affecting the means of escape) and the means of giving warning in case of fire to the occupants are specified. The Act requires that employees are familiar with the means of escape from the premises, the routine to be followed in case of fire and the use of any means of fighting fire. A fire certificate is required for the premises covered by the Act where: a) more than twenty people work in the premises at any one time; b) more than ten people work on any floor other than the ground floor; c) explosive or highly flammable materials are stored. The Act requires that where material extension to, or material structural alteration of the premises, to increase the number of people employed to work therein at any one time above that stated in the certificate, the occupier shall, before effect is begun to be given to the proposals, give to the appropriate authority notice of the proposals. Further, so long as a fire certificate is in force with respect to any premises, the appropriate authority may at any time cause the premises to be inspected for the purpose of ascertaining whether there has been a change of conditions by reason of which the existing means of escape in case of fire have become insufficient. Thus, it is generally expected that the appropriate authority (normally the Fire Officer) is informed of any changes made to the building. BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 101

114 APPENDIX A Fire Precautions Act The requirements are similar to those expected under the Offices, Shops and Railway Premises Act. The Fire Precautions Act covers premises where one of the following classes of use is carried out: a) use as, or for any purpose involving the provision of sleeping accommodation; b) use as, or as part of, an institution providing treatment or care; c) use for purposes of entertainment, recreation or instruction or for purposes of any club, society or association; d) use for purposes of teaching, training or research; e) use for any purpose involving access to the premises by members of the public, whether on payment or otherwise. The fire authority may cause any part of the building to be inspected to ascertain whether there has been a change of conditions covered by the fire certificate as described under the Offices, Shops and Railway Premises Act. Further, any proposed alterations including a material alteration in the internal arrangement of the premises or in the furniture or equipment with which the premises are provided shall be notified to the fire authority before carrying out any of the proposals. Fire Precautions (Workplace) Regulations 1997 (SI 1997/1840). (The full text is available at The Regulations are designed to give effect to parts of Council Directives 89/391/EEC and 89/654/EEC in so far as they relate to fire precautions. The Regulations require minimum fire safety standards in all places where people work, particularly those that do not have a Fire Certificate. The employer or anyone who is accountable for control of the workplace is responsible, although landlords have an obligation where they are responsible for building maintenance and safety. The main responsibilities relate to ensuring that all equipment relating to fire detection, annunciation, extinguishing and escape are kept in good working order and that staff are adequately trained. Future fire safety legislation The Home Office believes that it should consider an opportunity for a radical overhaul of existing fire safety law including rationalisation and the adoption of a modern approach which treats fire precaution measures in proportion to the risk faced. This is more in line with the approach of EC health and safety legislation as well as the Health and Safety at Work Act 1974 which is based on a general duty to provide safe working conditions. This is illustrated by the nature of the Fire Precautions (Workplace) Regulations 1997 detailed above which requires a general duty to provide and maintain adequate general fire precautions, compared to the prescriptive Fire Precautions Act 1971 which demands inspection of certain buildings by the fire authority before certification is issued. 102 Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

