NHBC’s technical newsletter
Standards
Extra
May 2008
This edition includes:
Revised Chapter on
timber frame construction
Air leakage testing and EPCs
New guidance on radon
Sustainability News – Issue 01
Stop press
– Access to gas flues revisited
41
2
2008 Standards
distribution
Electrical
requirements
change – new BS 7671
3
Revised Chapter
on timber frame
construction
4
Air leakage testing
and EPCs
5
Sustainability
6
Fire safety survey –
lessons to be learnt
2008 Standards
distribution
In the interests of reducing the environmental
impact and print and distribution costs, NHBC has
reviewed the quantity of hard copies of the 2008
Standards that are distributed to registered builders.
The quantity each builder receives free of charge
is now based on the number of plots registered with
NHBC in the previous calendar year. This means that
all builders who were inactive in 2007 will only
receive a CD-ROM version of 2008 Standards.
If an inactive builder subsequently registers plots, a
hard copy will automatically be despatched to them.
All registered builders will continue to receive
Standards Extra.
Electrical requirements
change – new BS 7671
7
New guidance
on radon
Although electrical contractors should
know that a new version of BS 7671,
the wiring regulations, was published
in January, it is worth checking this
with them.
8
Questions and
answers
The new standard becomes effective
from 1 July 2008. Installations designed
after that date must comply with the
new standards.
Stop press
– Access to gas
flues revisited
There are a number of major changes
in the new standard. The changes are
about protecting people from electric
shock by improving the safety of
electrical installations. There may be
cost implications in meeting the new
requirements of BS 7671 compared
with the previous edition.
The main changes are:
protected by an RCD, unless the
cables have an earthed metallic
covering or mechanical protection
from nails, screws, etc
Cables in ‘safe zones’ which are
installed at a depth of less than
50mm will require RCD protection
Any cable (irrespective of the
depth) within a partition which has
metallic parts (excluding fixings)
must be protected by an RCD
Zones for electrical installations
near to baths and showers
have changed
BS 7671 now contains
requirements for photovoltaic
(PV) power supply systems.
All socket outlets in homes
(with minor exceptions) must
be protected by an RCD
Concealed cables (lighting and
power) which are installed at a
depth of less than 50mm must be
2
ACTION
CONTENTS
Standards
Extra
Ensure that your electrical
contractor is fully aware of the
changes to BS 7671 and that
he will be meeting with the
requirements later in the year.
Issue 41
May 2008
Revised Chapter on timber frame construction
The current version of Chapter 6.2 has
its origins in the mid-1980’s when timber
frame was being build to three storeys
only. Today it can go to seven storeys
and the new Chapter recognises this.
The review of Chapter 6.2 has looked at
all aspects of timber frame construction,
some of which fall outside the remit of
Chapter 6.2. However, those issues which
do fall outside the remit will be covered
in a guide to be published by the UK
Timber Frame Association. They include
issues such as the effect of differential
movement on internal plumbing and
situations when a new timber framed
extension is added to an existing building.
So what are the main changes
in Chapter 6.2:
Preservative treatment of studs
Softwood studs currently require
preservative treatment and this has
been continued in the new Chapter.
Where I-joists are used as studs in
timber framed construction they
will also require treatment and
currently NHBC is talking to the
joist/stud manufacturers and the
preservative treatment industry
on how best to achieve this.
Differential movement
As the timber frame dries it shrinks
and results in differential movement
between the timber frame and the
Table of differential movement
“rigid” parts of the construction,
such as the outer leaf of masonry.
This differential movement needs
to be taken into account by both
designers and those on site. Unlike the
old version of Chapter 6.2 the new
one has a table of likely movement
dimensions for buildings up to seven
storeys. It is vital that the dimensions
are followed otherwise damage may
occur to the structure and finishes.
Chipboard as a sheathing material
Chipboard, type P5 or P7, to BS EN
312 will in future be accepted as a
sheathing material.
Insulation materials
There has been a long established
NHBC requirement for insulation in
walls of timber frame construction
to be “breathable”. However, these
materials are not as thermally
efficient as some rigid board
insulants, but these board products
don’t breathe. In future where these
materials are used they will require
a third party assessment specifically
for that use. They also need to be
well fitted so that there are no gaps
between the insulation and the
timber frame studs. If there are
gaps they may cause cold bridging
and condensation may occur.
