NHBC’s technical newsletter December 2004

Issue 31

This edition includes: 2

Downlighters in ceilings below roof spaces We look at the implications of the trend in using downlighters in ceilings

Locks to individual flat entrance doors NHBC resolves the potentially conflicting requirements for security and safety for entrance doors

4

Attic trussed rafters Due to the popularity of utilising attic space, we spell out where services must be routed to maintain structural integrity of attic trusses

4

Flood risks CIRIA publication provides practical guidance on flood risks

6

New Approved Document P and changes to Documents A and C (England and Wales) A quick run down of the main changes in the new regulations

EXTRA

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CONTENTS

2 Downlighters in ceilings below roof spaces 3 Locks to individual flat entrance doors 4 Flood risks 4 Attic trussed rafters 5 Door limitation devices – flat entrance doors 5 Building for tomorrow 2005 6 Building Regulations in England and Wales – New Approved Document P and changes to Approved Documents A and C 7 EcoHomes 7 Air Admittance Valves (AAVs) 8 Questions and answers

Downlighters in ceilings below roof spaces The installation of open downlighters in ceilings under roof spaces has become very fashionable. Unfortunately their installation involves cutting a hole in the ceiling which creates a route for air to flow from the rooms into the roof space above. This airflow leads to a loss of useful heat and the movement of water vapour from the rooms into the roof space. The movement of water vapour can lead to condensation in the roof, particularly when the rooms below are wet areas such as bathrooms and shower rooms.

the fitting to allow for the safe dispersal of heat. Sealed downlighters are available which maintain the airtightness of the ceiling and these are particularly useful in wet rooms such as bathrooms and shower rooms. Dependent on their location, these may be required in order to meet electrical regulations. Where sealed downlighters are used it is still important to maintain the recommended air gap around and over the fitting so a hood, boxing or other suitable framing should be provided to support the roof insulation clear of the fitting.

Many downlighters are fitted with lamps which are designed to transmit much of the heat generated by the lamp out through the back of the lamp and lamp fitting. To avoid the lamp and fitting being damaged by overheating, the manufacturer’s installation instructions state a minimum air gap that should be provided around and over the fitting.

Where open downlighters are used, they should be installed with a suitable hood or boxing which completely encloses the fitting within the roof space. The hood or boxing should be sealed to the back of the ceiling to stop air leakage into the roof space. It is important that the hood or boxing is large enough to ensure the minimum air space is maintained around the fitting to allow for the safe dissipation of heat from the lamp. The hood or boxing should be made of materials that are not affected by heat from the enclosed lamp.

Correctly installed, downlighters should not create an air path between the rooms and roof space and should have the recommended air space around and above

Where roof insulation is installed at ceiling level it should be taken over any hood/boxing without gaps in the insulation to avoid cold bridging.

Action When installing downlighters ensure that the airtightness of the ceiling is maintained and that the manufacturer’s minimum recommended air gap is maintained around and above the fittings to avoid heat from the lamp causing a potential fire hazard.

roof insulation downlighter non-combustible material 75mm *

silicone sealant

plasterboard ceiling 100mm *

100mm *

silicone sealant

* or clearance as recommended by the fitting manufacturer

Section through downlighter and enclosure in a roof space

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STANDARDS EXTRA

Locks to individual flat entrance doors The locks to entrance doors of individual flats off communal stairways/corridors need on the one hand to provide good security and on the other not to hinder the occupants from leaving in the event of an emergency. These are conflicting requirements and there has been much debate on this topic as the industry tries to find the best solution. At present the guidance given in NHBC Standards 6.7 – D4 is generally considered to be the most appropriate means of satisfying these potentially conflicting requirements. Where the flat entrance doors are accessed from a communal stairway/corridor, the flat entrance door has to be a self-closing fire door. Being self-closing, the door will close behind anyone using the door and there is a risk of the lock self-latching and shutting the user out of the flat without a key. At best this can be annoying but it could be potentially more serious, for example, if the occupant exits the flat to seek assistance, leaving a child or elderly person in the flat. The guidance given in NHBC Standards says that locks should not be self-latching, thereby enabling the user to regain entry to the flat without the use of a key. This applies to flats on all floor levels, as the risk is the same regardless of the number of storeys. The guidance also says that the lock(s) should be openable from the inside by a single simple manual operation not requiring the use of a key. This ensures that no one should become locked-in in the event of a fire. There are various locks on the market, which can achieve the required locking arrangement. One option is to use a

