Standards Extra 42 - September 2008 - NHBC · PDF file32mm HepVo (BV1) must be Vertical ......

B215 Standards Extra 42 v3 29/8/08 15:11

NHBC’s technical newsletter

Extra

This edition includes: Discharges from unvented hot water storage systems

Guidance when building homes alongside existing buildings

Sustainability Extra – Issue 02

Revised NHBC Standards for September 2008

Standards

September 2008

42


300mm

between pipe clips

Standards Extra

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2 Discharge your responsibilities correctly

3 Building homes alongside existing buildings

4 Questions and answers

NHBC Standards 2008

Discharge your responsibilities correctly Discharge pipes from unvented hot water storage

v

Discharge Pipe

Visible point of discharge

Pipe adapter BV21

Soil Stack

30

0 M

inim

um

Straight adapter BV3

32mm HepVo (BV1) must be Vertical and adjacent to the water unit, to be visible and easily accessible.

Waste typically discharged to soil stack through boss adapter

Waste alternatively discharged through soil manifold

Independent 32mm Polypropylene discharge pipe to BS 5254 or BS EN1451 Pipe run to the soil stack connection to be supported with pipe clips.

Connecting a discharge pipe to a soil stack

systems (UVHWSS) are controlled by Building Regulations which currently show the discharge taken to a gully outside of the building. It is also possible to discharge them to a soil and vent pipe in conjunction with a waterless HepVo valve.

However, there are a few golden rules in doing this and NHBC inspectors often find things on site have to be altered where the installation is incorrect:

■ Read the fitting instructions for the HepVo valve. It must be used in the vertical position for discharge pipes. This is confirmed in BRE certificate for the valve (certificate number 042/97) and BRE Information Paper IP8/07 on self-sealing waste valves.

■ To cope with the high discharge temperatures pipework must be in copper or polypropylene. Other plastic plumbing can tend to soften and distort at such temperatures. As polypropylene pipe cannot be jointed by solvent weld it is easy to identify. Failing that the pipes are marked at regular intervals with BS 5254 or BS EN 1451.

■ Discharge pipework must not be used for other purposes. Don’t be tempted to connect sink wastes, washing machine wastes or condensate pipes to the discharge pipe. This is to ensure the pipe never becomes blocked.

■ After the tundish there must be a minimum 300mm vertical drop before the first bend. The HepVo valve should be installed in the section between the tundish and the first bend.

■ The polypropylene pipe must have a continuous fall and be properly supported, so that it doesn’t sag between supports. Supports should be at a maximum 300mm centres.

■ By taking the discharge pipe to a soil and vent pipe the only place that the homeowner can see the discharge will be at the tundish. This must be visible. Some UVHWSS have the tundish within the boiler/cylinder casing and it may be necessary to reposition the tundish so as to make it visible or cut a neat hole in the casing.

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If your plumbers are going to take discharge pipes to a soil and vent pipe then ensure they know how to do it properly using the right materials. Alterations at a later stage in the construction can be difficult and disruptive. A

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Issue 42 September 2008

Building homes alongside existing buildings Standards Extra 25, published in December 2002, included some general guidance on what NHBC would require from the builder when submitting an application for warranty cover on a new home to be built alongside an existing building.

The rationale of the previous article is unchanged in that the ongoing scarcity of building sites in built-up areas results in more homes being built alongside existing buildings. Standards and Technical continue to receive a number of enquiries about this subject and therefore it is probably a good time to revisit the matter to reinforce our requirements and expand the guidance provided in the earlier article.

The primary consideration for NHBC is to make sure that the new home is constructed so that it can remain as a functioning, waterproof, and separate entity for the

duration of its minimum 60-year anticipated design life.

New build warranty will be offered where the new home is designed as an independent structure, with a new foundation and wall built alongside the existing. A qualified engineer with suitable knowledge and experience should design the new foundation and wall.

Acceptance is based upon the following considerations: ■ The existing foundation and wall may not be

structurally sound. ■ Poor detailing such as founding the new building at the

wrong level could result in load transfer from one building to another, for which it may not have been designed.

■ Where the two buildings are not structurally independent there is a risk of differential movement and associated damage.

■ The existing wall may not provide satisfactory in-service performance, particularly in respect of weatherproofing, damp-proofing, sound and fire.

■ Excluding the existing foundation and wall from

new build warranty cover would not provide satisfactory

protection to the homebuyer.