Excessive gaps will have to be
foamed-in using expansive foam.
Cavities
Today cladding comes in a variety of
types from masonry to curtain walling.
The Chapter has a table to indicate
suitable cavity widths and there is
also a cross reference to Chapter
6.9 ‘Curtain walling and cladding’.
It’s also worth confirming that we
require a cavity in all situations and
direct application is not accepted.
Sole Plates
Packing of sole plates may be
necessary depending on how level
the substructure is. The packing should
not exceed 20mm and the chapter
shows three acceptable ways of
doing this. Packing of gaps exceeding
20mm must be designed by the
timber frame manufacturer’s engineer.
Proximity of lowest timber
to ground level
Ideally the lowest timber, perhaps the
sole plate, should be 150mm higher
than ground level. However, floor
levels are getting closer to ground
level and in exceptional circumstances
it may be reduced to 75mm.
Certification
In future the certification procedures
in England and Wales, Scotland and
Northern Ireland will be universal.
NHBC will shortly be in contact with
timber frame certifiers to explain
the new procedures.
ACTION
A revised version of Chapter 6.2
‘External timber framed walls’
is included in the 2008 Standards.
If you are building timber
frame or are thinking of
doing so make sure you are
aware of the new Chapter
which will be operative
from 1 September 2008.
Permanent structural packing
under sole plate
3
Standards
Extra
Air leakage testing and EPCs
NHBC’s UKAS accredited Air Leakage Testing Service
is celebrating a successful first full year of operation.
such buildings despite the 2006
Building Regulation enhancements for
purge and trickle vents. Whole house
ventilation systems are becoming
more widely used and should prevent
condensation and mould issues
where incidental natural ventilation
is inadequate.
In this article we look at what we have
learned from a sample of recent tests
and the legislative drivers.
parge coat behind the dry lining to
achieve permeability rates of below
5 m3/(h.m2) at 50 Pa.
It is pleasing to note that most tests have
been successful. Typically construction
teams use their first plots as a
benchmark then continue to learn and
improve the performance of their homes.
Since 6 April 2008, HIPs and EPCs are
required for all new build dwellings.
Social housing and some planning
authorities are setting stringent targets,
(typically Code Level 3), whilst all HIPs
from 1 May 2008 require a Code rating.
The current regulatory standard of
10 m3/(h.m2) at 50 Pa has been achieved
first time in over 95% of the homes we
have tested. Many designers now adopt
holistic approaches and apply tighter
air leakage standards to optimise fabric
insulation or heating systems. Flats for
example can still use electric heating
if the air leakage rate is 7 m3/(h.m2)
at 50 Pa or better. Partial cavity wall
insulation is still possible with air
leakage standards of 8 m3/(h.m2)
at 50 Pa or less.
Timber frame with its vapour control
layer and other board materials
performs well with typical air leakage
rates of between 4 and 7 m3/(h.m2) at
50 Pa. Wet plastered masonry can be
slightly better. Dry lining on masonry is
typically between 7 and 9. It is essential
to install the perimeter plaster sealing
beads behind dry lining, or permeability
can be as high as 16 m3/(h.m2) at 50 Pa.
Some builders extend their acoustic
4
The Code for Sustainable Homes has
been developed for two purposes,
firstly to offer an independently
accredited, Government endorsed
sustainability rating, which will identify
“green” homes. Secondly, the Code is
an indication of the direction of future
Building Regulations. Level 3 (25%
improvement over current 2006
Building Regulations) is the proposed
standard for Part L1a in England and
Wales by 2010.
There are options to trade thermal
insulation, heating systems, air
permeability and renewable energy
sources. However, improvement to air
leakage will often be the most cost
effective approach. For level 3 the
optimal air leakage target is 3 m3/(h.m2)
at 50 Pa. Evidence already suggests
that condensation may be an issue in
The future holds the Government
promise of no Stamp Duty for zero
carbon homes (Level 6 Code for
Sustainable Homes). Air leakage rates of
1 m3/(h.m22) at 50 Pa will be necessary
for these homes. While this sounds like
science fiction today, the Canadians do
already achieve this performance from
timber frame and panellised systems.
