Basements for housing

Transcription

1 Benefits and solutions for sustainable housing

2 Contents Types of basements 4 Benefits of basements 6 Optimising development potential 9 Construction techniques 11 Design issues 15 Costs 19 Building legislation 20 Appendix and further reading 22 Introduction This document considers the role of basements as a viable part of the solution to sustainable housing in the UK, through consideration of their specific attributes in relation to planning policy and the Code for Sustainable Homes. Outlining the key issues to be considered at each stage of the design and construction process for single-storey basements in domestic housing, guidance is additionally offered on sources of more detailed advice. The Code of Practice for protection of below-ground structures against water from the ground (BS 8102) was revised and re-issued in December About this publication Domestic basements can aid in the creation of desirable, sustainable homes, providing greater flexibility and adaptability of space; thus extending the design life of the building. Including a basement maximises usage of available land, provides a stable construction base and improves thermal efficiency. Modern basements offer the possibility of additional, alternative living spaces in dry, warm, day-lit rooms with good ceiling heights and ventilation levels. Usage potential ranges from ideal quiet areas for home working or leisure to additional space for storage and parking. The use of full or partial basements in housing can play a significant role in meeting current and future needs for new homes in the UK. Basement design supports basic sustainability principles such as longevity, durability and adaptability, as well as providing useful space for many of the additional requirements needed to comply with the Code for Sustainable Homes. Definition: Basement Throughout the document, the term basement refers to a usable part of a building that is situated partly or entirely below ground level, as defined by the British Standards Institute [1]. Building regulations in England and Wales define a basement storey as at least 1.2m below adjoining ground level [2]. Occasional reference is made in this document to partial- or semibasements to remind readers that usable domestic basements are likely to include windows and doors for natural lighting and ventilation. All walls enclosing a basement may not, therefore, be fully below ground level; for example on sloping sites or with lowered courtyards. This document is principally concerned with the issues associated with new basement construction rather than existing cellars since the latter is, by definition, limited to space for storage below ground with less requirement for daylighting and ventilation. Much of the guidance is, however, relevant to the conversion of old cellars into habitable basements. An example of a new build development with a basement. 2

3 The case for basements today Changing requirements for housing Houses with below-ground space used to be common in the UK but their construction has declined over the last century. In mainland Europe and North America, however, basements have continued to be incorporated into new dwellings. In Germany, they are included in almost 98% of housing stock. The decline in the UK was due, in part, to changes in living requirements. Improved transport, convenience food and the use of electric fridges diminished the need for naturally cool areas to store food and, together with changes in social attitude, the need for a space below stairs for domestic help. Until recently, reliance on cheap gas and electricity also reduced the need for areas in the home to store fuel. However, housing in the UK is currently undergoing a radical reevaluation of its design and performance, as a result of evolving legislation and attitudes towards sustainability and energy efficiency. Established construction techniques and space-planning solutions for housing are being challenged and tested against a new set of sustainable performance criteria, and basements are once more considered relevant and attractive additions to housing. In addition to the drive for low energy housing, there is a movement towards increasing the size of new housing, in response to reports by various organisations, including the Commission for Architecture and the Built Environment (CABE), Homes and Communities Agency and Mayor of London Office. The provision of homes that have sufficient space to develop and grow with the requirements of a family is a significant sustainability issue for housing. The sustainability benefits of basements are described in the benefits of basements section of this document, and a summary of scoring credits applying to basements under the Code for Sustainable Homes is given in the Appendix. In Germany, and much of continental Europe, the basement provides the solution to the problem. Over there, asking for a house without a basement is like asking for a car without wheels. Government targets for housing and limited land availability A combination of Government targets for new housing and limited availability of land for new construction have led to greater consideration of increased densities and the development of difficult plots of land, such as sloping sites or those with poor soil stability. Planning Policy Statement 3: Housing (PPS3), underpinning delivery of the Government s strategic housing policy objectives, encourages increased density of housing developments. In addition, high land prices mean housebuilders are under increasing pressure to maximise potential returns through efficient use of land. The use of full or semi-basements can be a cost effective means of increasing the density of housing developments, without reducing amenity levels; particularly if planning requirements restrict the building footprint or height. Strategies for optimising residential development are explored on page 9 and 10 of this document. Improved construction techniques and contractor warranties The reliability and design of construction and waterproofing techniques has significantly improved over the years; backed by many successful examples both in the UK and abroad. Advice regarding the detail, design and construction of basements is well documented and available from The Basement Information Centre (TBIC), The Concrete Centre and National House-Building Council (NHBC), amongst others. NHBC arrangements with builders and developers provide cover under their standard building assurance system for the construction of basements [3]. Accreditation and indemnity schemes exist for specialist basement contractors. Details of accredited contractors (construction and waterproofing) may be found on The Basement Information Centre website. In addition, various manufacturers of specialist water-resisting concrete offer guarantees. An accreditation and insurance scheme, administered by the Association of Underpinning Contractors (ASUC), is available for underpinning of existing structures; most commonly required for refurbishment or retrofit basements. The correct procedures for design, soil investigation and construction are key to achieving robust and reliable basement construction. The various methods of construction on offer, and design issues, are summarised in the construction techniques and design issues sections of this document. Chris Drury - Weber House, Germany, commenting on the lack of storage space in UK housing. 3

4 Types of basements Basements can be broadly sub-divided into five categories, depending upon their location, time of construction relative to the main property and depth. A brief summary of the differences, and the key issues related to each, is outlined below. Table 1: Types of basements. Type of basement Description Details Benefits Other comments Refurbishment Alterations to existing space below ground. May require lowering the floor to increase head room; underpinning adjacent walls; improving ventilation and lighting. Typically involves improvements to, or new, waterproofing system; and new finishes and fixtures. Adds value and desirability of property Additional usable space Addresses potential existing damp problems Provides opportunities for new activities in property e.g. games room/gym/storage Building regulations approval will be required for any works. Planning permission may be required, depending on extent of works and intended use. * New garden basement New basement adjacent to existing property, usually in garden space. New structure below ground, with planted green roof or terrace at garden level. Access from main house via new external covered staircase. Adds value and desirability of property Additional usable space Provides opportunities for new activities in property Potential for natural daylight and ventilation through roof lights Planning and building regulations approval required. Likelihood of need for structural support to existing house is reduced as distance from house increases. New basement under new housing Basement space built as part of a new build development. Arrangement of windows and internal and external access vary. Designed to suit current and future use requirements, site conditions, cost and constructability. Adds value and desirability of property Future adaptability Usable space for sustainable technologies and recycling Potentially reduces footprint of house Increases thermal performance No additional building or planning regulation requirements provided it is included in initial application.* Retrofit New space created through excavation below ground floor of an existing property. Allows creation of additional space below business or homes, which benefit from staying in same location. Preservation of existing building possible (e.g. listed building) Underpinning works required. Adds value to property Additional space for business to develop in same location or family to expand Releases potential of empty property Planning and building regulations approval required. Specialist work. Generally only economically viable for high land value properties. Deep basements Spaces below one storey deep. Frequently used for car parking, plant/services space and storage below larger residential development and other uses including commercial, retail or mixed use schemes in urban areas. Building footprint and development potential optimised above ground Parking and space for deliveries possible Refer to Design and Construction of Concrete Basements [10]. * At time of writing works may not be allowable under Permitted Development Rights, depending on individual Local Authority. This may be revised in the near future. The situation should be confirmed with the Local Authority Planning Department. Note: The Party Wall Act could apply to each type of basement. See page 21. 4

