Standards Extra - NHBC Home

NHBC’s technical newsletter
Standards
Extra 43
December 2008
This edition includes:
Guidance on insured
guarantees for remedial works
Making sure gable walls
are properly tied
Sustainability Extra - Issue 03
Choosing the right
grade of slate

Standards
Extra
CONTENTS
2/3
NHBC Standards
for Conversions
and Renovations -
Insured Guarantees
3
Showerheads
over baths
4
Closed or
mothballed sites
5
Gable walls -
the importance
of restraint
6
Slates -
no more grey areas
7
Secure escape
8
Cast stone to
be recognised in
NHBC Standards
8
Questions
and answers
NHBC Standards
for Conversions
and Renovations –
Insured Guarantees
In Standards Extra issue 32
(April 2005) we took a look
at the updated Standards for
Conversions and Renovations
that became effective in
September 2005.
Since that time the Standards have
provided an integral part of NHBC’s risk
management of such projects. However,
we continue to receive a number of
enquiries about the part of the Standard
that deals with insured guarantees/
warranties for specialist remedial works.
Those who regularly use the Standards for
Conversions and Renovations will know
that Clause C5 sets out our requirements
for insured guarantees/warranties.
The following text is extracted
from that Clause:
“Proprietary remedial treatment relating
to wood rot, beetle infestation, dampproofing,
structural waterproofing
(tanking), wall tie replacement and other
specialist work shall be the subject of a
suitable insured guarantee/warranty”.
The clause goes on to require that
the guarantee/warranty should:
■ be provided by the
specialist contractor
■ cover any failure of the work
■ cover any consequent opening
up and making good
■ remain valid for a minimum
period of 20 years
■ be in favour of the home owner
(provided it is automatically
transferred at no cost to
subsequent owners) and NHBC.
Finally Clause C5 requires that:
■ ”the specialist contractor’s obligations
should be covered by an insurance
policy issued by a UK regulated and
authorised insurer, which includes
cover against the specialist contractors
insolvency and that the insurance policy
should specify the property covered”.
A typical conversion project
2

Issue 42
September 2008
Problems
Remedial works in progress
Clauses C6, C9 and C13 of the
Standards go on to confirm that:
“Members of The Property Care
Association (PCA), a division of the British
Wood Preserving and Damp-proofing
Association (BWPDA) backed by the
Guarantee Protection Insurance Ltd (GPI)
meet the requirements of Clause C6”
During the last 3 years we have
received contact from a number of
other contractors and some insurers
asking if NHBC would consider
alternatives. But, disappointingly on
reviewing their schemes we found
that none fully met the level of cover
required in the Standards or that
provided by the PCA/GPI scheme.
Claims spend on converted or
renovated homes continues to be
disproportionately high when compared
with new build. The above images show
just what can go wrong with specialist
works! So making sure that insured
guarantees/warranties are set up
correctly to provide adequate cover for
homebuyers, builders and NHBC when
things do go wrong is imperative.
In April this year we carried out an
exercise to review the various alternative
insured guarantee/warranty schemes
known to us, by inviting some 30 or so
specialist contractors and insurers to
complete a detailed questionnaire. We
askedthemtoconfirmthelevelofcover
their scheme provided and importantly
whether, in their view, this complied
in full with the NHBC Standards for
Conversions and Renovations. Following
a thorough review of the 20 or so
contractors and 3 insurers who
responded, we were not able to identify
any companies who matched (or bettered)
the cover needed to meet our current
requirements, other than PCA/GPI.
However, a recent submission from
Construction Guarantee Services
Ltd (CGS) was found to also meet our
requirements. CGS require their
contractors/members to meet with
the Accredited Wykamol User Scheme
requirements as a benchmark for technical
competence, and also that CGS perform
an ongoing vetting process broadly
in line with our requirements.
We have also established that the CGS
guarantee/warranty is backed by Milburn
Insurance Company Ltd and this meets
our requirements for insurance. We have
therefore agreed that a CGS contractor/
member backed by Milburn Insurance
canbeconsideredasanacceptable
alternative to the PCA/GPI cover.
Naturally, we feel that competition in
this area is extremely important and
therefore should any other insurers or
contractors come forward with schemes
that comply in full with our Standards
for Conversions and Renovations we
would be pleased to include them as
an acceptable alternative.
ACTION
If you intend to engage
specialist contractors
to carry out any of the
remedial work detailed on
page 2, make sure they can
provide a suitable insured
guarantee/warranty that
is acceptable to NHBC.
Showerheads over baths
Where builders provide a showerhead over a bath
dotheyneedtoprovideascreenandtilethewalls?
This long running issue has now been resolved by NHBC’s
Standards Committee who consider it reasonable that water should
be contained (and not go over the bathroom floor) and the walls
around the bath should be tiled where water will fall on them.
Where builders provide a showerhead over a bath, or the
fixing for a showerhead such that people can stand under it,
then builders will be required to provide a screen or other
suitable means to contain the water.
Additionally the surfaces that may be wetted by persons
using the shower facility will need to be tiled or have an
equally water resistant finish.
This is nothing more than most builders already provide but it
will be incorporated into NHBC Standards at the next reprint.
ACTION
Builders are asked to note that this will be
incorporated into the Standards in due course.
Where BI’s come across this scenario in the interim
the builder will be advised of the forthcoming change
and asked to comply with the new requirements. This
will be noted as an observation in the Site Record Book.
3