To book testing from NHBC contact
airleakagetesting@nhbc.co.uk or
telephone 0844 633 1000.
ACTION
Bar chart showing results of sample air leakage tests
The aspirational standards of 3
m3/(h.m2) at 50 Pa will be difficult to
achieve consistently. It is apparent from
our results that these permeability
targets will require changes in materials
and processes. CLG’s ‘Accredited Details’
establishes a quality control blueprint.
Although Accredited Details have been
simplistically viewed as specification
templates, they are very dependent on
quality control processes. The benefit of
adopting Accredited Details is the promise
of a reduced compliance testing regime.
By adopting this approach the emphasis
shifts for compliance testing just prior
to completion to a process encompassing
best practice or prototype designs, the
discipline of quality checks, inspection
and record keeping. These processes
will consistently deliver reduced air
permeability and remove the potential
last minute surprises inherent in
pre-completion testing.
Ensure you have built in
accordance with the design
and have completed the
airtightness test in readiness
for producing the Energy
Performance Certificate prior
to the pre-handover inspection.
Issue 41
May 2008
Sustainability
As part of the response to
climate change, sustainability is
set to continue to be a hot topic.
Amidst a range of legislative
requirements being introduced
for housing, the complexity
affecting developers, builders
and housing associations
alike continues to increase.
Key legislative requirements
Introduced as a voluntary national
standard in 2007, the Code for
Sustainable Homes became mandatory
on all new homes from 1 May 2008.
Prior to that, Energy Performance
Certificates have been required on
all new homes completed from 6 April
2008. That date is also the trigger for
all homes needing a Home Information
Pack when first marketed.
Whilst there are separate regulations for
each, there is also considerable overlap
and a chance to integrate operations
to establish an efficient solution.
The Code for Sustainable Homes
This involves assessment of performance
in 9 key areas at design stage, plus a
post construction stage review before
the full Certificate can be issued.
The latest announcement requires
developers to declare the Code rating
of a new home in the Home Information
Pack, by including either a full formal
Code assessment certificate or a
Nil-rated certificate.
An amendment to the HIP regulations
has been made. This confirms that the
requirement applies to new homes for
which the local authority receives the
building notice, initial notice or full
plans for Building Regulations after 1
May 2008. The enforcement powers
will rest with Trading Standards.
ACTION
In some circumstances, a minimum Code
level must be achieved. Properties on
English Partnerships land or those with
2008-11 Housing Corporation grant
funding need to achieve Code level 3
as a minimum.
Further, the HIP service can combine
smoothly with the Energy Rating
and Code services to minimise the
complexity and save you time.
Energy Performance Certificates
EPCs became mandatory in 2007
as part of the sale of existing homes.
The requirement was extended to
new build in England from April
in accordance with the European
Performance of Buildings Directive.
The Code does not apply in Scotland
As new build often sell off plan,
the Predicted Energy Assessment,
calculated from the SAP at design
stage, should be included in the HIP.
Northern Ireland now requires
Code Level 3 for all public
sector housing.
The National Assembly of Wales
announced in December 2007 that it
will be adopting the Code for all new
social housing. Welsh Ministers are
expected to confirm shortly
the timing and Code level.
Once the property is physically complete,
your accredited new build SAP assessor
will need to be informed of any design
changes and Air Leakage test results in
order to produce the final EPC. That
certificate should be given to the new
homeowner and also Building Control,
who will be obliged to operate a “no
certificate, no completion” policy; though
it will not hold up CML certification.
Home Information Packs
After a phased introduction during 2007,
HIPs are now required on all homes first
marketed from 6 April 2008, when
the exemptions for new homes built to
2006 Building Regulations ended.
A HIP must include the Energy
Assessment, Local and Water Searches,
Sales Statement and Title deeds, plus
Leasehold information where appropriate.
It is possible to provide the HIP
electronically, though consumers are
entitled to ask for additional printed copies.