5 Some examples of basement arrangements Figure 1: Basement garage and storage. External access via the driveway. Figure 2: Basement with gym, shower and sauna. External and internal access with light well for daylight and additional ventilation. Figure 3: Basement with games room, wine cellar and storage. With external courtyard for daylight and additional ventilation. Access via courtyard and separate internal stair. Figure 4: Basement with additional bedroom or annex to the property (granny flat or similar) with internal and external access.extra light provided via conservatory. Figure 5: Split level design with separate external access and light well. Potential for office or workshop. Figure 6: Garden basement with internal access and roof light above. 5

6 Benefits of Basements There are many reasons for the provision of basements in a housing development including: added value; increased development potential; occupant or purchaser attraction and sustainability. This section explains the key benefits. Desirable and adaptable spaces There is an evident desire for the provision of basements as part of our housing solution in the UK, illustrated by the significant number of basements constructed in the self-build market. In addition, studies by the Traditional Housing Bureau [4] indicate significant demand from home owners for more space. In the 2005 CABE report What home buyers want: Attitudes and decision making among consumers, basements are cited as particularly valuable in this regard. One of the major benefits of basements is allowing the creation of a single large space. Due to economies and method of construction, the floor above the basement level can be created in a single span, providing flexibility in the location of internal walls and allowing simple future alterations. Pre-subdivision, the resultant space is typically the single largest area in the house and, due to its location on a different level from the rest of the house, provides opportunity for uses not always possible to accommodate in more basic dwellings. In North America, Canada and continental Europe, it is common for basements to serve as multipurpose areas, for example games or utility rooms or storage areas. Basements can provide comfortable day-lit rooms, with natural ventilation and external access, as an extension to the living spaces above. They also provide the opportunity for more unique uses, such as gyms, music rooms and swimming pools. Alternatively, basements can simply provide practical space for games or hobby rooms, home offices parking or storage. Good sound insulation Good acoustic attenuation is provided by the concrete walls surrounding basement rooms by the earth itself and the ground floor if it is built from concrete. Basement spaces are therefore inherently well insulated for sound and ideal for locating noisy activities such as music practice, home cinemas or other loud equipment that could disturb neighbours or the rest of the house. Conversely, the quiet nature of the space provides a peaceful place for reading, relaxing or working; away from ground-level noise, in and outside of the house. Martin Grant Homes - Riverview Court development. Developers in the UK are now looking at basements as a solution for creating spacious homes whilst using the land available efficiently. Riverview Court development was built on a former water treatment works on a flat site, beside the River Cam, Cambridgeshire. 35 homes were built with sunken patios which provide natural daylight and ventilation to the basement kitchen and dining room. 6

7 Added value and space The provision of additional floor space in a home clearly increases the value of a property and the addition of a basement adds space with little or no effect on the garden area. The costs associated with constructing a basement are explored in the Costs section of this document. Sustainability benefits Including a basement in the design of domestic properties helps developers to address many of the fundamental principles of sustainable design, including improved energy efficiency, longevity and adaptability and support of local employment. Energy efficiency Basements benefit from the surrounding ground improving their energy efficiency. As a consequence, the amount of insulation needed to reduce heat loss through a basement wall is less than that required on upper floor levels [5]. The simple construction methods and minimum wall penetrations, associated with basement construction, also lead to minimal heat loss through cold bridging. Studies by TBIC and Building Research Establishment (BRE) highlight a potential 10 per cent saving in space heating for a two-storey house with a full ground basement compared with its threestorey equivalent above ground (both having the same amount of added insulation). The potential space heating saving rises to around 14 per cent for a single storey property with full basement, compared to its two-storey equivalent above ground [6]. Thermal mass The heavyweight nature of basement construction can be utilised to naturally regulate the internal temperature of a home and can be part of an energy efficient strategy for controlling the temperature of the whole house. The Met Office has projected average daily temperature rises throughout the UK, indicating the increasing need for low energy solutions to cool homes, which heavyweight construction - including basements - is well placed to provide. For further information refer to The Concrete Centre publications Thermal Mass Explained and Thermal Mass for Housing. The thermal mass properties of concrete are optimised by omitting insulating internal surface finishes. If insulated and waterproofed externally, basement concrete walls will offer greater thermal mass. This could be achieved with a fair-faced or painted finish, or alternatively a wet plaster finish. Fair-faced concrete offers potential cost and programming benefits, by omitting subsequent use of finishing materials and trades and associated waste produced on site. Air tightness and mechanical ventilation The construction of sustainable dwellings using low air permeability and mechanical ventilation with heat recovery, such as the Passiv Haus technique, is a means of improving the energy efficiency of the building fabric of dwellings. This is simply provided by basements, since the structure below ground is inherently more air tight. The addition of a basement increases the living space in a property, without compromising the garden. Courtesy of The London Basement Company. 7

8 Basements and the Code for Sustainable Homes Since 2008, all new homes require rating under The Code for Sustainable Homes (CSH) as part of Home Improvement Packs (HIPs). The inclusion of a full or partial basement can provide additional credits under the assessment criteria of the Code; for example, storage of waste, recycling, alternative fuel supplies such as wood pellets, other equipment associated with renewable energy or water recycling and even bikes. In addition, basements can be used to reduce the overall size of the building footprint, relative to the number of storeys, scoring points in the Ecology Section of the Code. A full list of how basements can assist with obtaining credits for Code for Sustainable Homes is found in the appendix of this document. Space for working from home Basements offer the possibility of quiet, private spaces for working from home, with the potential for direct access from the outside, and therefore designated work-based visits or deliveries. The solid nature of basement construction provides excellent conditions for workshop spaces and activities that create noise, require support for heavy equipment or require robust, cleanable surfaces. Changing uses for basement spaces during the life of a family home Extra storage (recycling/chest freezers) DIY work shop Utility room Hobby room Home Gym/Sauna Wet room outdoor gear All weather play room Band practice/music room Teenage den/bedsit Home office/studio Wine cellar Home cinema Granny annex Living room Basements provide flexible multipurpose spaces through the lifetime of a home. Courtesy of The London Basement Company. 8