New build warranty cover may also be offered where the

existing foundation and wall are incorporated into the

design of the new home, but only where a qualified engineer

with suitable knowledge and experience is engaged to carry

out the design. The rationale for not providing a new

foundation and wall should also be justified by the engineer.

In these circumstances NHBC will offer new build warranty

cover only where the following issues have been fully resolved:

■ The existing foundation / supporting ground and wall

must be investigated to ensure they are suitable to be

incorporated in the design of the new home.

■ An effective dpc must be present in the existing wall

and be linked to the dpc and dpm in the new home.

■ The interface between the new and existing walls and

roofs must provide a weatherproof construction.

■ The interface between the new home and the existing

building must provide suitable allowance for the effects

of differential movement.

■ Confirmation is required that the Building Control Body

has accepted the existing wall as complying with the

relevant parts of the Building Regulations.

■ It must be made clear to the owners of the new home and

the existing building, that the existing wall is to become a

party wall. This should be done by a Party Wall Agreement

in accordance with the Party Wall Act 1996. NHBC will

require proof that this matter has been resolved.

The alternative use of Conversion warranty cover is

normally restricted to projects where the build forms part

of an overall conversion project.

For builders intending to build a new home alongside an existing building, consider the above criteria and consult with NHBC as soon as possible. A

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New build alongside existing

Existing foundation and wall

New foundation and wall

Compressible material

Typical detail of new foundation and wall

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Standards Extra

QU

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Rendering on timber framed walls Should timber battens, used to support external render lathing, be protected with a strip of dpc material placed between the batten and lathing?

A ■ Cement render may be porous and allow

wetting of the supporting battens if dpc protection is not provided and this could cause decay.

■ The TRADA timber frame construction handbook shows a strip of a dpc between the face of the timber batten and the cement render.

■ Yes, timber battens used to support render lathing should be isolated from a cement render with a strip of dpc. The dpc material should be a minimum 500-micron polythene and extend beyond the outer edges of the batten. Where horizontal battens are provided e.g. around openings or as cavity barriers, the dpc should extend across the top face of the batten and be dressed up under the breather membrane (see diagram opposite).

Registered builders are reminded that the 2008 Standards became effective on 1 September. All homes whose foundations are concreted on or after that date must meet with them.

This year’s major change was to Chapter 6.2 ‘External timber framed walls’. Changes to other Chapters are identified by the text being underlined and a vertical marker adjacent to the paragraph.

In addition to registered builders being aware of the new Standards it is equally important for consultants, subcontractors and other professionals to be made aware of the changes. If they are working for you then, for example, Architects and Consulting Engineers need to

know what changes have been made to Chapter 6.2 regarding movement of the timber frame.

NHBC operate a ‘Professional Database’ to cover this situation. Having purchased an initial copy of the Standards professionals will be added to our database and will receive notification when a new updated copy of NHBC Standards is released. In addition they will also receive copies of our Standards Extra newsletter throughout the year.

If you would like to purchase a copy of NHBC Standards and subsequently be added to our professional database please contact NHBC sales on 01494 735328 or log on to our website at www.nhbcbuilder.co.uk and place your order.

Standards A4 hard copy version including a free CD Rom £70.00 zero VAT (HB 1286)

Standards CD Rom only £47.00 Inc VAT (HB 1285)

In addition a handling / P&P charge is applicable of £4.70 Inc VAT

NHBC Standards 2008

NHBC Standards 2008 edition

timber frame

treated timber battens

breather membrane

DPC - extended beyond edges of battens

sheathing

cavity barrier batten

DPC - dressed up underbreather membrance

cavity

metal lathing (with orwithout paper backing)

cement render

NHBC Standards and Technical

NHBC House, Davy Avenue, Knowlhill, Milton Keynes, Bucks, MK5 8FP Tel: 0844 633 1000 Fax: 0844 633 0022 www.nhbcbuilder.co.uk Email: [email protected]

4 HB2451 09/08

mailto:[email protected]

B214 Sustainability 2 v3 16/9/08 20:26 Page 3

2 Sustainability

Extra September 2008

Zero carbon: what does it mean? In December 2006, the Government signalled its intention for new housing in England and Wales to become ‘zero carbon’ by 2016. It defined the ‘zero carbon’ home as: ‘one that delivers zero carbon (net over the year) for all energy use in the home – cooking, washing and electronic entertainment appliances as well as space heating, cooling, ventilation, lighting and hot water’.

