EXTRA. NHBC s technical newsletter April 2002 Issue 23. This edition includes:

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1 NHBC s technical newsletter April 2002 Issue 23 This edition includes: Major changes to NHBC glazing Standards Glazing requirements amended to improve the durability of insulating glass units. Changes to NHBC Standards to align with Approved Document L and Robust Details Detailed changes made to a number of Chapters. Changes to NHBC Standards Chapter 6.8 to align with Approved Document J Chapter 6.8 now revised to ensure chimney and flues meet the new AD. What is the expected life of my new home? What durability is NHBC looking for? Use of non-entry inspection chambers Are deep inspection chambers accepted by NHBC? EXTRA STANDARDS EXTRA 1

2 CONTENTS 2 Major changes to NHBC glazing Standards 3 Approved Document L and Robust Details 3 Approved Document L - Commissioning central heating systems 3 SAP Standards Chapter 6.8 Fireplaces, chimneys and flues 4 Flooring - fixing and perimeter support 5 Timber frame certification in Scotland 5 What is the expected life of my new home? 6 Non-entry inspection chambers 6 Preparing for Floods 7 Concrete in aggressive ground 7 Pavers - which pattern is appropriate? 8 Questions & Answers Major changes to NHBC glazing Standards For more than two years NHBC has been providing cover for multiple glazing. It is now appropriate that the Standards for glazing, contained in Chapter 6.7, Doors, windows and glazing, should be reviewed and amended to reflect changes to recommended practice. This article explains what the changes are, but house builders are asked to look at the revised pages of the Chapter for further details. These are enclosed separately. The main changes are: Insulated glass units (IGUs) will need to meet the requirements of BS EN 1279, Glass in building-insulating glass units. This is the new European standard which will replace BS 5713, Specification for hermetically sealed flat double glazed units. Units to BS 5713 will continue to be acceptable until BS EN 1279 is published. Publication is expected later in IGUs should now be specified as having dual seals - single seal units will no longer be accepted. This change is intended to ensure significantly improved durability. Desiccant should be provided to every section of spacer bar. All IGUs are now required to have third party certification (e.g. Kitemarking). This applies to IGUs installed in all types of frame, including timber windows and windows fabricated under a BBA certificate. Site glazing is still permitted, but the bottom bead must be drained and ventilated. Solid bedding is accepted only for factory-glazed windows and doors where the IGU is up to 1m 2 in area. For factory-glazed windows and doors having IGUs over 1m 2 in area, the bottom bead must be drained and ventilated. It is important that NHBC inspection staff and others can verify whether the units and glazing meets with the new standard. Some aspects have to be marked on the unit or the window itself. This is often a requirement of the unit or window standard, and by not marking the manufacturer is not conforming. IGUs Marking Units to BS EN 1279 / BS ) Manufacturer s name or trademark. 2) The number of the British Standard i.e. BS ) The Kitemark. Where On the glass or spacer bar of every unit in such a way that the marking can be seen after the units are installed. Windows Marking BS 7412 for PVC-U windows 1) Manufacturer s name or trademark. 2) The number of the British Standard i.e. BS ) The Kitemark. Where In an unobtrusive position such as between the casement and frame. Marking BBA certificated windows Each window should have a label bearing the manufacturer s name or trademark and the BBA identification mark incorporating the certificate number. The new requirements will become effective from 1 October Ensure that you are fully aware of the detailed changes, and that the correct windows and IGUs are being purchased and used on site. 2 STANDARDS EXTRA

3 Approved Document L and Robust Details In Standards Extra 22 we advised of the publication of the 2002 edition of Approved Document L (AD L), Conservation of fuel and power (England and Wales), and the separate publication, Robust Details to which it refers. A major review of the NHBC Standards has been necessary to ensure that they align with both AD L and Robust Details. Although a total of nine chapters have needed some amendment, the main changes are to Chapters 6.1, External masonry walls, and 6.2, External timber framed walls. The main changes to NHBC Standards are: Door and window openings now require better sealing to prevent air leakage. Additional precautions to prevent cold bridging particularly at lintels and reveals. Sealing of sole plates of timber frame construction to prevent air leakage. Amendment to the minimum dimension for ventilation paths in cold pitched roofs. References to Robust Details, particularly in Chapter 5.2, which deals with suspended floors of both concrete and timber. AD