EPCs become mandatory
Given the multiple documents required
in a HIP and their multiple sources, a
simple and efficient process is needed
to monitor progress and quickly produce
HIPs, which can be over 150 pages long.
The NHBC New Build HIP service is
tailored to developers needs. This fully
managed web based solution minimises
the administrative burden and costs
associated with compiling HIPs and
includes the mandatory searches in
a very cost effective manner.
For more details see our website which will be updated as further
clarification becomes available from the Government.
www.NHBCbuilder.co.uk/consultancyservices
HIPs required on all new homes
5
Standards
Extra
Fire safety survey – lessons to be learnt
In autumn last year, as part
of our ongoing programme
of surveys into construction
practice, the fire safety
features of the common parts
of flat blocks were examined.
Overall, the results indicate that fire
safety is given the consideration it
requires, with critical areas of buildings
being well designed and constructed.
But we cannot afford to be complacent
about fire safety, and all areas need a
consistently high standard of build quality.
Fire cladding
Plasterboard is widely used as a fire
protecting material for both structural
elements and partitions. It is important
that the correct type and thickness of
board is used for the fire resistance
required. Generally where thinner boards
are specified they need to be the fire
resistant type, and more than one
layer may be needed to provide the
appropriate fire resistance.
Fixings
Fixings are of great importance and
most boards will require nailed or
screwed fixings into the timber or
lightweight steel structure. Cladding
structural elements such as steel beams
and columns may need specific fixings
or even a sub-frame around the element
for fixing the board and it is vital that
the manufacturers’ details are followed.
This applies to proprietary systems as
well, because both have been tested and
rated using specific fixing specifications.
Fire stopping
Due to the natural movement of buildings
it is not always possible to butt
fire-resisting boards to elements of the
structure. In these cases the expansion
gaps need to be filled with a suitable
fire resisting flexible material such as
intumescent mastic.
evidence they have been successfully
commissioned. Close co-operation is
vital to ensure tests and certificates
are completed and witnessed before
occupation of the building.
Where services penetrate fire resisting
enclosures such as walls from service
shafts and common corridors into flats
the gaps around the pipes and cables
are often filled with foam. Ensure the
foam is certified as fire resisting and
installed in accordance with the
manufacturers’ specification. Some fire
resisting foams require over spraying
with another coating (sometimes
intumescent) in order to provide the
minimum fire resistance.
Fire doors
Whilst the fire rating and ironmongery
of the vast majority of riser/service
cupboard doors were found to be adequate,
it is of concern that in over a half of the
cases surveyed the signage to these
doors had been omitted. Signs that read
“Fire Door Keep Shut” or “Fire Door
Keep Locked Shut” should be fitted to
all such doors. Please remember that
corridor doors also need to have
“Fire Door Keep Shut” signs fitted.
It may be more appropriate to use a
mineral fibre quilt to seal openings, and
in these cases the fibre will need to be
tightly packed to achieve a suitable fire
seal. For larger penetrations such as
ductwork and other service pipes
penetrating an enclosure (walls and
floors) intumescent collars may be
required. These collars need to be
correctly located, adequately fixed to
the supporting structure (the pipe must
not support the collar), tightly sealed
and of a suitable type for the application.
Collars that are not mechanically fixed
around a pipe/duct will need to be built
into the wall or floor that they penetrate
by solid construction such as concrete.
Without a solid surrounding structure
the intumescent material may expand
outwards (instead of inwards) and fail to
seal the void within the pipe/duct.
Whilst the provision of a communal
area for post boxes is popular, there
are still a number of flat entrance doors
that have individual letter plates fitted.
Where this is the case it is important
to fit a suitably fire resistant letter
plate to maintain the fire resisting
integrity of the door.
Venting and lighting
Where NHBC are providing Building
Control, our Inspectors are not only
witnessing a large number of
emergency lighting and automatic
venting system tests but are seeking
Ceilings
A growing practice is to fit a false
ceiling (usually plasterboard on metal
supports) throughout a flat prior to the
internal stud partitions being installed.
These ceilings are often unlikely to
achieve 30 minutes fire resistance and
where “protected entrance halls” within
the flats are required for means of
escape, the fire line needs to extend into
the space within the false ceiling void.