(Building a Greener Future: Towards Zero Carbon Development, CLG December 2006)

Oxley Park, Milton Keynes

It means that any energy used over the course of the year needs to be compensated for by energy generated by renewable means, such as solar thermal panels, solar electric panels, wind turbines, biomass boilers, etc.

‘Merton Rule’ planning requirements (where a percentage of the energy used on a development has to be provided by renewables) are increasingly being used by local authorities to hasten progress towards this target. Also homes which are government funded or built on English Partnerships land already have to comply with standards better than Building Regulations. Similar targets will be adopted in Scotland and Northern Ireland where similar planning intervention is also occurring.

The shift towards zero carbon homes will have significant impacts on the way in which homes are designed, constructed, serviced and maintained and so there will be implications for all concerned, including homeowners, house builders and NHBC.

How will zero carbon homes be achieved? Zero carbon is a massive leap for the house-building industry as it represents an improvement on present energy standards of about 150%. Homes will need excellent levels of fabric insulation to the walls, roofs and floors and the best available windows and doors. The as-built construction will need to be very airtight and so a mechanical ventilation system with heat recovery will probably be required.

But this combination of fabric insulation, airtightness and ventilation measures is only likely to achieve a maximum improvement of up to 40% – far short of the 150% improvement needed. The gap will need to be made up with renewable energy generation and the following technologies may be appropriate:

� Solar thermal (solar water heating) � Solar electric (photovoltaic) � Wind turbines � Biomass boiler or stove (normally burning logs,

wood chips or pellets).

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Sustainability Extra

Great Bow Yard, Somerset

The suitability of a given technology will depend on the type of homes and their location. Solar panels may be well suited to a single home with a large south-facing roof, but they would be less well suited to an apartment block with a relatively small roof area or a north-facing roof. Similarly wind turbines are best located in windy locations, away from wind-spoiling features such as buildings and trees. Because biomass systems require significant space for fuel storage and some regular attention, they may be best suited to ‘managed’ apartment blocks.

‘NHBC Guide to Renewable Energy’ gives further information on renewable energy technologies and is available at www.NHBCBuilder.co.uk (see ‘publication download’).

Energy efficiency Few would argue with the principle of further reducing energy consumption and CO2 emissions from new homes as the homes built today will still be in use in many decades’, even centuries’ time. For that reason, good insulation and attention to airtightness will continue to deliver benefits over a very long period.

NHBC firmly supports the Government’s overall objective of minimising CO2 emissions from housing and recognises the benefits to homeowners and occupiers, particularly in the current climate of rapidly rising fuel prices. We do, however, need to ensure that changes to construction and services work as intended and deliver their expected benefits without causing problems for homeowners.

NHBC is committed to ensuring that homeowners’ interests are fully considered in the zero carbon debate and protected. Some examples of the various technologies we have seen have not inspired confidence and we’re anxious that homeowners should not be used as ‘guinea

pigs’ and experimented on with under-developed products and systems.

Renewable energy generation As already mentioned, renewable energy generation will be required to make up the gap between the ‘up to 40%’ that can be dealt with by changes to the construction and services and the required 150% overall improvement needed. The main issue is whether that energy has to be generated on site (on the individual plot or within the development site) or whether offsite generation is acceptable.

It seems sensible for all possibilities for producing energy on site to be explored and for those which are practical and reasonably cost-effective to be adopted. As mentioned above, the possibilities will depend on the type of homes and the type and location of the development and for some developments, notably apartment blocks on urban infill sites, there will be a severely limited scope for on-site energy generation. A requirement for generation of all energy on site would effectively prevent housing from being developed on many sites.

Figures presented in ‘Final Regulatory Impact Assessment: Building a Greener Future’, CLG July 2007 (available from www.communities.gov.uk) present a compelling case for flexibility in allowing offsite generation. They suggest that the amount of CO2 emissions saved per pound spent is significantly increased if offsite generation is used.

UK-GBC definition of zero carbon In May this year the UK Green Building Council published the ‘Zero Carbon Task Group Report – The Definition of Zero Carbon’ (available from www.ukgbc.org). The report recommends that all new homes should be built to achieve strict energy efficiency standards and that, where >>>

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>>> possible, renewable energy should be provided on site or from nearby solutions. It does suggest, however, that in certain circumstances renewable energy generation off site should be allowable or, alternatively, a payment could be made to a ‘Community Energy Fund’, which would be used to fund community-scale solutions.