L and the Robust Details only apply under the Building Regulations in England and Wales. In Scotland, Part J has been amended to refer to the latest edition of the BRE publication, Thermal Insulation: avoiding risks. Currently in Northern Ireland, the regulations have not changed. However, it is likely they will be amended in a similar way to those in England and Wales in due course. Builders in England and Wales should note that the 2002 edition of AD L comes into effect on 1 April, and will be applicable to some homes started before October Stop press On DTLR's behalf, the Building Research Establishment has set up a "Frequently Asked Questions" internet site as a means of delivering answers to questions that are being raised in connection with Approved Documents L1 and L2. The address is: Builders should familiarise themselves with the changes to NHBC Standards which are effective for all homes from 1 October Approved Document L - commissioning central heating systems, the Benchmark scheme. One of the changes to the 2002 edition of Approved Document L (AD L), is a new requirement for heating and hot water systems to be inspected on completion, and commissioned to ensure that they are operating efficiently. At the same time a 'suitable commissioning certificate' is to be issued to confirm this. AD L specifically refers to the certificate published by Benchmark, as being suitable. A copy of the Benchmark certificate is supplied with over 90% of all gas boilers currently sold in the UK. Benchmark certificates should be completed by suitably qualified certifiers, such as CORGI registered installers for gas, OFTEC registered technicians for oil, and HETAS registered installers for solid fuel systems. Further information on the Benchmark Scheme is available from the Central Heating Information Council at For homes built to the new AD L ensure that a suitable commissioning certificate, such as that produced by Benchmark, is completed for each installation. SAP 2001 The latest version of the Government s Standard Assessment Procedure (SAP 2001) is now available. It replaces the 1998 edition. The main changes are: the Carbon Index is introduced (this is a new means of showing compliance with the 2002 edition of Approved Document L) the upper limit of the SAP rating is raised from 100 to 120 the SAP indexing function is revised to make the rating less dependent on floor area some additional heating systems are included data tables are updated (including those for boiler efficiency and heating controls) U-values should be based on European Standards. Until 30 June 2002, builders may use either SAP 1998 or SAP 2001 to calculate energy ratings notified to the building control body. Energy ratings notified on or after 1 July 2002 must use SAP Where the energy rating was calculated using SAP 1998 and notified to the building control body before 1 July 2002, the SAP rating on the notice displayed in the home must be to SAP Builders may however, display the SAP 2001 rating (on the expanded scale) in addition. Further information and a downloadable version of SAP 2001 is available at A copy of DTLR circular letter to building control bodies is also available at STANDARDS EXTRA 3

4 Standards Chapter 6.8, Fireplaces, chimneys and flues The Standards update pack includes pages to update Chapter 6.8, Fireplaces, chimneys and flues, to reflect changes in the 2002 edition of Approved Document J (AD J), Combustion appliances and fuel storage systems. The main changes to Chapter 6.8 are: Notice plates, containing safety information, are now required to ensure the correct application and use of the hearth and flue. Hearths have to be marked so that home owners do not apply combustible floor finishes, such as carpets, too close to the appliance. One way of achieving this is to provide a change of level at the hearth. Outlet positions from flues for solid fuel, gas and oil have changed. In particular, positions for flue outlets adjacent to a boundary have been changed. Ventilation requirements have been changed for solid fuel, gas and oil appliances. Concrete flue liners should now meet with a draft European standard. Although the changes to AD J apply in England and Wales only, it is likely that similar changes will be made to Regulations in Scotland and Northern Ireland in due course. NHBC takes the view that notice plates are a sensible way of giving home owners essential information on the safe use of the flue and hearth for the life of the home, and so NHBC is also applying this requirement in Scotland and Northern Ireland. An example of a notice plate is shown above. Plates should be installed in an obvious position that need not be intrusive, such as: next to the electricity consumer unit, or next to the chimney or hearth, or next to the water supply stop valve. The plate should be robust, legibly and permanently marked and securely fixed. Builders in England and Wales should note that the 2002 edition of AD J comes into effect on 1 April, and will be applicable to some homes