115 APPENDIX A The Home Office believes that there should only be one main piece of legislation covering general fire safety which would necessitate its removal, as far as is possible, from the Health and Safety at Work Act Further, the new Fire Precautions (Workplace) Regulations 1997 would be incorporated into any new Act thus rendering the 1997 Regulations redundant. Fire safety legislation for the future [132] and Fire in the pipeline [133] offer further information. A1.3.2 Lighting Workplace Regulations (Health, Safety and Welfare) 1992 (SI 1992/3004) The general scope of the regulations are described above. With regard to lighting the Regulations require that every workplace shall have suitable and sufficient lighting and that, so far as is reasonably practicable, the lighting shall be by natural light. The Approved Code of Practice [129] defines sufficient as to allow people to move safely and to operate without eyestrain. More specifically, there must be no shadows over stairs and local lighting must be provided at individual workstations and hazard points. Lights must be safely positioned, not obscured by stacked goods, and should be cleaned and serviced regularly. The absolute minimum levels of lighting level for the safe performance of a task are listed in the Health and Safety Executive's Lighting at work [134]. These minimum levels are not appropriate for long term performance of a task for which, reference should be made to CIBSE Code for Interior Lighting [29]. Display screen equipment (visual display units) Directive (90/270/EEC) is implemented by the Health and Safety at Work (Display Screen Equipment) Regulations 1992 and requires that workstation design must take into account environmental factors such as lighting and glare. The onus is on the employer to assess the risks of using display screen equipment. Guidance for employers is provided in Display Screen Equipment at Work: A Guide to the Regulations [135]. Emergency lighting The Workplace (Health, Safety and Welfare) Regulations 1992 (SI 1992/3004) requires that existing workplaces comply from 1996 with the requirements regarding working environment, safety, facilities and housekeeping. This includes the requirements for emergency lighting, namely that suitable and sufficient emergency lighting shall be provided in any room in circumstances in which persons at work are specially exposed to danger in the event of failure of artificial lighting. Minimum levels of illuminance from emergency lighting are set out in BS 5266 [136,137]. Further information is provided in CIBSE TM12: Emergency lighting [138]. Emergency lighting may also be required under local fire regulations. BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 103

116 APPENDIX A A1.3.3 Lifts The Lifts Regulations 1997 (SI 1997/831) (The full text is available at These Regulations implement the European Parliament and Council Directive 95/16/EC (OJ No. L213, of 7/9/95 - The Lifts Directive). The Regulations apply to all lifts and safety components placed on to the market or put into service after 1st July 1997 (but excluding until 30 June 1999 lifts and safety components complying with provisions in force on 29 June 1995) and primarily relate to ensuring that the lift or components satisfy the relevant health and safety requirements, are CE marked, and have been the subject of a conformity assessment procedure. A list of essential health and safety requirements is provided and includes adequate space and strength of the car, minimisation of risk of the car falling, control of loading levels and maximum speed, accessibility and safety of controls, safety of persons both inside and outside the car, and other hazards. Building services issues might relate to such items as: provision of controls for use by unaccompanied disabled people, requirement for sufficient ventilation even in the event of a prolonged stoppage, means of two-way communication, requirement for lifts to refuse new commands yet complete the movements in progress in the event that the lift machine room exceeds the maximum temperature set by the installer of the lift. Safety of existing lifts Immediately prior to adopting the Lifts Directive the Commission published an official recommendation (OJ L 134/37 of 20/6/96) concerning improvement of the safety of existing lifts. Because several member states have not enacted regulations on the safety of lifts, they are now urged to legislate to ensure a satisfactory level of maintenance and to improve the safety of existing lifts according to the following principles. Principles relating to improvement of the safety of existing lifts European standards EN81-1 and EN 81-2 (Safety rules for the construction and installation of lifts and service lifts: Part 1: Electric lifts and Part 2 Hydraulic lifts, may be applied, whenever possible, in order to obtain numerical values relating, in particular, to dimensions, tolerances, speeds or acceleration rates. 1) Car doors to be fitted and a floor-level indicator to be fitted inside the car. 2) The car suspension cables to be inspected and possibly replaced. 3) The stop controls to be modified in order to achieve a high degree of precision in the stopping level of the cart and a gradual deceleration. 4) Make the controls in both cars and lifts wells intelligible and usable by unaccompanied disabled persons. 5) Fit human or animal presence detectors to the automatic doors. 6) For lifts which travel faster than 0.6 m/s, fit a parachute system allowing them to decelerate smoothly when stopping. 7) Modify the alarm systems to establish a permanent link with a high-speed breakdown service. 8) Eliminate any asbestos in the braking systems, where this exists. 104 Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