NHBC welcomes the UK-GBC report and regards its proposed definition of zero carbon as well considered and logical. We are expecting that a government consultation on the definition of zero carbon, based on the UK-GBC report, will be announced during the autumn. This will provide an opportunity for the house-building industry to provide input to this important debate.

Solar electric (photovoltaic) panels

Compensating improvements to the stock of existing homes NHBC’s response to the anticipated government consultation is likely to suggest that ‘compensating improvements’ should provide a way for house builders to satisfy the requirement for zero carbon homes. We believe that, provided homes are built to a high standard of energy efficiency (reflecting the fact that the fabric will be performing over many decades/centuries), the focus should be on achieving the maximum reduction in CO2 emissions per pound spent.

Beyond the investment in the fabric, we consider that it may be preferable for house builders not to be required to invest in renewable energy technology (beyond those which are practical and reasonably cost-effective). Instead they should be allowed to fund improvements to the existing stock.

In this way, we would be achieving a ‘triple win’:

Win 1 Every new home achieves excellent energy

performance through fabric improvements,

delivering benefits for the entire lifetime.

Win 2 The energy efficiency potential of the stock

of existing homes – a far greater problem –

is unlocked.

Win 3 Greater CO2 savings are made at a reduced

cost to the industry.

The Barratt Green House The latest example of a home designed to achieve zero carbon performance is the Barratt Green House, which was officially opened on 15 May 2008. Built on the Innovation Park at the Building Research Establishment in Watford, the Barratt Green House was designed by architects Gaunt Francis and built by Barratt Developments plc. It was the winning design in a competition run by the Mail on Sunday, supported by NHBC and the National Centre for Excellence in Housing. >>>

Barratt Green House (copyright Denis Jones)

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Barratt Green House interior (copyright Denis Jones)

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Scoring almost 92 credits out of a maximum of 100, the home meets Level 6, the highest level of the Code for Sustainable Homes. Lessons learnt during the design and construction will be useful for Barratt as they roll out homes at higher levels of the Code into their general output over forthcoming years.

The Barratt Green House is expected to remain on the Innovation Park for a two-year period, during which its performance will be evaluated.

The experiences gained through designing, building and evaluating its performance will be invaluable as we make progress towards the zero carbon and higher Code level homes of the future.

Further information on the Barratt Green House is available from the National Centre for Excellence in Housing website: www.homein.org

Further information on the BRE Innovation Park can be found on the BRE website at www.bre.co.uk

How does the Barratt Green House achieve Zero Carbon?

Energy efficiency The home achieves zero carbon performance using a carefully balanced combination of fabric, mechanical and electrical features:

Fabric � The floors, walls, and roofs achieve U-values of 0.11W/m2K or lower. The external walls,

constructed using aircrete panels, are externally insulated with 180mm of insulation to minimise thermal bridging.

� U-values for windows and doors are 0.68W/m2K (triple-pane) to 1.40W/m2K (double-pane).

� Airtightness – an exceptionally low figure of 1.0 m3/hm2 was achieved by close attention to detailing and workmanship.

Mechanical � A mechanical ventilation system provides fresh air to habitable rooms. A heat

recovery system takes the heat from the outgoing exhaust air and transfers it to the incoming ventilation air in order to provide most of the home’s space heating.

� 3.3m2 of solar thermal collectors are used to provide most of the home’s hot water heating.

� Heat back up is provided by means of an air-source heat pump.

Electrical � 4.1 kW of roof mounted solar electric (photovoltaic) panels and 3.4 kW of

ground-mounted panels, installed near to the house, are provided.

� All of the lighting throughout the house uses low energy or LED (light emitting diode) bulbs.

� A building management system controls heating, lighting, and automatic window shutters to minimise summer overheating.

Water conservation Total water consumption has � Low flow taps and shower heads and low flush WCs. been minimised to 80 litres per

� A rainwater harvesting system that recycles rainwater collected from the roof person per day (average UK and paving around the house, which is then used for WC flushing and laundry. usage is 150 litres) by the use of:

Materials � All timber was FSC (Forest Stewardship Council) certified.

15 out of the available 24 Code � Other materials obtained from companies with Environmental Management points were scored here: Systems in place.

Other features � Good daylighting throughout improves ‘health and well being’ and reduces energy The many other features of used for lighting.

the house include: � ‘Lifetime Homes’ criteria have been met including the provision of a downstairs WC that can be upgraded to accommodate a shower.