started before October Builders should familiarise themselves with the changes to Chapter 6.8, which are effective for all homes from 1 October Flooring fixing and perimeter support Fixing of flooring Squeaking floors are a regular source of irritation to home owners and amongst the most common complaints. It can be exceptionally difficult to put problems right in occupied homes, particularly where carpets have been laid and rooms are full of furniture. To reduce the incidence of squeaking floors, NHBC has decided to adopt the recommendations of BS 7916, Code of practice for the selection and application of particleboard, oriented strand board (OSB), cement bonded particleboard and wood fibreboards for specific purposes. This calls for boards to be glued together and to be glued to the floor joists. The appropriate adhesive for both operations is polyvinyl acetate (PVAC). The chipboard or OSB manufacturer should be able to advise on specific recommended products. The adhesive is required in addition to mechanical fixings, which should be provided as specified in NHBC Standards, Chapter 6.4. Perimeter support to chipboard flooring We are often asked whether perimeter support to chipboard flooring needs to be provided in all situations, and builders have queried whether perimeter support can be left out if thicker boards are used on closely spaced joists. NHBC Standards are taken from BS 7916 and the matter has been referred back to the BSI committee responsible. That committee has concluded that chipboard flooring should always be supported at the perimeter, regardless of the thickness of the boards and the spacing of the floor joists. Perimeter noggings should be provided for all chipboard floors. If you are using chipboard or OSB floor decking, joints between boards should be glued and boards should be glued to the floor joists. The new requirements will come into effect from 1 October STANDARDS EXTRA

5 Timber frame certification in Scotland NHBC has made an administrative change to form HB210, Timber Frame Construction, which is used in Scotland. Until now completed forms have been delivered to NHBC s Scottish office. In future the form should be given by the certifier to the house builder who should make it available to NHBC inspection staff on site. Timber frame certifiers can obtain the new forms from either the NHBC Edinburgh office, or NHBC Technical in Amersham. Certifiers may use up supplies of old forms, but should follow the new procedure and send the completed form to the builder. When building timber frame dwellings in Scotland, ensure that a completed HB210 form is available for NHBC inspection staff on site. What is the expected life of my new home? This is a question we are often asked in NHBC Technical. Until quite recently, most homes have been built of conventional construction, usually with an outer leaf of brick and inner leaf of blockwork or timber frame. The notional design life is sixty years but with proper maintenance there is no reason why homes should not last much longer and many do. There are, of course, certain parts of the external envelope, which have a lesser design life and which may need planned maintenance and possible replacement. Examples are flat roof coverings and doors and windows. Home owners are generally aware of these limitations and accept them as part of the ongoing commitments they have to budget for. As a consequence, NHBC has not in the past specified a period for the design life or durability. More recently we have received proposals from manufacturers and builders to use novel or innovative building systems, products and materials, including some with a design life considerably less than that of conventional construction. Although Buildmark provides cover for ten years, NHBC Standards start from the presumption that home owners (and their mortgage lenders) should get homes which are reasonably durable, and certainly well beyond the tenth year. To reflect this, a change has been made to Technical Requirements R3 (Materials Requirement) and R5 (Structural Design Requirement) to ensure that homes are designed with a durability of at least 60 years for the structure. This is not likely to have any implications for traditionally constructed homes of masonry or timber frame. Note the changes to Technical Requirements R3 and R5. Builders intending to construct homes where durability may differ from the norm should discuss their proposals with NHBC Technical at the earliest opportunity. These changes apply immediately. STANDARDS EXTRA 5