117 APPENDIX A 9) Fit a device preventing uncontrolled movements towards the top of the car. 10)Provide cars with emergency lighting that operates in the event of a main power supply failure. It must operate long enough to enable the rescue services to intervene in the normal manner. The installation must also enable the alarm system provided in item 7 to function. A1.3.4 Ventilation The Workplace (Health, Safety and Welfare) Regulations 1992 state that: 1) There must be sufficient fresh air, having regard to the working methods used and the physical demands of the workers. 2) Forced ventilation systems must be maintained in working order. 3) Air conditioning or mechanical ventilation systems must operate so as not to expose workers to draughts which cause discomfort. 4) Any deposit or dirt likely to create danger to the health of workers by polluting the atmosphere must be removed without delay. Quantitative guidance is not specified in the UK Regulations or the accompanying Code of Practice, but the CISBE Guide and CIBSE design documents are quoted as deemed to satisfy. A1.3.5 Heating and air conditioning Table 16 The Efficiency Requirements Type of boiler Standard boilers Low temperature boilers* Gas condensing boilers The Boiler (Efficiency) Regulations 1993 (SI 1993/3083 amended by SI 1994/3083 which implement European Directives ECDIR 92/42 and ECDIR 93/88 respectively). These Regulations define efficiency requirements for new hot water boilers fired with liquid or gaseous fuels. All new boilers with output between 4 and 400 kw have to meet the following efficiency standards quoted at: a) rated output, that is, operating at rated output Pn expressed in kw, at an average boiler-water temperature of 70 C, and b) part load, that is operating at 30% output, at an average boilerwater temperature which varies according to the type of the boiler. Range of Efficiency at rated output Efficiency at part load power output kw Average boiler-water temperature expressed in C Efficiency requirement expressed in % Average boilerwater temperature expressed in o C Efficiency requirement expressed in % 4 to log Pn log Pn 4 to log Pn log Pn 4 to log Pn 30** log Pn * Including condensing boilers using liquid fuels. ** Temperature of boiler water Pn is rated output, expressed in kw. BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 105

118 APPENDIX A The Workplace (Health, Safety and Welfare) Regulations 1992 state that: 1) The temperature shall be reasonable 2) Heating and cooling methods shall not produce offensive fumes 3) A sufficient number of thermometers shall be provided to enable persons at work to determine the temperature in any workplace inside a building. Reasonable temperature is explained in the Approved Code of Practice as providing reasonable comfort without the need for special clothing. The temperature should normally be at least 16 C (dry bulb temperature at working height) or 13 C where strenuous effort is involved. Reference is made to CIBSE Guide Volume A for design data relevant to workplace temperatures. The Health and Safety (Display Screen Equipment) Regulations 1992 add that equipment belonging to any work station shall not produce excess heat which could cause discomfort to operators or users. Also that an adequate level of humidity shall be established and maintained. The CIBSE Guide Volume A recommends a humidity level of between 40% and 70% for most applications. Cooling systems Environmental protection (Controls on substances that deplete the ozone layer) Regulations (SI 1996/506). These regulations were made under the European Communities Act 1972 and the Environmental Protection Act They prohibit the import into the UK of substances that deplete the ozone layer and make it a personal and corporate offence to use these prohibited imports. These substances are set out in EU Council Regulation (3093/94). It should be noted that whilst production and import of CFCs (Chlorofluorocarbons) is banned it is currently still possible to recycle existing stocks, which has allowed operation of many CFC systems for longer than was anticipated. It is likely that the EU will take action against this. Further, some EU states are banning HCFCs (Hydrochlorofluorocarbons) ahead of EU regulation. It is possible that the EU will accelerate the HCFC (eg R22) phase-out in the light of this. BRE Information Paper IP6/98 [139] recommends that HCFCs should not be used in new systems and warns that there is likely to be a 10- year limit on being able to service existing plant. 106 Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