9 Optimising development potential Higher density development - minimal extra height The use of a basement provides increased floor area in a development without significantly increasing the apparent size of the building; thereby improving the viability of a development, particularly in areas where building height or size of footprint is restricted. The potential to increase the number of proposed dwellings in one property is boosted if both a basement and habitable roof space are proposed; thereby potentially creating two additional storeys in a similar building envelope. Maximise site layout - build up to street boundary Utilise existing slope Partial basements on sloping sites become viable compared to alternative substructure construction options to make up ground levels. By lifting the ground floor level above street level to create upper and lower ground floors, properties can be constructed close to site boundaries while maintaining privacy for occupants. Consideration of Building Regulation Part M requirements for access are required. 9

10 Protect amenity space The use of a fully below-ground basement or partially below-ground basement gives increased usable space within the building footprint. Larger dwellings can therefore be built on small sites without losing amenity space around the buildings. Better use of poor sites with poor soil Where poor ground conditions necessitate deep foundations, the additional cost can be mitigated by including a basement to add space and therefore value to the proposed new properties. Where large areas of contaminated soil are removed from site, the viability of including a basement level is increased. If constructed before original ground levels are reinstated, the amount of replacement ground material is reduced and further excavation is unlikely. Back fill will need to be compacted around the walls, but in general the programme of construction is likely to benefit from improved access conditions. Stable building stock Basements create a good stable structural base, capable of supporting heavy loads above. By combining foundation design with the provision of habitable space, the extra depth of structure provides the building with greater ability to cope with climate change effects in the soil, such as shrinkage or tree roots. This means buildings with basements are less prone to movement and cracking as a result of potential future changes in soil conditions. Shading indicates equivalent accommodation areas located beside or below a dwelling, impacting on available garden space. Increased number of plots per hectare By incorporating facilities such as garages, utility rooms or habitable space at basement level, it is possible to reduce the footprint of a proposed property; thereby increasing the number of houses on a given site or along a fixed street frontage. Housing using a basement garage requires less street frontage, compared to houses with garages located alongside at ground level. 7.6m 6.0m 7.8m 9.0m 10.0m 9.0m 7.8m 6.0m 9 plots possible with basement garages, compared to 8 plots on the same site. 10

11 Basement construction Water resistant reinforced concrete wall and slab External waterproofing Sandwiched waterproofing Internal waterproofing Type A: External barrier or internal protection Water-resistent reinforced concrete or blockwork with waterproofing located either externally, internally waterstop as required reinforced concrete wall External Sandwiched Internal or sandwiched. and slab waterproofing A non-integral kicker should be avoided as it will require one waterstop where it adjoins the slab and another at the intersection with the wall waterproofing Waterstop required at junction between wall waterproofing and slab and at all construction joints. e.g Crystallisation, hydrophilic or injected waterstop Types of waterproofing protection There are three main methods of providing protection against ground water for residential basements. These are defined in BS 8102 as types A, B and C. Their application is influenced by the ground conditions and proposed building use. The definition of terms and guidance related to their appropriate usage, are highlighted in the 2009 revision. Alternative approaches The traditional method of waterproofing domestic basements in Britain was a single barrier method (Type A) or drained protection (Type C). Earlier materials used in basement construction have since been developed into more durable waterproofing membranes. External or internal Water-resistent Slab with integral waterstop kicker as required Slab with kickerless construction External reinforced Sandwiched Waterstop Internal required waterproofing concrete waterproofing wall at junction waterproofing between A non-integral kicker and slab wall and slab and at Water resistant should be avoided as it all construction joints. reinforced Drained cavity concrete wall will require one waterstop where it adjoins the Internal block e.g Crystallisation, wall hydrophilic or and slab Inner skin slab and another at the Wall cavity intersection with the wall Concrete/steel piled wall injected Access waterstop point(s) to drainage External or internal Drainage channel Water-resistent waterstop as required Waterstop at junction reinforced Waterstop required Slab with integral kicker to follow wall profile concrete Slab with wall kickerless construction at junction between A non-integral kicker and slab wall and slab and at Water resistant Sump should formed be avoided in situ as it all construction joints. reinforced Type B: structural or will separate integral require drain one waterstop where may be it adjoins solid the Internal block hydrophilic wall or protection - reinforced or e.g Crystallisation, concrete Drained wall cavity which and prestressed slab concrete or perforated designed through Floor composite slab with integral slab and another at the and injected waterstop protection and/or added May incorporate integrated details, intersection Pump such as with water the Wall wall bars, cavity to membrane be water (internal resistant. Access or drainage channel Inner skin external) point(s) to with pipe connection Concrete/steel piled wall drainage to setup Drainage channel Slab with integral kicker Slab with kickerless construction Waterstop at junction to follow wall profile Drained cavity Sump formed in situ or separate drain which may be solid Internal block wall or perforated Floor slab with integral Wall cavity protection and/or added Access May incorporate Inner skin Pump membrane (internal or point(s) to drainage channel Concrete/steel piled wall external) drainage with pipe connection to setup Drainage channel May incorporate drainage channel with pipe connection to setup Pump Waterstop at junction to follow wall profile Sump formed in situ or separate drain which may be solid or perforated Floor slab with integral protection and/or added membrane (internal or external) Further alternative approaches have been developed, whereby hydrostatic pressure on the wall structure is eliminated. These methods incorporate a drainage blanket around the perimeter of the basement, allied to effective drainage below the floor slab and around the building. Suitability depends on the drainage characteristics of the ground and topography. A combination of systems can also be an appropriate design solution. For example, the application of additional waterproofing systems to a Type B structure will improve water vapour control or provide further protection against water ingress. Each of these methods is viable for domestic basements in Britain, depending upon the specifier s preference, site conditions, the type of development and perceived risk. Table 2 on page 12 provides a summary of appropriate waterproofing protection for varying risks associated with water table levels and useful additional measures to reduce risk dependant on project particulars [7]. BS 8102 should be consulted for further details. Type C: drained protection any water seeping through external walls and floor is drained to a sump via an internal cavity, typically created by a proprietary cavity system and pumped or drained away. Diagrams from The Design Guide, courtesy of TBIC, Double height concrete basement extension to existing property. Courtesy of ph+ architects. 11