The fire resistance of this line is normally
a minimum of 30 minutes and can be
achieved by extending the partition
construction or by other proprietary
methods such as a reinforced mineral
fibre cavity barrier. Any services/ducts
passing through this area will need to
be of rigid metal or suitably fire-stopped.
Attention to detail is key to providing a building that will resist
the spread of fire.
Ensure that:
the manufacturers’ specification for claddings are followed
the correct fire stopping product is used for the specific circumstances
An example of a good fire seal
6
ACTION
the completeness of walls and ducts is checked before handover
life safety systems are commissioned with evidence provided to
Building Control.
Remember one mistake can cost lives.
Issue 41
May 2008
New guidance on radon
Radon is a naturally occurring radioactive gas
that can only be detected by suitable equipment.
It has no long-term harmful effects on people in
the open air. However, building homes in an area
at risk from higher concentrations of radon means
that the gas can become a risk to the occupants.
The guidance document on radon protection was last revised in 1999 and
incorporated maps of areas at a higher risk and details of suitable protection.
The Building Research Establishment (BRE) have now released the latest version
of the document that provides the most up to date information and guidance.
In brief, the main changes are:
one set of improved and simplified maps (1km grids)
inclusion of non-residential buildings
inclusion of extensions, converted and refurbished properties
protection of buildings with timber floors.
The basic and full protection options remain. Basic protection includes the
installation of a suitable barrier over the whole of the footprint (e.g. minimum
1200 gauge membrane), and full protection includes the provision of ventilation
under the floor (e.g. ventilation of a void or provision of a sump). The guidance
gives details to assist the designer.
So, no matter what type of building is being constructed, check to see if it will
be in an area at risk from radon and incorporate suitable protection measures.
Indeed, even if replacing the ground floor construction of an existing building,
installation of a barrier should be considered.
Current information from BRE
The new maps give an assessment of the most onerous radon protection
requirement based on the highest radon potential within the 1km map grid,
though it may be possible to adopt a lower level of protection if a site specific
radon report is commissioned which considers the specific site geology.
Ensure you are prepared
The new guidance applies to all extensions, including conservatories, covered by
the Building Regulations.
follow it immediately.
to meet the revised radon
guidance from 1 September
2008 and if practicable
The revised guidance is
For conversions and refurbishments of non-domestic properties to residential
use, the new guidance advises that radon protection should be considered and
installed as far as reasonably practical. Our surveyors and inspectors will work
closely with you to achieve the best outcome.
Press (01344 328038 or
brepress@his.com. However
should you have any queries
regarding residential sites
please don’t hesitate to
ACTION
When will you need to design and build to the latest guidance?
Although no date has been given about implementation of the new version of
BR 211, NHBC considers that from 1 September 2008 any dwelling, where building
work has not commenced, should follow the guidance in the 2007 version of
BR 211. This coincides with the effective date for NHBC Standards. Between
now and 1 September you are free to choose which guidance to follow but of
course you are strongly encouraged to follow the latest version.
available from the IHS BRE
contact your NHBC surveyor
or NHBC Engineering on
0844 633 1000.
7
Q
STOP PRESS
External steps
– mobility access
Are there circumstances where
external steps with a total rise
of less than 600 mm should be
provided with a hand rail?
A
Yes, Approved Documents M
(England and Wales) requires a
handrail on one side of a flight of
steps to the principal entrance of a
dwelling where the flight comprises
three or more risers. The rise of
each step should be uniform and
between 75mm and 150mm.
Access to gas flues revisited
Since this issue was raised in Standards Extra’s 38 (April 2007) and 39
(August 2007), some confusion has arisen regarding the provision of
access to room-sealed fanned draught flue systems, particularly where
the flue pipes are concealed in voids. The previous advice still stands.
However, CORGI Technical Bulletin 200, dated June 2007, clarifies what is needed
to meet the requirements of the Gas Safety (Installation & Use) Regulations to allow
the installer and servicing operatives to be able to check that:
The handrail should be 850mm to
1000mm above the pitch line of the
flight, and extend 300 mm beyond
the top and bottom nosings.
the flue is continuous throughout its length
Q
To achieve this, as a minimum, it is necessary to be able to visually inspect the flue
system throughout its route, both prior to initial commissioning of the appliance
and subsequently during routine servicing or maintenance of the appliance, in
order to verify the correct installation and completeness of the flue system.