119 REFERENCES REFERENCES 1 Department of the Environment, Transport and the Regions, Construction Market Intelligence Division, web-site gov.uk/cmi/greenc/htm#orders, May THE CONNAUGHT REPORT. Refurbishment in the office sector 1997/8. The Royal Institution of Chartered Surveyors A guide to the management of building refurbishment. Report 133. London. Construction Industry Research and Information Association (CIRIA) pp 80. ISBN GOLD CA AND MARTIN AJ. Refurbishment of concrete buildings: The decision to refurbish. Guidance Note GN 7/99. BSRIA ISBN BS 6399, Loading for buildings: Part 1, Code of practice for dead and imposed load, London, British Standards Institution ISBN Workplace (Health, Safety and Welfare) Regulations SI 1992/3004. HMSO GOLD CA AND MARTIN AJ. Refurbishment of concrete buildings: Designing now for future re-use. Guidance Note GN 9/99. BSRIA ISBN KENDRICK C, MARTIN A J AND BOOTH W B. Refurbishment of air-conditioned buildings for natural ventilation. Technical Note TN8/98. September ISBN All at '60s and '70s. Building Services and Environmental Engineer. December P An introduction to serviced offices. Facilities Management Guide. May pp MELBOURNE C. Honorary editor. Proceedings of the Institution of Civil Engineers. Historic concrete structures and buildings. August/November 1996, Thomas Telford, London. ISSN pp STANLEY CC, Highlights in the history of concrete, Slough, Cement and Concrete Association, pp 44, ISBN X. 13 ANON. The use of prestressed concrete in buildings, London, Percy Lund, Humphries & Co. Ltd 1964, pp 16. ISBN X STEVENSON AM, Post-tensioned concrete floors in multi-storey buildings, Crowthorne, British Cement Association (on behalf of the Reinforced Concrete Council), pp 20, ISBN ELLIOTT KS, Multi-storey precast concrete framed structures, Oxford, Blackwell Science Ltd, pp 601, ISBN DIAMANT RME, Industrialised buildings 3, 70 international methods, third series, London, Iliffe Books Ltd pp216, ISBN DEESON AFL, The comprehensive industrialised building systems annual 1970, West Wickham, Kent, Morgan-Grampian (Publishers) Ltd, pp 351, C.P. 116:1965 The structural use of precast cement. Ministry of Public Building and Works BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 107

120 REFERENCES 19 CREASY LR, The public building frame, London, Cement and Concrete Association, pp 37, Rethinking Construction -The Report of the Construction Task Force. DETR. July Owning, operation and maintenance of building services. CIBSE Technical Memorandum. In preparation. 22 BS 5839 (Parts 1 to 8): Fire detection and alarm systems for buildings. 23 BS 5445 (Part 1 to 11): Components of automatic fire detection systems (some parts are equivalent to EN54). 24 BS EN54 (Part 1 to 9) Fire detection and fire alarm systems. 25 BS 7807: Code of practice for: Design, installation and servicing of integrated systems incorporating fire detection and alarm system and/or other security systems for buildings other than dwellings ISBN BS 7671:1992. Requirements for electrical installations: IEE Wiring Regulations 16th Edition ISBN PEARSON C. The designers' guide to power quality problems. Building Services Journal. February pp Electrical design - a good practice guide. CDA Publication 123. Copper Development Association. December CIBSE Code for interior lighting. CIBSE ISBN Daylighting in buildings. Thermie maxibrochure. Organisationfor the Promotion of Energy Technologies (OPET) Energy management and good lighting practices. Fuel Efficiency Booklet 12. EEO BUILDING REGULATIONS: Part L. Conservation of Fuel and Power. HMSO Heating system option appraisal - an engineer's guide for existing buildings. Good Practice Guide 187. Department of the Environment, Transport and the Regions BRITTAIN J R J. Oversized heating plant. Guidance Note GN12/97. BSRIA ISBN BRITTAIN J R J. Oversized air handling plant. Guidance Note GN11/97. BSRIA ISBN BS 4434: 1995 and BS EN 378. Specification for safety and environmental aspects in the design, construction and installation of refrigeration appliances and systems. HMSO ISBN LICKLEY J M. Giving a lift a lift. Building Services. September pp BS EN115. Safety rules for the construction and installation of escalators and passenger conveyors. HMSO ISBN Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