12 Table 2: Types of waterproofing protection Risk associated with water table Water table classification* Waterproofing protection Type A Type B Type C Piled Wall Reinforced concrete wall to BS EN 1992 Low Low Acceptable Acceptable Acceptable Acceptable High Variable High Acceptable if the variable classification is due to surface water. The manufacturer s advice should be sought. Acceptable where: a) an appropriate cementitious multi-coat render or cementitious coatings are used; b) the wall is of concrete to BS EN Acceptable where: a) the piled wall is directly accessible for repair and maintenance from inside the structure; or b) the piled wall is combined with a fully bonded waterproofing barrier; or c) the piled wall is faced internally with a concrete wall to BS EN Acceptable Acceptable Acceptable Acceptable * The water table classifications are defined as follows: Low - where the water table or perched water table is assessed to be permanently below the underside of the base slab, this only applies to free-draining strata. Variable - where the water table fluctuates High - where the water table or perched water table is assessed to be permanently above the underside of the base slab. Ground permeability might affect risk under a low or variable water table Measures to reduce risk Use combined protection Incorporate appropriately designed sub-surface drainage and ensure that this is maintained Use a fully bonded waterproofing barrier Lower the permeability of the main structural wall Use concrete with a waterproofing admixture, e.g to BS EN 934 Ensure that discharge systems, e.g pumps, are maintained so that the system remains effective Waterproofing barriers This section describes in broad terms some of the options and issues associated with the choice of waterproofing system for domestic basements using Type A barrier protection. For more detailed guidance refer to BS 8102 and the Waterproofing Design Guide, by The Basement Information Centre. There are six categories of waterproofing barrier materials available. The following table shows where they can be located, subject to the form of supporting structure. In addition to those noted below, there are waterproofing membranes used in Type C construction. Table 3: Categories of barrier protection Categories External Sandwich Internal Bonded sheet membranes / / Liquid applied membranes / / Geosynthetic (bentonite) clay liners / / Mastic asphalt membranes / / Cementitious crystallisation slurries and powders Cementitious multi-coat renders, toppings and coatings / / / / Water stops Water stops are an essential part of the waterproofing design solution; for Type B protection used at the junction of structural panels, between walls and floors or along day-work joints for cast in situ concrete, the principle types can be classified as: a) Passive sections e.g. PCV water bars, located outside or within the structure to obstruct water transmission. b) Active strips or slurries (hydrophilic or crystallization) that react with water to prevent its further progression. These are set within the section of the structure, or post-injected. c) Specialist sealing resin injected into pre-positioned permeable hoses or similar. Design issues Particular attention should be paid to the specification of waterproofing systems - particularly for deep basements - relating to areas of high water table and in soils with aggressive chemicals. An appropriate specialist should be contacted for early advice and help on waterproofing design. Good design and workmanship are primary factors in achieving waterproof construction. Key considerations are compatibility of waterproofing systems, sealing around joints and junctions of the waterproof membrane and, for integral structural waterproofing systems, attention to the construction joints. Structural design may affect the choice of waterproofing and compatibility between the two is essential. For example, the stress and permissible crack width of a structure is controlled by reinforcement. In plain wall structures (i.e. not reinforced) the applied waterproof membrane needs to be appropriate to the anticipated movement of the structure, as the allowable movement or cracking may exceed the strain capacity of some waterproofing membranes. This is also a key consideration when refurbishing or extending basements, since movement between existing and new structures must also be anticipated. Details and construction profiles should be simple, avoiding nibs and thickening of structure wherever possible to prevent complicated junctions. Adequate details must be provided for each junction and considered in three dimensions (3D) for thoroughness. Although discontinuity with respect to waterproofing might be acceptable - subject to careful detailing and an appropriate assessment of risk - in practice this may not be allowed due to the need to manage radon, methane and other ground gases and contaminants. 12

13 Concrete construction Concrete is the most common and appropriate material used in the construction of new basement walls and floors. This is due in part to cost and availability but also its inherent resistance to water, durability under ground and ability to provide a stable structural surface for the support of waterproofing membranes. The method of construction chosen will depend upon consideration of various factors including: potential repetition of construction elements; accessibility for labour and cranes; cost; and fundamentally, the type of construction system permitted according to water table and use, as described in Table 2. Most forms of concrete construction can provide a variety of wall thicknesses to suit the particular structural requirements of each basement. Masonry construction or concrete blockwork Masonry construction or concrete blockwork is a traditional form of basement construction in the UK. It can be used with Type A waterproofing protection, for cases in which it is recommended that render or a similar smooth, continuous layer is applied to the blockwork face to provide continuous support to the waterproof membrane. Walls are typically reinforced and particular care is required at corner details and the wall slab junctions to cope with ground pressure. Masonry walls can also be effective as internal lining to create a drained cavity basement wall (Type C). Cast in situ concrete Cast in situ concrete is appropriate for all types of basement construction. It is a common form of basement construction for residential use, due to its relatively simple application, adaptability and cost. In-situ concrete is often the only appropriate form of construction for retrofit basements under existing properties, due to its relative ease of placement on site. As with masonry, in-situ walls are most commonly installed as reinforced structures but can be used plain (without reinforcement) following guidance provided in Addendum 1- Plain masonry and plain in-situ concrete retaining walls by TBIC. Typically, cast in situ walls are constructed with steel reinforcement bars to control cracking in the structure, with particular attention given to reinforcement of the corner junctions. Plain concrete walls are not generally specified as Type B construction due to the more critical need to control crack dimensions. Workmanship is a key issue for successful implementation of Type B protection. Water stops are included in the construction joints and particular attention is required with regards to day-working joints and the constituents of the concrete mix. Cast in situ concrete requires time to dry out before water sensitive finishes can be applied. Water-resisting concrete Concrete is inherently water-resistant and robust, making it suitable for subterranean construction. Its water resistance can be further enhanced by the introduction of admixtures. These admixtures (hydrophobic and pore blocking) act to reverse the capillary or sucking action of the tiny capillaries on the concrete surface and to effectively block the pores within the concrete when subjected to hydrostatic pressure. The result is a dry concrete that protects from water ingress. Such proprietary concrete mixes are available for this purpose from a number of specialist suppliers. Warranties can be obtained for products and workmanship on site. It is still possible for small levels of water vapour to pass through these types of concrete but they are generally very low and so unlikely to cause a problem. Additional membranes or ventilation may be considered, depending upon site conditions, proposed use and client or designers assessment of, and attitude to, risk. Insulating concrete formwork (ICF) ICF systems use either lightweight twin-walled expanded polystyrene (EPS) or extruded polystyrene (XPS) in panels or blocks to create formwork walls, for in-situ concrete walls, typically 100 or 150mm thick. Once in place, the formwork is filled with ready mixed concrete and, unlike conventional formwork, is left in place to act as insulation. For basement construction, polystyrene provides good background for waterproofing barriers. Care should be taken to ensure that the specification of the waterproofing membrane and its fixing methods are appropriate for application to polystyrene. ICF provides a cost effective, simple and inexpensive means for placing cast in situ walls; most appropriate for new build, rather than retrofit, basements. A new build basement using ICF. An example of concrete twin wall construction. 13