1. Roller deadbolt rim latch

2. Morticed deadlock

‘roller deadbolt rim latch’ (1), which is face-fixed on the inside of the door. When unlocked it acts as a roller bolt, holding the door latched but it is still openable without the use of a key from both sides. When locked, the roller is thrown into the keep to act as a deadbolt - locking requires the use of a key on the outside when leaving the flat or turning the thumbturn on the inside of the door when the flat is occupied. Roller deadbolt rim latches on their own are unlikely to satisfy our guidance that the fixing, if burst open, should not pull out without breaking the door or its frame. To meet this guidance it is usually necessary to fit another lock to the door. Again, this lock should not be operable using a key from the inside - one such suitable lock is a morticed deadlock (2) with a key operation on the outside and a thumbturn inside. The two locks should be fitted, equally spaced on the closing edge of the door. Another option would be a morticed sash lock (3) with a pair of lever handles or knobs, with key locking outside and a thumbturn inside. In its unlocked position the door is held closed on the latch and can be opened by turning the handles/knobs. It can be locked and unlocked by a key on the outside or by the thumbturn on the inside. Action Ensure the locking arrangement to individual flat entrance doors off communal stairways/corridors cannot lock someone out without a key, can be opened from the inside without the use of a key and can resist someone trying to shoulder charge the door from the outside.

3. Morticed sash lock

Pictures courtesy of Yale.

STANDARDS EXTRA

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Flood risks Flooding is becoming a major issue in the United Kingdom and with increased development and the effects of climate change, the risk of flooding is likely to increase. Flooding is recognised as a material planning issue that should be considered jointly by planning authorities and the construction industry. For development to be sustainable, the construction industry must be able to assess flood risk and, where appropriate, identify measures to manage the risk. Development and flood risk planning guidance is set out in Planning Policy Guidance note 25 (PPG25) and the Scottish and Welsh equivalents (SPP7 & TAN15 respectively). However, the policy documents do not provide technical guidance on how flood risk should be assessed or what measures should be employed to reduce flood risks associated with development. This means that the practical application of the new planning guidance has presented a major challenge to developers and planners alike. In response to this challenge, CIRIA has published Development and flood risk – Guidance for the construction industry (C624), which includes information suitable for the non-expert (unfamiliar with flood risk issues) and more technical information suitable for use by practitioners conducting flood risk assessments. Prepared with support from NHBC, the guide is primarily intended to assist developers, builders, designers and planners, but will also be useful as background information for other parties involved in the development process, including insurers and mortgage lenders. The guide will also

help understanding of why flood related planning conditions might be imposed on new developments. The guide provides background information on the concepts of flood risk, different flood sources and the potential impact of development on flood risk. It recommends a tiered approach to flood risk assessment, which allows developers to anticipate issues early in the development process and design a development appropriately from the outset, thus minimising financial risk. The guide describes the roles of key parties in the planning process and outlines the responsibilities of the developer. For more information, or to be notified on release of the publication, contact CIRIA on 020 7549 3300 or visit www.ciriabooks.com.

Attic trussed rafters NHBC has been asked if ‘room in the roof’ attic trussed rafters can be cut, notched or drilled. Just like standard trussed rafters, attic trussed rafters should not be altered without the approval of the trussed rafter designer. However, drilling of the bottom member of the truss is permitted as follows: Maximum hole size Maximum hole diameter (mm)

147

16

172

20

197 or greater

25

Drilling is only permitted within areas shown (see bullet points)

400 300 300 300

300 300 300 400

Depth of bottom member (mm)

Drill on centre line of bottom member (holes no closer than 100mm)

Permitted drilling locations in bottom member

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STANDARDS EXTRA

Holes may be drilled only within areas shown in the diagram and if they are more than 500mm from a load-bearing support or more than 250mm from a plated splice joint. Holes must be drilled on the centre line of the member. There must be at least 100mm between holes. Maximum size of drilled holes is shown in the diagram. No other cutting, drilling or other alteration should be made to the trussed rafter. Action Where possible, ensure that services are routed in such a way that it is not necessary for them to pass through truss members. Only where it is absolutely necessary, should holes be drilled in the bottom member as indicated in the diagram.

Door limitation devices – flat entrance doors We have been asked if door limitation devices are required to be fitted to the entrance doors of individual flats. The purpose of the device is to allow the door to open sufficiently to enable the occupant to speak to the caller (e.g. a tradesman, meter reader, etc.) and see their identity card before letting them in. Entrance doors into the block of flats, (e.g. from the street), may be controlled by a door entry system but occupants cannot be certain that this will prevent unauthorised entry by persons who slip in behind a genuine resident or visitor. For this reason, door limitation devices are required to the entrance doors of individual flats. However in certain situations, where there is more control of persons who enter the building such as certain ‘wardencontrolled’ sheltered accommodation, it may be acceptable for door limitation devices to be omitted.