121 REFERENCES 39 LOYD S. Ventilation system hygiene - a review. Technical Note TN 18/92. BSRIA ISBN X. 40 Structural renovation of traditional buildings. CIRIA. Report Appraisal of existing structures, (Second Edition), London Institution of Structural Engineers pp 106. ISBN X. 42 Structural appraisal of existing buildings for change of use. Digest 366. BRE ISBN JACK AG AND VENESS KJ. The assessment of existing foundations using NDT. Construction Repair. Vol. 10. No.5, September/October pp ISSN Guide to surface treatments for protection and enhancement of concrete. Technical Report No. 50. The Concrete Society pp 87. ISBN Structural effects of alkaline-silicon reaction. Technical guidance on the structural appraisal of existing structures. Institution of Structural Engineers pp 45. ISBN BATE S, High alumina cement concrete in existing building superstructures. Report 235. HMSO. BRE ISBN Assessment of existing high alumina cement construction. Digest 392. Building Research Establishment ISBN SPRINGINGS I, Princess House, Swansea. Construction Repair, Vol. 10, No. 4 July/August pp 8 and 9. ISSN MONKS W, Appearance matters 3 - The control of blemishes in concrete, Slough, Cement and Concrete Association pp 20. ISBN Non-structural cracks in concrete. Technical Report No. 22. Third Edition. The Concrete Society pp 48. ISBN Report of the Joint Committee on Reinforced Concrete. Journal of the Royal Institute of British Architects. 3rd series, 14. No SOMERVILLE G. Cement and concrete as materials: changes in properties, production and performance. Proceedings of the Institution of Civil Engineers, Structures and Buildings. Vol Nos. 3&4. August/November pp ISSN BS Structural use of concrete: Part 1, Design, materials and workmanship: Part 2, code of practice for special circumstance. London. British Standards Institution. ISBN AUSTIN JA. Over-design: fact or fiction? The Structural Engineer. Volume 76/Number ISSN BARNARD N. Dynamic energy storage in the building fabric. TR9/ BSRIA. ISBN MEIERHANS RA. Slab cooling and earth coupling. ASHRAE Transactions. 99. Part pp BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 109

122 REFERENCES 57 Space for services. 7. Distribution within spaces. Architects' Journal. 26 March pp WINWOOD R, BENSTEAD R AND EDWARDS R. Advanced fabric energy storage 1: Review. Building Serv. Eng. Res. Technol. (BSERT). CIBSE. 18 (1). pp Selecting air-conditioning systems. A guide for building clients and their advisers. Good practice Guide 71. Department of the Environment, Transport and the Regions Space for services. 5. Distribution and sizing. Architects' Journal. 5 March pp CLARKE I. Sounding out the soffit. Architects' Journal. 7 March pp Kimberlin Library Extension, De Montfort University. Building Services Journal. October p Air conditioning and displacement ventilation model. Building Services Journal. September p PAVEY N. Rules of Thumb. Technical Note TN17/95. BSRIA ISBN Space for Services. 6. Structure and services. Part 2 Integration. Architects' Journal. 19 March pp SPRING M. New flesh on old bones: Reconstructing 1960s office blocks. Building. 1 September pp CIBSE. Window design. Applications manual AM2. CIBSE ISBN CIBSE. Natural ventilation in non-domestic buildings. Applications manual AM10. CIBSE ISBN Selecting energy-efficient windows. Good practice guide 227. DETR PERERA M D A E S, TURNER C H C AND SCIVYER C R. Minimising air infiltration in buildings. BRE Report BR ISBN POTTER I N. Air tightness specification. Specification 10/98. BSRIA ISBN SUNPIPE TRADE LITERATURE. Monodraught Ltd, High Wycombe, Bucks. 73 BAKER N V. Energy and environment in non-domestic buildings. Cambridge Architectural Research. 74 WINDCATCHER TRADE LITERATURE. Monodraught Ltd, High Wycombe, Bucks. 75 BRECSU. Avoiding or minimising the use of air conditioning. Best Practice Programme Report 31. HMSO KING G R AND SMITH M H. VRF based air conditioning systems - performance, installation and operation notes. Technical Note TN 10/97. BSRIA ISBN Energy efficient lighting in buildings. Thermie maxibrochure. Organisation for the Promotion of Energy Technologies (OPET) Available from BRECSU. 110 Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