14 Precast concrete modular units Precast concrete units are increasingly used in Britain and elsewhere as a form of basement construction and provide an excellent support for waterproof membranes, either as a tanked membrane system or as the outer wall of a drained cavity or even as proprietary Type B system. Precast sections can be fabricated to specific design requirements for just-intime delivery, providing rapid on-site construction, integrated water bars, low site waste and high quality finishes. They are particularly appropriate for developments potentially benefitting from a high number of repeated standardised elements and the use of a crane on site. The waterproofing detail should be designed to suit the manufacturer s established method of joining panels. Twin wall This construction method is a hybrid of precast and cast in situ concrete walls and floors. Each wall unit comprises of two plates of precast concrete with a cavity between, linked by a lattice of steel reinforcement and placed on site; effectively as permanent concrete formwork. Once units and water bars are in place the cavity is filled with ready mixed concrete to complete the structural wall. Twin wall systems offer all the benefits of precast concrete described above but with the added benefit of continuous cast in situ concrete across the whole wall and, potentially, floor above. Concrete piles Piles are more commonly used for deep basement construction, rather than domestic situations and come in various forms, but can be useful for the creation of retaining walls to facilitate excavation in areas of restricted access or close to site boundaries. Secant or fair-faced contiguous piles can effectively become the outer wall of a Type C construction, or be faced with concrete or waterproofed to provide Type B or Type A protection. Further information on this and other forms of retaining structures can be found in The Concrete Centre technical publication Design and Construction of Concrete Basements. Concrete floors At basement level, floors are typically cast in situ concrete. The choice of system will be driven in part by coordination with the wall construction. Floors at ground floor level in housing can be constructed using a variety of different concrete construction techniques, including in-situ, block and beam, hollow core precast units or hybrid systems. Typically, it is possible and beneficial to span the full width of the basement space with the floor structure. Concrete easily exceeds the minimum building regulations requirements for fire and imposed loads and provides excellent sound insulation between the spaces. 14

15 Design issues Design principles The appropriate design of basements is well established and achievable, provided design and construction guidance is implemented. The general principle is to assess the risk of water reaching the below ground structure and to select an appropriate form of construction, structure and system of waterproofing to achieve the required internal environment. To do this the designer needs to understand the expectations of the client, the proposed and likely future use of the basement space and its associated performance requirements in terms of building regulations. It is essential that an appropriate site investigation is carried out to establish the soil and ground water conditions. Evaluation of these factors provides the basis for selection of an appropriate construction method, structural solution and system of waterproofing. It is strongly advised that a three dimensional (3D) review of structure and waterproofing is undertaken to identify and avoid any complex geometries, which will not be readily identified from normal twodimensional details. Basement design process (simplified) 1 Establish basement use; current and future flexibility 2 Site survey and exploratory works 3 Design proposals to define type of construction, water tight class and thermal performance 4 Detailed structural design integrated with design of waterproofing Roles and responsibilities Aspects of the design process are inter-related and there are likely to be a number of options available; particularly for straightforward residential properties. Minimising risk in basement design: Initial design should consider: Anticipated current and future use of basement Anticipated current and future ground water conditions Orientation of building relative to ground water Current and future daylighting and ventilation requirements Simplifying shape to facilitate waterproofing Location and access on site to facilitate construction Avoiding penetration of waterproof membrane for services where possible Site investigations should include: Appropriate qualitative assessment to appropriate depth Geotechnical investigation to indicate current and anticipated future ground water regime Tests to indicate soil properties and surface loading to establish lateral earth pressures Detailed design should consider: Correct choice of construction and waterproofing to suit ground conditions and use Integration of structural and waterproofing design to best practice recommendations Three-dimensional structural loads of building, ground and water pressure with attention to corners Access for future maintenance and alterations Obtaining specialist advice particularly for high water tables Construction should include: Supervision and checking (both essential) Experienced and skilled operatives Instigation of construction warranties In use: Maintenance and operation of drainage, pumps and ventilation systems Of particular importance for new-build basements is a unified approach to establishing an appropriate design solution and defining the roles and responsibilities of the design team from the outset. It was common for the design of the waterproofing system to be the responsibility of the architect however, in BS 8102: 2009 there is emphasis on including a specialist waterproofing advisor as part of the design team so that an integrated waterproofing system is created. This can be an architect or another consultant, manufacturer or supplier, provided they have the relevant expertise. An exception to this is when the construction method is classified as structurally integral protection ; when it may form part of the structural engineer s brief, a specialist waterproofing advisor may still be required. The client should be advised of any implications related to choice of construction and waterproofing with regards to the expected building use, future flexibility and associated maintenance requirements. 15

16 Basement use - current and future It is essential that the current and proposed use of a basement space is established early in design development, in order to provide the relevant performance criteria for the subsequent choice of waterproofing system, construction method and structural design. BS 8102 designates building uses against three grades of water tightness. These range from car parking areas, where some seepage and damp patches are tolerated, to ventilated residential and commercial areas where no water penetration is acceptable. Standards and forms of construction and waterproofing suitable for each grade of usage are provided. The previous edition of the British Standard (still referenced in the Approved Document - Basements for Dwellings) referred to Grade 4 environments. This was omitted in the later version since the only difference from Grade 3 is the performance level related to ventilation, dehumidification or air conditions. BS 5454 provides specific guidance related to the storage of exhibition or archival documents. Typical factors to be assessed in site investigation Existence of watercourse or seasonal position of water table Topography of land and direction of ground water movement Location of drains and land drains Soil type and conditions Movement risks - potential subsidence Presence of natural gases e.g. radon/methane Evidence of ground contaminants Boundary conditions A Grade 2 environment may be acceptable for permanent workshops or garages. However, since usage may change, it is better to construct a basement to a Grade 3 environment than to upgrade it later. In a high risk situation, the client and designer may wish to opt for additional waterproofing or vapour control. Site investigation The location and potential fluctuation of the water table is the key factor effecting basement design and construction. High water tables present the greatest risk for a basement and must therefore be identified at an early stage in the design. A watercourse or water table that rises and falls, and the potential for a perched water table, must also be identified. A high water table refers to, by definition, groundwater level consistently above the level of the basement floor. A permanently low water table involves a water table consistently below the level of the basement floor. A variable water table refers to levels varying between the two extremes. The installation of drainage systems can artificially lower the water table but is not always beneficial due to potential detrimental effects on neighbouring properties. Mirrors facing and adjacent to, window openings can significantly increase the perceived light levels. Courtesy of The London Basement Company. The draining ability of the soil and existence of contaminants can effect the choice of concrete construction and waterproofing method, as will the location of nearby drains and an assessment of the likelihood of their flooding. Table 4: Grades of basements Grade Basement Usage Performance Level 1 Car parking; plant rooms (excluding electrical equipment); workshops 2 Workshops and plant rooms requiring drier environment (than grade 1); storage areas 3 Ventilated residential and commercial areas including offices, restaurants etc; leisure centres Some seepage and damp areas tolerable, depending on the intended use* Local drainage might be necessary to deal with seepage No water penetration acceptable Damp areas tolerable; ventilation might be required No water penetration acceptable Ventilation, dehumidification or air conditioning necessary, appropriate to the intended use * Seepage and damp areas for some forms of construction can be quantified by reference to industry standards, such as the ICS s Specification for piling and embedded retaining walls. 16