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NHBC Foundation

NHBC Foundation calls for research proposals The NHBC Foundation (NHBC’s independent research institution) recently agreed its research priorities for the next twelve months. The Foundation’s research will continue to support NHBC’s purpose of ‘raising the standard of new homes and providing consumer protection for new home buyers’ and focus on three themes:

� ‘Zero carbon’ Projects in this area will be geared towards assisting the house-building industry in achieving targets to reduce CO2 emissions to satisfy Building Regulations and the Code for Sustainable Homes. Our work will mesh with that of the newly-formed Zero Carbon Hub (see below).

� ‘The homeowner’ Projects under this heading are likely to centre on ensuring that the consumer’s interests are not overlooked during the transition towards zero carbon homes. We are also expecting that initiatives such as the Office of Fair Trading study into house building may generate research work.

� ‘Risk management’ Past UK and more recent international experience suggests that small changes to housing construction can have profound effects on the performance of homes. Projects in this research area will be aimed at ensuring that future generations of homes are buildable, perform well in use, meet reasonable expectations and do not repeat past problems.

If you have a suggestion for research that would be particularly useful for the industry, do let us know. Please contact Neil Smith (Group Research & Innovation Manager) at [email protected].

Further information on the NHBC Foundation and all of the reports published to date are available at www.NHBCFoundation.org

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The Zero Carbon Hub Working towards Zero carbon The Zero Carbon Hub was launched in July and is taking a lead on day-to-day operational responsibility for delivering low and zero carbon new homes. The Callcutt Review identified the need for this new private/public partnership organisation which will monitor, co-ordinate and guide the zero carbon programme. The Hub provides a direct conduit to the 2016 Taskforce, consisting of three government ministers and senior leaders from the private, public and NGO sectors.

A small Board led by Chairman Paul King of the UK Green Building Council oversees the Hub’s operation. Neil Jefferson of NHBC has been appointed Interim Chief Executive and NHBC is providing financial and operational support to the Hub.

The Hub is engaging organisations active in low and zero carbon homes in various workstreams, including energy efficiency, energy supply, examples and scale-up, consumer engagement and skills and training.

If you would like further information about the Zero Carbon Hub,

contact Neil Jefferson at [email protected]. Neil Jefferson

mailto:[email protected]


Sustainability Extra

Code for Sustainable Homes: Technical Guide – addendum published Communities and Local Government (CLG) published a statement and addendum to the Technical Guide in June.

The changes clarify that:

� There is no change from the October 2007 Technical Guide in the way that air source heat pumps can be used.

� There is currently no requirement in the Code to justify the choice of fuel.

The statement also says:

“Some stakeholders have expressed concern that the Code Technical Guide as currently drafted (and amended by this addendum) may lead to developers choosing heating and hot water solutions that do not result in the intended reduction in carbon emissions and fuel bills, particularly at Code levels 3 and 4.

The Department is currently looking into this and, based on those investigations, will determine what actions (if any) are required to address this issue in advance of consultations on revisions to Part L of the Building Regulations and the Code (both planned for early 2009)”.

Further information is available from the Planning Portal website at www.planningportal.gov.uk

Concrete Centre publishes ‘Energy and CO2: Achieving targets with concrete and masonry’ This recently published guide will assist designers and builders in meeting the mandatory energy and CO2 targets for levels 3 to 6 of the Code for Sustainable Homes. Amongst the information provided is guidance on addressing airtightness and thermal bridging. Also a variety of ‘Code solutions for external walls’ are presented – some of the solutions achieve U-values down to 0.15W/m2K.

This guide can be downloaded at www.concretecentre.com (see ‘Publications Library’).

Energy Saving Trust Guidance published ‘Energy efficiency and the Code for Sustainable Homes’

The Energy Saving trust (EST) has published two further guides advising on how to achieve energy efficiency to comply with Levels 4, 5 and 6 of the Code. They supplement earlier guidance on achieving Level 3. Although the guidance comes with certain ‘health warnings’, it does usefully demonstrate packages of measures that can be used at each level.

The guides are available from the ‘housing and buildings’ section of the EST website at www.est.org.uk’.

Energy Saving Trust publications

Concrete Centre publication

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HB2450 09/08

Standards Extra 42 - September 2008 - NHBC · PDF file32mm HepVo (BV1) must be Vertical ......

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Transcript of Standards Extra 42 - September 2008 - NHBC · PDF file32mm HepVo (BV1) must be Vertical ......