123 REFERENCES 78 ENV , General principles for the use of products and systems for the protection and repair for concrete structures. Definitions, requirements, quality control and evaluation of conformity. London, British Standards Institution Pp 42. ISBN Non-structural cracks in concrete. Technical Report No. 22. Third Edition. The Concrete Society pp 48. ISBN Cathodic protection of reinforced concrete. Technical Report No. 36. The Concrete Society pp 73 ISBN Model specification for cathodic protection of reinforced concrete. Technical Report No. 37. The Concrete Society pp51. ISBN PERKINS P H. Repair, protection and waterproofing of concrete structures. Third edition, London. E & FN Spon, ISBN Assessment and repair of fire-damaged concrete structures. Technical Report No. 33. The Concrete Society pp 77. ISBN PROVENGHI, SG AND BRANDOW GE. Evaluation, repair and reinforcement of a vetra-thin two-way flat slab with drop panels. Volume 2: Evaluation and Rehabilitation of Concrete Structures and Innovations in Design. ACI SP pp ISBN SUN BJ. Rehabilitation of a grillage floor building. The Structural Engineer. Vol. 76, No. 2, January pp ISSN CAIRNS J AND RAFEEQI SFA. Behaviour of reinforced concrete beams strengthened by external unbonded reinforcement. Structural Faults and Repair 95. London. Vol pp ISBN LENKEI, P Assessment and upgrading of concrete structures in an existing building - a case study. In: Re-evaluation of Concrete Structures. Copenhagen. Danish Concrete Institute, pp MIDWINTER K R. Plate bonding carbon fibre and steel plates. Construction Repair. January- February pp 5-8. ISSN HUTCHINSON A R AND RAHIMI H. Flexural strengthening of concrete beams with externally bonded FRP reinforcement. In: El-Badry MM, Advanced Composite Materials in Bridges and Structures. Montreal. Canadian Society for Civil Engineering pp ISBN TAERWE L. Non-metallic (FRP) for concrete structures. London. E & FN Spon pp 715. ISBN CHAALLAL O, NOLLET M-J AND PERRATON D. Strengthening of reinforced concrete beams with externally bonded fiber-reinforced-plastic plates: design guidelines for shear and flexure. Canadian Journal of Civil Engineering. Vol. 25. No. 4. August. pp National Research Council of Canada, Ottawa ISSN STEINER W. Strengthening of structures with FRP strips. In: El-Badry MM. Advanced composite materials in bridges and structures. Montreal. Canadian Society for Civil Engineering pp ISBN BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 111

124 REFERENCES 93 PARKER D. Sticking to the task. New Civil Engineer. 11 July, ISSN GOODCHILD C. Economic concrete frame element. Crowthorne. British Cement Association (on behalf of the Reinforced Concrete Council). pp 128. ISBN SUBEDI K AND BAGLIN PS. External plate reinforcement for strengthening concrete beams. Construction Repair. Vol. 10, No. 6 November/December pp ISSN NORRIS T. Saadatmanesh H and Ehsani M R. Shear and flexural strengthening of RC beams with carbon fibre sheets. Journal of Structural Engineering. American Society of Civil Engineers. July pp ISSN MAYS G AND CALDER A. External plates extend reinforcement s reach. Concrete. November pp ISSN GODFREY J AND SHARKEY P. Plate bonding to strengthen hall floor. Construction Repair. Vol. 10, No. 4. July/August pp ISSN FRANGOU M, PILAKOUTAS K AND DRITSOS S. Structural repair/strengthening of RC columns. Construction and Building Materials. Vol 9, No pp ISSN WINFIELD PF AND HARVEY SJ. Vantage west the refurbishment of a 1960s office block. The Structural Engineer. Vol. 69, No. 9. May Pp ISSN LILLISTONE D AND JOLLY CK. Concrete-filled fibre reinforced plastic circular columns. Composite Construction - Conventional and Innovative. IABSE, Innsbruck, Austria pp ISBN DRITSOS SE. Jacket retrofitting of reinforced concrete column. Construction Repair. Vol. 11, No. 6. July/August pp ISSN KLIGER H. Repair of parking structures. FRP International. Vol. IV, Issue 4. Autumn, pp EHSANI MR. Strengthening of earthquake-damaged masonry structures with composite materials. In: Taerwe L, Non-metallic (FRP) reinforcement of concrete structures, London, E & F N Spon pp ISBN WHITEHEAD T. The bank job. Contract Journal. Vol No May 9, ISSN BHATTI MA, LIN B AND IDELIN MOLINAS VEGA JP. Effect of openings on deflections and strength of reinforced concrete slabs. Recent developments in deflection evaluation of concrete, American Concrete Institute pp Library of Congress no LINDSELL P. Don't let tension be a worry. National Federation of Demolition Contractors Yearbook pp 60, 62 and Standard reinforced concrete details, Report of the Working Party. London. The Concrete Society pp 28. ISBN BS Code of practice for demolition. London. British Standards Institution ISBN Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99