17 Orientation and site layout The shape and orientation of a building should be considered because of the potential to dam the flow of ground water and the resultant build up of hydrostatic pressure. If unavoidable, additional subground drainage may need to be provided to discharge the water elsewhere. The form of construction of a basement and its cost will be influenced by the proximity of its walls to existing boundaries and adjacent buildings. The installation of external waterproofing and insulation, for example, requires sufficient space around the outside of the basement walls to provide a safe working area and may require temporary shoring. For new build constructions in tight - usually urban - plots, permanent underpinning of adjacent boundary walls or properties can allow valuable additional basement floor areas, but is expensive. An alternative is to install sheet piling to contain the ground supporting the structure while the new basement is under construction. Daylight The need to provide daylighting and comply with building regulation requirements for ventilation of habitable rooms will generally be met by incorporating openable windows in the same manner as above ground. This may entail adjusting the external ground levels in partially belowground basements, and would mean forming open areas for windows in fully below-ground basements. A primary factor in improving the quality of a room in a basement is the provision of natural light. Inclusion of glazed windows or doors provides greater possibility of future adaptation and uses, as well as sustainability benefits by reducing dependence upon artificial lighting. There are many techniques for improving the level of natural daylight and ventilation in basement spaces; determined by various factors including the proposed use of the space, proximity to boundary and plot size. Effect of building orientation on flow of ground water Flow of ground water Solutions for habitable spaces include simple direct lighting through windows, glazed doors or roof lights. Other supplementary solutions include the use of sun pipes or use of borrowed light with mirrors, glazed floors or stairwells. Daylighting techniques Partially sunken light wells and windows. Plan form of building avoids possibility of damming the flow of ground water Flow of ground water Full depth external spaces with glazed doors providing separate private amenity space and potential access to the garden or alternative entrance from the street. Sunpipes and pavement lights are suitable for basement spaces extending beyond the footprint of the building above. They provide permanent natural lighting with additional security but limited views. Glazed roof lights can wash spaces with natural light and provide sky views and natural ventilation if openable. Provide subground drain discharging to a suitable outfall to alleviate hydrostatic pressure where necessary Mirrors facing and adjacent to, window openings can significantly increase the perceived light levels and provide depth of field. Light and/or polished surfaces will generally improve the sense of space and daylight levels in a room. Glazed floors, particularly below upper floor roof lights or windows, can be useful additional sources of light but will require fire-rated glazing to maintain fire compartmentation between floors. Light from upstairs rooms can brighten lower ground floor spaces via the stairwell. This arrangement will depend upon the specific fire arrangements of individual properties and may require an upgraded fire resistance or detection system. Light from the upstairs room can brighten lower ground floor spaces via the stairwell. Image courtesy of Loates Taylor Shannon architects, Paul Avis photography. 17

18 Ventilation Building regulations require the provision of ventilation to all basements (heated or unheated) to adequately control moisture vapour, be it generated internally or brought through from the structure. Crossventilation or passive stack ventilation are the most effective forms of natural ventilation although continuous mechanical ventilation may be required depending upon proposed use and internal arrangement of rooms. For spaces with anticipated high levels of humidity, such as utility rooms, bathrooms or gyms, mechanical ventilation is essential. Ventilation should be directly applied to exposed external walls where possible i.e. not through the basement retaining walls. Stack ventilation (i.e. ventilation through a vertical vent duct) or mechanical ventilation which can be the preferred method of providing natural crossventilation, provided it does not compromise the fire compartmentation strategy of the development. This can be effectively provided by the staircase linking basement and ground levels, provided no fire separating doors are required. See the Building Legislation section of this document for more details. Basement ventilation Drainage It is advisable that drainage, or any service connections, should not be made through the basement retaining walls. Even if invert levels are lower than the outlet point, it is best to provide an up-and-over system, due to the potential for reverse flow. The location of utility spaces and bathrooms in basements has been facilitated by readily available pumped drainage systems and macerators. Consideration should be given to easy access for future maintenance and replacement. Structural design Coordination of the structural design with the construction and waterproofing system is essential. At a domestic scale, the correct masonry construction to back up Type A barrier protection may be determined from Approved Document Basement for Dwellings. Reinforced concrete walls and basement slabs, especially those used as Type B structurally integral protection, will require detailed structural calculations. The calculations take into account the ground, groundwater, the construction method and the required performance to determine the amounts of reinforcement required in the sections and specification of the concrete. Where piling is required, for instance as part of a Type C protection solution, then a more specialist design will be required and that must be integrated into the overall structural design. With respect to Type A protection, simple design i.e. with limited protrusions and corners will facilitate the installation of waterproofing membranes. Drainage and granular fill in front of the wall will minimise build up of hydrostatic pressure. Avoid in-plan inverted corners that face uphill they can trap groundwater. For advice on the structural design of basements, see Approved Document Basement for Dwellings [9], or, for larger basements, see Design and Construction of Concrete Basements [10]. The flow of air through a basement using natural cross-ventilation. Passive stack vent or mechanical vent Ventilation duct(s) The flow of air through a basement using passive stack or mechanical ventilation. Courtesy of TBIC 2004 [8] Natural ventilation and daylight provided with open two-storey design. Double height basement courtesy of ph+ architects. 18

19 Costs The cost of a basement, and its viability for construction as part of any development, will be determined by a number of factors including, most significantly, land value. Previous examples have illustrated how the inclusion of a partial or full basement can increase the potential floor area of a single dwelling and density of a whole development, thereby yielding higher returns. Analysis of the costs of constructing new domestic basements has been carried out by TBIC in 2005 and updated in 2010 [11]. The study provides approximate construction costs for basements based on a variety of parameters, including flat and sloping sites, full and partial basements, and in-situ concrete and masonry construction. The calculations are based on two-storey detached, semi-detached and terraced houses, with varying widths of frontage. The schematic design of a two-storey detached dwelling of 129m 2 is illustrated below, along with a similar area of house, designed over three storeys, one of which is a basement. The cost model exercise by TBIC concluded that building the three-storey version with a basement fully below ground, only cost an additional 3.8 per cent to construct and is even 0.8 per cent lower if constructed as a partial basement. Offset against the saving in land value through the reduced plot size, or the potential additional return from development of more plots on the same site, the cost exercise illustrates how basements can be a viable option for increasing profitable development, particularly in areas with high land values The schematic design of a two-storey detached dwelling of 129m 2. Plot area 264.5sqm Plot area 332.9sqm sqm house with habitable basement plus garage at the side 129sqm house without a basement requires approximately 26% more land 3.0m increase in size width The empty shell specification basement An idea resulting from the cost analysis is that a basement, or semibasement, completed to a very basic, or empty shell space specification, can yield even greater potential profit margins for housebuilders, whilst offering a reduced cost for the purchaser. This is an attractive proposition, since the basement offers an economic and realistic way of creating a large single room, with the flexibility for future adaptation to suit the lifestyles and requirements of the occupants. The concept of providing spaces, or a blank canvas, for residents to adapt to their specific needs sits well with the concept of design based on resource efficiency and minimising waste to landfill. Elemental breakdown of construction Factors affecting the cost of basement construction include ground conditions such as excavation costs, type of waterproofing system and access for construction. The TBIC cost analysis [11] provides an elemental breakdown of the range of costs associated with basement construction and summarises the varying influencing factors including type of basement, construction type, plan form and sloping site. Ground works associated with basement construction can amount to between 18 and 44 per cent of overall construction costs. There is potential scope for cost savings to be made, such as retention of excavated soil on site for landscaping, or adoption of an empty shell specification leading to a reduction in fitting-out costs. Table 5: Extract summary of costs for basement construction as a percentage of construction costs [11]. Groundworks Fitting-out Fully finished 18-34% 29-47% Empty Shell 27-44% 10-19% 19