Practically this means that any flue ducting, covering or false ceiling needs to be
provided with access points at changes of direction and at strategic positions to
allow all joints to be inspected. If these are not provided the engineer cannot confirm
that the installation is correct and safe to use, and will be unable to complete
the commissioning of the appliance and issue the required documentation.
Dry linings to walls
Can dry lining be fixed using
adhesive dabs to walls that
have received a chemical
injected damp proof course?
A
Plasterboard manufacturers
recommend that adhesive
dabs should not be used if the
background may be damp.
Walls that have received a chemical
injected damp proof course may
take a considerable time to dry to
an acceptable moisture content.
Contamination on the surface of the
wall, such as salts may affect the
bond of the adhesive to the wall.
all joints are correctly assembled and are appropriately sealed
the flue is adequately supported throughout its length.
It is also important to note that CORGI Technical Bulletin 200 has now been
incorporated into the new version of BS 5440-1: 2008 Flueing and ventilation for gas
appliances of rated input not exceeding 70 kW net (1st, 2nd and 3rd family gases)
— Part 1: Specification for installation of gas appliances to chimneys and for
maintenance of chimneys.
At the time of pre-handover inspection, appropriate certificates provided by
a competent person must be shown to the Building Inspector in order for
the property to be finalled for warranty and building control purposes.
Hydroscopic salts in the wall may
attract moisture that can break
down the adhesive.
No, dry lining should not be fixed
using adhesive where the walls have
previously suffered dampness.
It should instead, be fixed to treated
timber or metal firrings. These
should be mechanically fixed to
the wall over strips of vertical dpc.
If you are contemplating the installation of
room-sealed fanned draught flue systems within a concealed void, take
advice from your CORGI registered installer or talk to CORGI Technical
Services on 0800 915 0499.
ACTION
QUESTIONS
Standards
Extra
Make sure that the flue pipe ducting and coverings have access panels
provided at the appropriate points, and that a commissioning
certificate for the boiler and flue system is completed and available for
checking by the Building Inspector at pre-handover stage.
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: technical@nhbc.co.uk
8
HB2421 03/08
1
Sustainability
Extra
May 2008
Welcome to:
‘Sustainability
Extra’, a regular
update from NHBC
on issues related
to the environment,
energy and all
things sustainable.
In this issue there is a brief
summary of a seven-year
research project led by experts
from Leeds Metropolitan
University which has been
looking at the issues associated
with designing and building
masonry homes to high energy
efficiency standards.
It is becoming increasingly
clear that microgeneration has
a significant part to play in
delivering future low and
zero-carbon homes. There is an
article signposting two reports
recently published by the NHBC
Foundation, that will be of
interest to designers and builders
looking at microgeneration.
There is also a ‘news’ section
that highlights some recent
developments in sustainability
that will be of interest to the
house-building industry.
Neil Smith,
Group Research and Innovation Manager
Stamford Brook
Evaluating the impact of an enhanced
energy performance standard on loadbearing masonry domestic construction
Images © Leeds Metropolitan University – A general view of Stamford Brook
NHBC has supported and provided
funding for this important research
project since its inception in 2001.
The project was government
sponsored and included participation
from several public and private sector
organisations, including a major
contribution by two house builders.
The project has recently concluded
and reports detailing the findings
have now been posted on the
internet. They will be of particular
value to house builders designing and
building homes to comply with the
Code for Sustainable Homes and will
inform deliberations about future
changes to building regulations.
Background
Stamford Brook is a development of
around 700 cavity masonry dwellings
being constructed on a 25-hectare parcel
of the National Trust’s Dunham Massey
Estate near Altrincham in Cheshire.
Construction on the site commenced
in 2004 and is expected to continue
until around 2009/2010. The development
is being carried out under a partnership
agreement between the landowner,
the National Trust, and the two
house builders – Redrow and Bryant
Homes (now part of Taylor Wimpey).