Action Door limitation devices should be provided to all flat entrance doors. Discuss any proposal to omit them with NHBC.

Buildingfortomorrow 2005 Are you prepared? Our Building for tomorrow seminars provide the latest information on some of the principal topics in house building and help you plan for the future. We keep you up-to-date on recent changes to Building Regulations, Government initiatives and planning, NHBC Standards and inspection, as well as a variety of topical issues such as the current focus on customer service. Building for tomorrow combines industry experts with NHBC practitioners to provide you with the right level of information, on the issues that make a difference to you.

Who should attend Building for tomorrow is aimed at anyone for whom keeping up-to-date on industry issues and company performance is important, as well as those responsible for compliance with technical standards.

Learning styles and exhibition

Venues

Date

Cambridge Belfry, Cambourne Motor Cycle Museum, Birmingham Nr NEC Village Hotel, Nottingham Vauxhall Recreational Centre, Luton Blue Mountain Golf Centre, Binfield, Berks Ramada Hotel, Maidstone Redworth Hall, Co Durham Cedar Court Hotel, Wakefield Reebok Stadium, Bolton Marriott Hotel, Portsmouth Marriott City Centre Hotel, Bristol Village Hotel, Cardiff

15 Feb 16 Feb 17 Feb 21 Feb 22 Feb 23 Feb 1 March 2 March 3 March 8 March 9 March 10 March

Seminars are based around talks or interactive presentations, with plenty of opportunities for questions and discussion with speakers.

Cost The cost per delegate is £115 + VAT (£135.12), which includes a buffet lunch and refreshments.

Programme Topics for the day include: - Homes for £60,000? – The Planning and Compulsory Purchase Act - Closing in on claims - Stop press – last minute updated issues - Standards Extra – new NHBC Standards - Building out defects through inspection - Robust Details Ltd – the latest position - Building Regulations – Approved Documents A, C & P. - New home customer satisfaction survey

Separate events will be held in Scotland and Northern Ireland on 16 March, with topics tailored to specific issues in these areas. For more information please contact for Scotland Helen McCallum on 0131 313 1001, and for Northern Ireland Nicola Thompson on 028 9038 6005. To book or request more information on seminars in England and Wales please contact Nicky Clements on 01908 223780.

STANDARDS EXTRA

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Building Regulations in England and Wales – Approved Documents A, C and P Part P – Electrical safety From 1 January 2005 all electrical work in new dwellings will need to comply with the new Part P requirements and be carried out by competent persons. Evidence of compliance with Part P will be that the work has been carried out by a competent person and the provision, to the building control body, of a BS 7671 ‘Requirements for electrical installations’ certificate for the installation. Competent persons must be a member of a competent person self-certification scheme and the Government has approved five such schemes. You will need to make sure that your electrical contractor is a member of a scheme.

Part A – Structure The new edition of Part A came into force on 1 December 2004. The main changes to Part A are: Requirement A3 (disproportionate collapse) has been extended to apply to all buildings irrespective of height, where previously it applied to buildings of five or more storeys. For flats of masonry construction up to four storeys this means providing effective horizontal ties or effective anchorage of floors to walls. This new criterion can be achieved by slabs bearing onto walls or by use of straps. Roof-space accommodation is now counted as a storey for determining Building Class for Requirement A3. Cavity wall ties should now be of stainless steel regardless of the location of the building and whether full/partial insulation is proposed. Updated guidance on domestic garages to reflect modern practice is now included. Transfer of span tables to a new TRADA publication ‘Span tables for solid timber members in floors, ceilings and roofs (excluding trussed rafter roofs) for dwellings’. Improved guidance on re-covering of roofs is included.

Part C - Site preparation and resistance to contaminants and moisture The main changes to Part C which also came into effect from 1 December 2004 are: The guidance on contamination is now extended to “land associated with the building” rather than land covered by the building. The guidance on contamination and precautions against radon now also applies to conversions. The guidance deals with all aspects of dampness in buildings including decay in wood floors caused by leaks from appliances. In order to bring all precautions against

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STANDARDS EXTRA

condensation and dampness together, former requirement F2 ‘Condensation in roofs’ has been moved to Part C. More guidance on aspects of climate change such as flooding, resistance to driving rain and thermal movement is now included. A 75mm residual cavity is now called for in areas of very severe exposure where partial cavity fill is used and the outer leaf is of fairfaced masonry. Action Ensure that you are familiar with the new and revised Approved Documents - in particular the increased width of residual cavity now called for if you build in areas of very severe exposure and the universal requirement for stainless steel wall ties.