Standards
Extra
Closed or mothballed sites
The current downturn in construction activity is resulting
in a number of sites and plots being closed or mothballed.
Past experience shows that where this
has not been done correctly, it has resulted
in substantial future claims costs for
both builders/developers and NHBC.
At any stage of construction it is
vitally important that appropriate
precautions are taken to ensure
the durability and likely in-service
performance of materials, products and
systems is not impaired by the process
of being closed or mothballed. To ensure
potential issues are fully considered
builders/developers should produce a
practical site closure plan. The plan
should consider the following aspects:
Foundations and substructure
Where plots are closed just after the
foundations have been installed action
should be taken to provide protection
to ensure that rain, ground water,
drying weather and frost cannot
adversely affect the foundations.
Where specialist foundations and
ground treatment have been employed
and left exposed the designer should
be consulted for advice.
Weatherproofing
Where possible, dwellings should be
made fully weathertight. Where this is
not achievable cavities should be closed
to avoid water and debris accumulating
andtoprotectanycavityfillalreadyin
place. The protection of exposed
timbers including all types of sheathing,
plywood, flooring elements, joists, and
roof members is also very important.
Particular attention should be given
to timber frame construction and the
possible problems associated with
increased moisture content of the
4
A mothballed site
timber over long periods. Temporary
sealing of openings in the envelope will
be required for both weatherproofing
and security. Additional items to be
considered include the provision
of temporary sealing to prevent
infestation by insects and rodents.
Ventilation
Where plots are closed it is very
important to ensure adequate
ventilation is provided to prevent
possible fungal attack and mould
growth to floors, walls, roofs, ceilings,
fixtures and fitments.
UV degradation
Materials that may be adversely
affected by the effects of solar UV
should be protected to avoid premature
degradation. Materials could include
dpm’s, dpc’s and roofing felts (including
vapour permeable underlays) which
would normally be covered.
Drainage
Plots that have completed roof
coverings in place should also have
all rainwater guttering and downpipes
completed and connected to a suitable
outfall to prevent the possibility of
damage caused by excess water
running over external walls etc.
Site security
You must be mindful of any health
and safety risks presented by the
vacant site. The Principal Contractor
maintains a liability for the safety of
anyone on the site regardless of
whether or not they are lawfully there.
Because of this, it is important to leave
thesiteinassafeastateaspossible
as well as taking measures to prevent
access to the site.
Fencing should be continuous around
the site and panels should be of the
anti-climb type and double clipped to
make access difficult. Where the risk of
intruders is high a solid hoarding with
furthersecuritymeasuresmaybe
appropriate. On site you should make
sure any structures are safe and if
possible remove all scaffolding from the
site. If scaffolding remains make sure all
ladders are removed, or locked out of
sight. No excavations and manholes
should be left open. Securely covering
manholes and filling excavations is ideal,
but if this is not possible, openings
should be adequately fenced off.
Ensure any plant is removed from site
or locked securely in the compound if
removal isn’t practical. Ideally materials
left on site should be kept to a minimum,
whatever is left on site should be stacked
safely within a storage compound or
locked in storage containers.
Even when the site has been
mothballed it is still the Principal
Contractors responsibility and regular
checksmustbemadetoensurethe
perimeter is secure and to check for
any signs of trespass or damage.
Storage
It is important that materials and
products are correctly stored in an
appropriate manner to ensure their
durability and design life is not
compromised and to ensure Health
and Safety and security issues
mentioned above are addressed.
Inspection
NHBC staff (normally Building Inspectors)
will advise builders/developers of the
precautions to be taken when sites
and plots are closed or mothballed as
detailed above. These are practical
measures to mitigate damage to plots
at all stages of construction ensuring
that when work restarts damage is
avoided or at the very least kept to
a minimum.
ACTION
Where sites and plots
are closed or mothballed
an appropriate closure
plan, taking account of the
above, should be developed
and implemented by
builders/developers to
reduce the risk of
additional cost when
work re-commences.