6 Non-entry inspection chambers The recent introduction of a non-entry inspection chamber by a major manufacturer has caused much discussion. Other manufacturers are also known to be developing similar products. Picture supplied by Wavin Plastics Ltd. What are non-entry inspection chambers? As the name suggests, these are chambers for which all access for maintenance of the drain (i.e. rodding) is achieved from the surface. For health and safety reasons, they have a restriction just beneath the cover to deter human entry. How deep can the inspection chamber be? A new British Standard BS 7158, Specification for plastics inspection chambers for drains, is for plastic inspection chambers up to 6m deep from cover to invert. However, the one currently on the market is limited to a maximum depth of 3m, which in practice is sufficient for most housing developments. As the invert depth increases, the pressures on the chamber increase, so to avoid the risk of collapse the maximum depth recommended by the manufacturer should not be exceeded. Do they meet with Building Regulations? Non-entry inspection chambers are referred to in the new 2002 edition of Approved Document H (AD H) for England and Wales, and BS EN 752, Drain and sewer systems outside buildings. Table 11 of the AD specifies suitable dimensions for the chambers and covers, and Table 13, the maximum spacings. The maximum distance between chambers should not exceed 45m, although in most housing developments chambers are likely to be much closer. Part M of the Building Standards (Scotland) and Part N of the Northern Ireland Building Regulations do not currently recognise the use of non-entry inspection chambers. Can non-entry inspection chambers be used by NHBC registered builders? If non-entry chambers meet with BS 7158 for a specified invert depth, then they can be used. The invert depth should not exceed that specified by the manufacturer (3m for the product currently available). If you intend to use non-entry inspection chambers, ensure they meet the above criteria, and that the maximum distance between them does not exceed 45 metres. Preparing for Floods Interim Guidance for Improving the Flood Resistance of Domestic and Small Business Properties. As Standards Extra 23 goes to print, this new DTLR document is being published as Interim Guidance. Recent flooding events across the UK have had a devastating impact on many lives and businesses. Unfortunately the risk of flooding cannot be eliminated. The new guide, for the first time in a single publication, collates best practice guidance on measures for improving flood resistance of new and existing properties that are at risk. The guide is for existing home owners and small businesses with properties at risk of flooding, as well as for developers, builders, local planning authorities, building control bodies, and others involved with new construction or with renovation in areas of flood risk. It deals with assessing the risk, with temporary and permanent measures to prevent or reduce floodwaters entering a building, and with improving the flood resistance of the building. Real life case studies are also provided. The guide also gives an overview of PPG 25:Development and Flood Risk, and of the types of construction most appropriate for developments at risk of flooding. NHBC is one of several organisations that assisted in the funding of this project, led by WS Atkins Consultants Ltd. Information was drawn from a range of official sources as well as home owners, small businesses and builders. Free copies will be available from the Environment Agency's Floodline on , and electronically via the DTLR website. 6 STANDARDS EXTRA

7 Concrete in aggressive ground The industry specification for concrete at risk from sulfate attack has been defined for the past decade in BRE Digest 363, ''Sulfate and acid resistance to concrete in the ground''. Information obtained from a study of sulfate attack on concrete road bridges has led to a better understanding of the specification needed to resist chemical attack. As a result, BRE Digest 363 was withdrawn and replaced, in August 2001, with the four part BRE Special Digest 1, ''Concrete in aggressive ground''. Sites now need to be classified in terms of their Aggressive Chemical Environment for Concrete (ACEC). This is derived from the site investigation and is based upon: the sulfate content of the soil and groundwater the presence of mobile or static groundwater the acidity of the soil and groundwater and whether the site is natural or brownfield. Once the ACEC has been ascertained, the Design Chemical Class (DC Class) of the concrete can be determined. This provides the performance requirement for the concrete for the specific site conditions. The DC Class, which could be compared with the Sulfate Classes in the old BRE Digest 363 for certain acidic and ground water conditions, is determined from the ACEC, but consideration also has to be given to: the Structural Performance Level of the element (e.g. low where the element is for house foundations and high where the element is for structures retaining hazardous materials) the section thickness of the element the Additional Protective Measures provided to the element (e.g. surface protection or sacrificial layer). With the DC Class established, the concrete grade can be selected in accordance with the soon to be revised BS 5328, ''Concrete''. In general terms a concrete that was suitable to satisfy the requirements of Class 1 or Class 2 sulfate