The house builders have been
working closely with the Centre
for the Built Environment at Leeds
Metropolitan University, which has
been investigating various aspects
of the design and construction
processes. The research project
team has followed the progress of the
development from initial discussions
on standards for energy efficiency
and environment, through the
detailed design process, observation
of construction of the dwellings,
performance testing of completed
buildings and monitoring of
occupied houses.
>>>
Sustainability
Extra
The overall objective was to
support future reviews of Approved
Document L (England and Wales)
by evaluating the various impacts
on a large scale masonry housing
development on a range of
improvement measures that could
be used to meet the requirements
of an advanced energy performance
standard. The project considered
the following issues:
technical impact
economic impact
regulatory issues
design process issues
site project management and
construction process issues
performance in-use.
The study demonstrated that,
provided sufficient care is taken
with both the design and the
construction processes, cavity
masonry construction is perfectly
capable of delivering the
specified target air permeability
of 5 m3/(h.m2) @ 50 Pa. Indeed,
parged masonry walls linked to
airtight top floor ceilings and
ground floors and well designed
construction details, could deliver
airtightness that is consistently
below 2 m3/(h.m2) @ 50 Pa.
‘Party wall thermal bypass’
Experiments undertaken showed
that the cavity of a separating
wall between homes can provide
the route for significant heat loss.
Analysis of the experimental data
Energy performance standards
The energy performance standards set were intended to ensure that
homes built would be around 10% to 15% better than that required
under Part L1a 2006, depending upon dwelling form and size.
Standards adopted were as follows:
Element/Parameter
Requirement
Exposed walls
U-value: 0.25 W/m2K
Roof
U-value: 0.16 W/m2K
Floor
U-value: 0.22 W/m2K
Windows, doors
and rooflights
U-value: 1.3 W/m2K;
max area 25% of gross floor area
Air permeability
5m3/(h.m2) at 50 Pa
Carbon intensity of
70 Kg CO2/GJ useful heat – heating system this equates
to a minimum gas condensing boiler efficiency of 85%
Window reveal
Cavity width 140mm
for blown fibre insulation
2
Thermal imaging – note the heat loss
(red area) around the balcony threshold.
showed that the mechanism
for heat loss via the separating
wall is driven by air movement
in the cavity. This air movement
is generated by thermal stack
effects and by pressure differences
caused by the action of wind
moving across the dwelling.
Measurements have shown that
the separating walls at Stamford
Brook have an effective U-value
of around 0.5 W/m2K to 0.7
W/m2K. Clearly this finding has
implications for both new
homes and the existing stock.
The gap between
designed performance
and as-built performance
Testing showed that there was
a significant gap between the
expected energy performance of
the dwellings as designed and the
reality of the energy performance
as they were constructed. A large
proportion of the difference was due
to the party wall thermal bypass
but some was due to deficiencies
in the construction, which were
highlighted through close
examination during construction
and testing after construction.
Testing showed that the as-built
U-values of the floors, walls and
roofs were higher than calculated.
Infra-red thermal imaging of the
completed houses was particularly
useful and demonstrated the
importance of good design
and careful construction in
minimising thermal bridging.
In addition to the technical
findings the research highlighted
the need to look very carefully
not only at the technology but
also the design and construction
processes through which the
technology is applied. It is argued
that as we move towards low and
zero carbon housing standards,
improving the whole production
process will be as important as
the development of improved
technological solutions.
ACTION
Airtightness issues
>>> Project objectives
Detailed information on the
Stamford Brook research
project is available at:
http://www.leedsmet.ac.uk
/as/cebe/projects/stamford
/index.htm
Issue 1
May 2008
NHBC Foundation
The Foundation has recently
launched three new reports ‘Zero
carbon: what does it mean to
homeowners and housebuilders?’,
‘Ground source heat pump systems’
and ‘A review of microgeneration
and renewable energy technologies’.
These reports complement the
‘NHBC guide to renewable energy’
published in May 2007, which can be
downloaded at www.nhbcbuilder.co.uk
(see ‘publication download’).
Zero carbon: what does it mean to
homeowners and housebuilders?
This is a market research survey of
consumer and builder attitudes to
and understanding of zero carbon.