125 REFERENCES 110 FELSTEAD AE AND LINDSELL P. Controlled demolition of a post-tensioned beam. Concrete. Vol. 15. No. 9. September pp ISSN ROBERT J M. Demolition of Marks & Spencer, Manchester (a six- storey commercial building supported by post-tensioned beams). The Structural Engineer. Volume 77 Number ISSN HAWES F. Appearance matters 6, The weathering of concrete buildings. Slough. Cement and Concrete Association pp 48. ISBN Patch repair of reinforced concrete - subject to reinforcement corrosion. Technical Report No. 38. The Concrete Society pp 87. ISBN GRAVES P. Tackling a high rise refurbishment problem. Clerk of Works. May p HARRISON G. Long life coatings combat the high rise refurbishment problem. International Journal of Construction Maintenance and Repair. Vol.5, No.2. March/April ISSN WARN J. UK's largest concrete refurbishment completed. Construction Repair. Vol 8, No 5. September/October p 28. ISSN HINKS J AND COOK G. Refurbishment options for damp basements. Architect and Surveyor. Vol. 66, No. 10. November pp 17, 18 and 20. ISSN Water-resisting basements. Report 139. London. Construction Industry Research and Information Association pp 189. ISBN Water-resisting basements (Summary report). Report 140. London. Construction Industry Research and Information Association pp 62. ISBN FITZGERALD TD. Failure and rectification of fixings of large precast concrete cladding units. Structural faults and repair '87. Proceedings of the international conference on structural faults and repair. Vol pp ISBN Factory with a facelift. Architects' Journal. 3 November, SHAW R, LOVELL M AND COOK M. No. 1 Neathouse Place. Concrete Engineering International. March pp3-7. ISSN WELLS M. Neat and tidy. RIBA Journal. February pp ISSN JOHANSSON M. Building Services Legislation. 4th Edition. Directory D4/98. BSRIA ISBN GREGORY D AND KING A. The practical guide to EC rules for building services products. BSRIA ISBN SPEARHEAD - Online database of existing and forthcoming European Commission Legislation. DTI Tel for further information. 127 Building regulation and fire safety: Procedural guidance. Department of the Environment. June BCA/BSRIA GN 8/99 Refurbishment of Concrete Buildings: Structural & Services Options 113

126 REFERENCES 128 Healthy workplaces. Guidance Note GN2. CIBSE ISBN Workplace health, safety and welfare. Approved Code of Practice. L24. HSE Managing construction for health and safety: Construction (Design and Management) Regulations Approved Code of Practice. L54. HSE CDM Regulations - case study guidance for designers: An interim report. Report 145. CIRIA ISBN Fire safety legislation for the future. Building Control. February pp EVANS B Fire in the pipeline. Architects' Journal. 7 May p Lighting at work. HS(G) 38. HSE. 135 Display screen equipment at work: A guide to the regulations. L26. HSE BS Part 1: Code of practice for the emergency lighting of premises other than cinemas and certain other specified premises used for entertainment ISBN BS Part 2 Code of practice for electrical low mounted way guidance systems for emergency use ISBN CIBSE. Emergency lighting. Technical Memoranda TM12. CIBSE Performance of air-conditioning systems with alternative refrigerants. Information paper IP6/98. BRE Refurbishment of Concrete Buildings: Structural & Services Options BCA/BSRIA GN 8/99