conditions under BRE Digest 363, is also likely to satisfy Design Chemical Classes DC1 and DC2 respectively. The changes incorporated in Special Digest 1 will be reflected in a revised BS 5328 which is due to be published later this year. Ultimately, in December 2003, it is likely that BS 5328 will be replaced with a new package of standards. This package will include the current BS EN 206, ''Concrete'' and BS 8500, ''Concrete'' which is in preparation. NHBC s Standards will be amended to reflect changes to the British Standards as they become available. Until then, concrete should be specified in accordance with the new guidance in BRE Special Digest 1. Concrete should be specified in accordance with BRE Special Digest 1 and the new BS Ready mixed concrete suppliers will be able to provide suitable concrete mixes for appropriate DC Classes. Pavers - which pattern is appropriate? Clay and concrete paver blocks are becoming a popular choice for builders when looking to enhance the visual appeal of a property. The paver has also become a sustainable alternative to the use of tarmac, with its surface water drainage capabilities. When installing this type of finish builders should be aware that the laying pattern needs to be appropriate for the likely traffic. There are a number of patterns that can be used but, a number of these should not be used for areas subject to vehicular traffic. British Standard 7533 "Code of practice for laying precast concrete paving blocks and clay pavers for flexible paving" states: "Where rectangular units are being used in areas subject to vehicular traffic, herringbone pattern should be used to minimise creep and to ensure better distribution of imposed wheel loads. Basket weave pattern should only be used in pedestrian areas. Running bond pattern is usually confined to pedestrian areas but has been successfully used in areas subject to occasional light vehicular traffic" The Brick Development Association ( Design Note 9 gives similar advice and paver manufacturers who hold BBA certification for their products state that the bond for rectangular pavers should be herringbone. 45 degree Herringbone 90 degree Herringbone Running Bond Basket Weave To ensure creep of the pavers is kept to a minimum, they should be laid in accordance with BS 7533, which recommends that herringbone pattern should be used in areas subject to vehicular traffic. Running bond should only be used for pedestrian areas or private driveways. STANDARDS EXTRA 7

8 Questions & Answers Below are the answers to a selection of questions we have recently been asked in NHBC Technical. Noggings for lateral restraint straps Question Can noggings to lateral restraint straps be kept down from the top of the joists to accommodate services? Answer NHBC Standards clause 6.4-S10 requires full depth noggings where lateral restraint straps are fixed to the underside of joists and noggings of at least half depth where the straps are fixed on top of the joists. In both cases the noggings are in contact with the straps. However, these arrangements can be difficult to accommodate services. full depth packing 50mm max reduced depth nogging where there are services service restraint strap at either the top or bottom of the joists full depth noggings where there are no services Noggings act as struts to resist movement of the wall and should not be weakened by excessive notching or drilling. Where services are located in the top of the floor zone and are obstructed by a nogging, that nogging may be kept down from the top of the joists by 50mm. Adjacent noggings/packing should be the full depth of the joist as shown in the diagram above. Gaps around PVC-U windows Question What is the maximum gap that should be permitted for sealant around a PVC-U window? Answer A gap should be provided to allow for thermal expansion of the window. A gap of 5-10mm (evenly distributed) should be provided around PVC-U windows. In the case of large windows or patio doors a maximum gap of 15mm may be permissible. Dpc trays to rendered walls Question On fully rendered masonry walls, do cavity trays need to be provided over openings? If so do they require weepholes and stop ends? Answer Wind driven rain may penetrate rendered masonry through minor cracks, around openings, and at architectural details. Cavity trays with stop ends are required over all openings. Weepholes do not need to be provided where masonry walls are fully rendered. End support to chipboard flooring Question Where end joints in chipboard flooring occur between joists, how should the joints be supported? Answer End joints should usually be located over a joist; failure to provide adequate support will significantly weaken the floor. For all thicknesses of flooring, joist centres and types of chipboard, an H frame should be provided under all end joints occurring between joists. The frame should be securely fixed to adjacent joists. 8 NHBC Technical Buildmark House, Chiltern Avenue, Amersham, Bucks HP6 5AP Tel: Fax: technical@nhbc.co.uk HB /03