New changes that affect EcoHomes scoring EcoHomes is the environmental assessment method run by the Building Research Establishment (BRE) for new and newly converted housing developments. Developments can achieve a rating of ‘Pass’, ‘Good’, ‘Very Good’ or ‘Excellent’, but achieving the desired score may become more difficult with the issue of the latest version EcoHomes 2005. The main drivers for EcoHomes are English Partnerships, social housing sites (either in their own right or under Section 106 agreements) receiving Housing Corporation funding and also a growing number of planning authorities. EcoHomes 2005 will apply to all sites registered with BRE by your EcoHomes assessor after 15 November 2004. There are seven major categories that EcoHomes considers: Energy, Transport, Pollution, Materials, Water, Land Use and Ecology, and Health and Well Being. Within these seven categories are 27 issues and many of these remain broadly unchanged in EcoHomes 2005 except for some relatively minor amendments to the wording in the guidance. However, there are several areas where alterations have been made which will make a difference to the scoring. Some of the more easily attained credits have been removed. A new issue 'Zero Emission Energy Source' has been added which introduces credits and rewards the use of renewables, such as timber, for the

first time. Additional timber certification bodies are now recognised and these are: CSA –

Canadian Standards Association

MTCC – Malaysian Timber Certification Council SFI –

Sustainable Forestry Initiative

FSC –

Forest Stewardship Council Certification Scheme

PEFC – Programme for the Endorsement of Forestry Certification. Significant changes have also been made to credits awarded for good public transport links and for the first time EcoHomes differentiates between rural and urban locations in relation to public transport. However, the requirements for urban transport are more stringent than previously and this may have an adverse impact on scoring. As well as having a large team of EcoHomes assessors, NHBC also provides training which covers the changes contained in EcoHomes 2005. This training can be tailored to your individual requirements and offers practical advice to give you a thorough understanding of the EcoHomes assessment process. It also provides you with the knowledge and skills necessary to achieve the best possible EcoHomes scores for your developments.

For further information on either the new guidance, or EcoHomes training, please contact NHBC on 0870 241 4310.

Air Admittance Valves(AAVs) AAVs are commonly used in above ground foul drainage systems. As the name suggests they are one-way valves which are capable of allowing air into the drainage system. They do not permit foul air from the drainage system to escape, which is why they can be situated within the dwelling. For aesthetic reasons AAVs and associated pipework is usually boxed in. In Standards Extra 27 (August 2003) we highlighted the need to ventilate this boxing to provide adequate air supply to the AAVs. However, the third party assessments and manufacturers’ installation details for AAVs also say the valves should be

accessible for periodic inspection and maintenance. To satisfy this requirement the AAV should be fitted behind an access panel that can be removed for inspection and maintenance of the valve. Action When boxing in AAVs, ensure that there is an adequate air supply to enable the valve to work properly and suitable access for periodic inspection and maintenance of the valve.

STANDARDS EXTRA

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Questions & Answers Below is the answer to a question we have recently been asked in NHBC Technical.

Handrail to staircases - tapered treads/winders Question Where stairs have tapered treads/winders, is a handrail required to the outside of the stairs?

Considerations ■ A safe handhold is required for the full rise of any stairs with a total rise greater than 600 mm. ■ A suitable newel post can provide a safe handhold.

Answer Single newel In England, Wales and Scotland where the stairs have between one and four tapered treads/winders and the newel provides a safe handhold, a handrail is not required to the outside of the stairs.

Additional Handrail not needed

Additional Handrail not needed

Additional Handrail not needed

Additional Handrail needed

In Northern Ireland a handrail should be fitted to the outside of the stairs (required by building regulations). Double newels In England, Wales and Scotland where the newels provide a safe handhold, a handrail is not required to the outside of the stairs.

Additional Handrail not needed

Additional Handrail not needed

In Northern Ireland a handrail should be fitted to the outside of the stairs (required by building regulations). In all cases where a handrail is needed to the outside of the stairs, it should be continuous for the whole rise to avoid the need to change hands.

NHBC Technical Buildmark House, Chiltern Avenue, Amersham, Bucks HP6 5AP Tel: 01494 735859 Fax: 01494 735717 Email: [email protected] www.nhbc.co.uk 8

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