20 Building legislation Building regulations Building regulation approval is required for the construction, adaptation and extension of all basements. Comprehensive guidance on all building regulations related to basement construction is provided by the Approved Document - Basements for Dwellings produced by TBIC. When planning new basements for housing, particular attention is required to the provision of fire separation between the basement and ground floor, a fire escape from the basement and disabled access and entrance. Below is a summary of the issues related to basements under two-storey houses with typical floor to ceiling height. Designers should consult the relevant approved documents to check requirements related to their specific design and for other housing types. Fire resistance and separation The basement, as defined above, is not counted when assessing the numbers of storeys for fire resistance and means of escape. Typically, for a two-storey house over a basement, 30 minutes fire resistance is required for the structure, increasing to 60 minutes where the number of storeys is four or more. Both requirements are easily exceeded using concrete. Fire separation between the basement and upper storeys is required if the height of the top floor is more than 4.5 metres above the lowest external ground level. This situation is only likely to occur in two-storey dwellings if the basement floor level is less than 1.2m below the external ground level, or located on a very sloping site. The 30-minute separation required can be simply and cost effectively achieved using concrete. The walls and floor between garage and house requires 30 minutes fire separation which also applies if located in a basement. Health and Safety As with all forms of construction, consideration of health and safety issues is required at all stages of design and construction. Particular issues related to the construction of basements depend upon the exact nature of the work, but may include working in confined spaces, falls from height, temporary stability and craning of large structural elements. Planning permission Currently, planning permission is required for the construction and extension of basements, even when not visible above ground level. At the time of writing, the extension of a property below ground is not directly covered by permitted development rights but submissions have been made to address this apparent anomaly. A detailed analysis of the role of basements within the planning guidelines of the UK has been produced by TBIC and is published on their website as The Hidden Potential. Basements: a planning review document. Size of development While planning approval is required for the construction of a basement, often the size of the proposed construction below ground is less contentious than an over-ground structure. This is particularly useful for increasing the proposed floor area of an existing or new property in areas with strict planning policy controlling the construction of new buildings, such as a National Park or Conservation area. In-fill development in urban settings can also benefit from the accommodation and value added by inclusion of a basement. Ground floor flats or maisonettes with a basement level and direct main entrances require no fire separation over and above typical fire separation between apartments. Since concrete floor construction can easily provide the fire and acoustic separation needed for a separating floor, it can be possible to convert basements into separate dwellings, provided all the necessary fire escapes and ventilation etc. are provided, where such floors are utilised. Means of escape Habitable rooms in basements require a safe means of leaving the building. This could be provided by the main stair of the house, provided it is protected and is connected to a final exit. Alternatively, escape can be provided by an additional stair, leading to an alternative final exit. The stair can be internal, but more commonly external. Escape through windows is also permissible if designed to permit escape as defined by the building regulations. The last two options offer cost effective solutions, particularly in terms of optimising usable space, provided the external stair is positioned away from other windows. It is worth noting that non-habitable rooms, such as kitchens, utility rooms and bathrooms can be classed as inner-rooms and, depending upon the layout, may not require separate means of escape. It is permissible to exit into gardens or courtyards, provided they have an exit to a place of safety or are at least as long as the height of the house. New Forest House, designed by Perring Architecture and Design. Photographer: Nigel Rigden. 20

21 A low energy house, recently constructed in the New Forest National Park was limited above ground to the size of the original existing single-storey structures on site. Development of the three-bedroom family home was possible through the construction of a large basement, containing study area, two double bedrooms, wine storage and plant area, and a large library and TV room. Increased density As described in section Optimising potential development, the inclusion of a basement level can assist in obtaining planning permission by raising the density of a development through increasing the number of homes without reducing the amenity levels. Flood risk areas There is a resistance, through planning controls and the insurance industry, to build houses on areas prone to flooding. The provision of any habitable rooms in basements in flood risk areas is generally not supported by planning legislation but can be feasible if addressed directly. For example, the provision of an escape stair to an area above the flood risk level could be an acceptable solution, rendering the proposed development feasible with basements. The construction of concrete ground structures or sacrificial basements is a recognised solution for construction in areas of high flood risk. The habitable spaces are raised a minimum of 600mm above the level of design flood risk, while the basement area can provide additional nonhabitable storage space. Concrete is a flood resilient material and the design and construction of the basement and ground floor can deliver best practice both in terms of water-entry prevention to the habitable areas and recovery from the effects of flooding. Floating concrete basements have been pioneered in the Netherlands, where 48 floating homes have been constructed in Maasbommel on the banks of the Maas, by Dura Vermeer [2]. Party Wall Act The Party Wall Act exists to protect the concerns of neighbouring landowners and to facilitate an agreements between them with regards to construction works. It will most likely be necessary to issue a Party Wall Notice, as required by the Act, if a basement is being constructed or extended. The diagrams below show the summary of criteria for serving Party Wall Notice. Summary of criteria for serving Party Wall Notice under the Party Wall Act 1996 [13]. Less than 6m Less than 3m Adjoining Owner Adjoining Owner 45 o Building owners excavation Building owners excavation New structure is less than six metres away and lower than a line drawn downwards at 45 o from the bottom of the neighbours foundation. Excavation and construction of foundations and basement walls within three metres of an adjacent building or structure owned by others. 21