The consumer research focussed
on ascertaining attitudes towards
zero carbon and identifying levels
Some NHBC Foundation publications
of understanding along with
thoughts and feelings on the
potential impact that zero carbon
homes may have on lifestyles.
Ground source heat pump systems
Ground source heat pump systems
take low level heat energy created by
solar gain in the near surface layers
of the earth, to extract energy that
can be used for space and water
heating. This guide explains how heat
pump systems work and considers
issues of specification and design.
It also looks at the benefits of
installing these systems and barriers
to their widespread adoption.
A review of microgeneration and
renewable energy technologies
This report was commissioned
to help builders, developers and
local councils meet the 2016 zero
carbon homes target. It compares
and contrasts the various
technologies currently available,
including biomass, photovoltics,
solar hot water, wind power, heat
pumps and combined heat and
power. Each technology is briefly
described and key design and
installation considerations outlined.
Data tables are included which
estimate potential costs and
benefits of each.
ACTION
The NHBC Foundation
was established
in January 2006.
Focusing on the new
homes industry, it
facilitates research and
development, technology
and knowledge sharing,
and the capture of
industry best practice.
These and the other reports
from the NHBC Foundation
can be downloaded at
www.NHBCFoundation.org
(see ‘Projects’)
The Energy Saving Trust (EST) has recently published the first in a suite of guides that provides
technical guidance on designing and building new homes that meet the energy requirements of
the Code for Sustainable Homes. This guide addresses energy efficiency measures to meet, and in
some instances, exceed minimum measures set down in Code level 3. Further guides to address
energy efficiency measures under Code levels 4, 5 and 6 are in the process of being developed
and will be available within the next few months.
NEWS
Energy Saving Trust publishes
‘Energy efficiency and the Code for Sustainable Homes’
The guide is available from the ‘housing and buildings’ section of the EST website at www.est.org.uk
3
Sustainability
Extra
Code for Sustainable Homes
NEWS
The Technical Guide to the Code for Sustainable Homes
has been revised and republished. The April 2007
version is available from the Planning Portal website at
www.planningportal.gov.uk (see Building Regulations section).
In July 2007 the Government consulted on proposals for making
it mandatory for new homes in England to be rated against the
Code for Sustainable Homes. This would mean that, once introduced,
all homes would either have to be assessed against the Code and
given a certificate indicating the rating they had achieved or would
not be assessed and would be deemed to have achieved a zero rating
against the Code. The intention of the proposal was to provide
information that would inform purchasers’ decisions to buy.
Following the outcome of the consultation the Government
announced that it will implement mandatory rating against the
Code for all new homes from 1 May 2008. Futher information is
available from the Communities and Local Government website at
www.communities.gov.uk/planningandbuilding/theenvironment/
Microgeneration
Certification Scheme (MCS)
In Standards Extra 40 (December 2007)
we reported on this scheme which has now
been renamed from ‘UK Microgeneration
Certification Scheme’. The name change is
intended to clarify that the scheme is not
limited to UK industry. The certification mark
is being amended to reflect this change and to
incorporate the new BERR (Department for
Business, Enterprise and Regulatory Reform) logo.
NHBC supports this scheme, which
demonstrates that microgeneration systems
and their installers have been satisfactorily
assessed by an independent authority.
We believe it is the best way of ensuring
that installations will meet homeowners’
reasonable expectations and deliver their
expected environmental benefits without
any unintended consequences.
Full information on the scheme is available
at www.ukmicrogeneration.org.uk
4
Code for Sustainable Homes
‘Merton rule’ Bill
A private member’s bill has been put
forward proposing a right for councils
to set policies, which insist on a minimum
level of power for a development to be
generated by on-site renewable technology.
The policies, which have now been
proposed by about 100 councils,
are based on an approach piloted
by Merton council in London.
The private member’s bill follows strong
lobbying by the house building and
construction industry (including NHBC),
which has argued that a variety of different
local regulations will make it harder to
achieve the industry’s overall zero-carbon
target by 2016. We also consider that it is
appropriate for carbon emissions to be
regulated through Building Regulations
as opposed to planning legislation.
HB2427 03/08