22 Appendix Basements and credits scored under Code for Sustainable Homes Section Benefit potential through basements Associated credits The role of the basement Energy/ CO 2 Drying space 1 Potential space to house a permanent fixture for four to six linear metres of drying space, where external options are not practical or in addition to external options for use during inclement weather. Suitable ventilation is required to comply with Building Regulations Approved Document F Ventilation and is equivalent to requirements applying to a bathroom or utility room. Bicycle storage 2 Space for secure, dry storage of bicycles. Direct access to a public right of way is required, either via stairs at the front of the house or via the garden. Home office 1 Ideal space to accommodate the home office requirement of a minimum 1.8m wall length to allow for a desk, chair and filing cabinet. The office would need a window with an opening casement window of 0.5m 2 in order to provide ventilation and have a daylight factor of at least 1.5%. (This provision more than satisfies the requirement for an alternative means of escape as defined by the building regulations). The inclusion of a home office in the basement will influence the daylighting factor for the overall dwelling under the Health & wellbeing section. Fuel storage None directly. Supports potential up to 2 points. A basement can also provide storage for biomass materials. While this does not attract points directly, it supports the use of biomass heaters and combined heating and power (CHP) plants which help score points under the Energy and Efficiency calculation. Materials Surface water run-off Waste Space for waste storage The environmental impact of the ground floor of the basement would be assessed on the elements contained in the BRE Green Guide Domestic Ground Floor Construction. At the time of writing there is no Green Guide rating for a ground floor designed as a basement. The CSH is likely to need to make an individual assessment of the specific construction. The floor at ground level in the dwelling (i.e. between basement and first floors) would be assessed as an Upper Floor Construction in the BRE Green Guide. Basement walls represent the substructure of the dwellings and are currently not considered in the CSH assessment of environmental impacts. The external walls above the basement would be assessed against the External Wall Construction elements contained in the BRE Green Guide. Any internal walls or separating walls would be assessed against the relevant building elements in the BRE Green Guide. 1 The inclusion of sacrificial basements in houses with a medium to high level of flooding risk could support gaining an additional point. The basement raises the ground above the design flood level, while providing additional non-habitable storage space below. 4 In order to obtain credits the facilities need to be adjacent to the kitchen and positioned for disabled access. Health and wellbeing Daylighting 3 To maximise the number of points available, this would require all living rooms, dining rooms or studies that may be located in a basement to also have a daylighting factor of 1.5%. If a kitchen is located in the basement, this must have a daylight factor of 2%. To gain additional points, these rooms would also require 80% of the working plane in each room to receive direct light from the sky. Sound insulation 3 or 4 A basement in a detached house would score maximum points in this area [4]. Basements provide excellent sound insulation. Where a basement contains separating walls between dwellings, these can be built to existing Robust Details specifications where the appropriate concrete / masonry wall construction will allow the highest score ( three credits) currently available for adjacent dwellings. Full use of Robust Detailing credits depends, however, upon the external wall construction and flanking conditions. Solid external concrete walls can provide good acoustic insulation, but at the time of writing are not included as a Robust detail. Private space 1 External courtyards at basement level count as private external space. Ecology Optimise foot print 2 A basement can increase the footprint ratio of the net internal floor area over the net ground floor of most standard design houses to achieve at least 2.5:1 and often 3:1. The latter allows maximum points to be scored under the Code. Use of basements and potential sustainable homes credits For further information on the Code for Sustainable Homes and how to use concrete and masonry as part of the solution, refer to Energy and CO 2 masonry solutions and Concrete and the Code for Sustainable homes, both available at 22

23 References 1. BRITISH STANDARDS INSTITUTION. BS (2004) Building and Civil engineering - Vocabulary General Terms. London, BSI, 2009 pp CLG Approved Document B (fire safety)- Volume 1: Dwelling Houses (2006 Edition). Appendix E Definitions. London, HMSO, 2006 pp NHBC FOUNDATION Risks in domestic basement construction NF4. NHBC Foundation, Amersham, 2007 pp TRADITIONAL HOUSING BUREAU Attitides towards house construction - MORI survey (pp. 25) 1999 (pp. 30) and 2001 (pp. 30) 5. THE BASEMENT INFORMATION CENTRE: Approved Document: Basements for Dwellings. Section 5 (update pending) TBIC, Blackwater, 2010 (ref TBIC/001) 6. THE BASEMENT INFORMATION CENTRE Thermal Performance of houses with basements (Based on the Regulations and SAP in-place at the time of this publication). TBIC, Blackwater, pp. 24 (Ref: TBIC/005) 7. BRITISH STANDARDS INSTITUTION BS 8102 (2009) Code of practice for the protection of structures against water from the ground pp THE BASEMENT INFORMATION CENTRE Approved Document: Basements for Dwellings, TBIC, Blackwater, 2005 pp (Ref TBIC/001) 9. THE BASEMENT INFORMATION CENTRE Approved Document: Basements for Dwellings, TBIC, Blackwater, 2005 pp (Ref TBIC/001) 10. NARAYANAN R S & GOODCHILD CH, Design and Construction of Concrete Basements, MPA - The Concrete Centre, due THE BASEMENT INFORMATION CENTRE, Cost study of Houses with Basements, TBIC, Blackwater, 2010 (pending) 12. Innovation and Research Focus Issue 65 May 2006, pp CLG The Party Wall etc Act 1996: explanatory booklet 02 BR pp.18 Further reading BS 8102: Code of practice for the protection of below ground structures against water from the ground, revised and re-issued in 2009, provides guidance on methods of dealing with, and preventing the entry of water from, surrounding ground into a building below-ground level for all below ground structures. Basement waterproofing: Design Guide and Basement Waterproofing: Site Guide by the former BCA, offers comprehensive basic guidance on design, use and application of different water-resisting methods and systems. The Design Guide is being revised for issue by TBIC, with support from The Concrete Centre, The CIRIA Guide: Water-resisting basement construction - a guide safeguarding new and existing basements against water and dampness, (Report 139) provides additional comprehensive guidance, with a useful summary provided by Report 140. Approved Document Basements for dwellings brings into one document all of the relevant building regulations for dwellings that are affected by the inclusion of a basement and is supplemented by Approved Document - Basements for dwellings. Addendum 1 Plain masonry and plain in-situ concrete retaining walls. British Board of Agrément certificates are available for some water membrane products, which are not covered by the British Standards for asphalt or bituminous felt and for basement tanking systems. Design and Construction of Concrete Basements will provide comprehensive guidance on the design issues for the design of deep basements, focusing on structural calculations. To be published by MPA - The Concrete Centre in IHS BRE Press. Good Building Guide 72, Parts 1 and 2. September 2007 are short publications providing some practical guidance on a range of issues associated with basement design and construction, some replicating information from the Approved Document Basements for Dwelling. 23

24 The Concrete Centre, Riverside House, 4 Meadows Business Park, Station Approach, Blackwater, Camberley, Surrey GU17 9AB Ref. TCC/04/12 ISBN First published 2010 MPA - The Concrete Centre 2010 Courtesy of Loates Taylor Shannon, Paul Avis photography. The Concrete Centre is part of the Mineral Products Association, the trade association for the aggregates, asphalt, cement, concrete, lime, mortar and silica sand industries. All advice or information from MPA -The Concrete Centre is intended only for use in the UK by those who will evaluate the significance and limitations 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 by Mineral Products Association or its subcontractors, suppliers or advisors. Readers should note that the publications from MPA - The Concrete Centre are subject to revision from time to time and should therefore ensure that they are in possession of the latest version. Printed onto 9Lives silk comprising 55% recycled fibre with 45% ECF virgin fibre. Certified by the Forest Stewardship Council.