Issue 43
December 2008
Gable walls - the importance of restraint
When the wind blows parallel to gable walls
it generates negative pressures on them.
If the gables are not adequately built and
connected to the roof structure these
negative pressures can ‘suck-out’ the gable
walls resulting in catastrophic failure.
This has occurred on a number of sites recently during
high winds and has highlighted the importance for
gables to be correctly constructed and restrained.
The common practice of using trussed rafters leads to a
situation where none of the roof self-weight (traditionally
from purlins and binders) passes into the gable wall.
With this form of construction the lateral restraint to the
gable has to be provided by adequate strapping at the
verge (or by a gable ladder) and at ceiling level if
required (see strap location diagram). The restraint
must be correctly detailed and installed.
As well as providing lateral restraint to gable walls,
strapping also contributes to the robustness of the
building and reduces the sensitivity of the building to
disproportionate collapse in the event of an accident.
Restraint straps therefore provide a critical function.
The following diagrams show an acceptable method
of satisfying building regulations for residential dwellings
not exceeding 3 storeys.
Where these dwellings exceed 3 storeys and have
been designed in accordance with BS5628-1:2005
(Code of practice for the use of masonry) the connections
to gable walls should be provided at intervals of not more
that 1.25m centres for all storeys or as specifically
required by the design engineer.
Effective strapping at ceiling level
Effective strapping at verge
Strap location
Ensure that:
Collapsed gable wall
ACTION
The straps are installed and fixed fully in accordance with
the building regulations guidance and in accordance
with manufacturer’s and designer’s requirements.
Rafters are not notched to make the straps flush with the rafter.
The strap goes under the rafter and over ceiling joists.
At the verge the strap turndown should be on a substantial
piece of blockwork, preferably the centre of an uncut block.
The strap should turn down vertically a minimum of 100mm
and be tight against the face of the inner leaf wall.
Packing should be provided, at the strap position,
between the inner leaf and the first truss.
Noggings (dwangs) are provided and set horizontal unless the
strap has pre-formed twist to line it up with the roof slope.
A high level of workmanship is maintained throughout the construction.
5

Standards
Extra
Slates – no more grey areas
For many years slate roofs have been
acknowledged as the premier roof
covering for pitched roofs but in recent
times there have been concerns about the
durability and appearance of certain slates.
The change from the British Standard,
BS 680 to European Standard BS EN
12326-1 and -2 has resulted in a need
for the user or specifier to specify what
level of performance and durability they
want. Whereas BS 680 gave a simple
pass or fail for several tests and two
quality ‘grades’ BS EN 12326 does not.
Because of the wide range of qualities
of slate which are acceptable throughout
Europe, each with different durability, it
provides a set of levels of performance
against a series of tests. The user
can and should choose what level of
performance they want for each test.
To address this issue NHBC has been
working with the industry to establish what
should be the minimum specification to
meet with NHBC Standards to ensure
the product has acceptable durability.
Under BS EN 12326 consignments of slates
should now have an “accompanying
commercial document (ACD)” from the
producer/supplier indicating the slate’s
performance. An example of the full ACD,
containing an explanation on the
information it should provide, can be view
at www.stoneroof.org.uk/tests2.html
Below is an example of the first page of
the ACD together with the level of test
results that NHBC now looks for to
meet our Standards.
Accomanying commercial document -
Information requirements
Producer – Sufficient details are required
to identify the producer/supplier.
Number of this commercial document
– This can be a number issued by the
test house or the producer/supplier.
Date of issue – The ACD should be
relevant for the batch of slates being
supplied. Retesting and updating of ACD’s
should be carried out at least once a year
and more frequently where large volumes
of slates are being extracted and for every
new source or vein of rock extracted.
Commercial document issued by –
this can be the test house or the
producer/supplier.
Location of mine or quarry –
required for traceability of slate.
Date of sampling & date of testing –
If more than one date is applicable to
sampling and testing they should be
indicated against the individual test results.
The sampling and testing dates should
be as close as possible to the ‘Date of
issue’ of the ACD. The ‘Date of issue’
should be used to establish when further
sampling and retesting is required at the
frequencies set out in NHBC Standards.
Product description & commercial name
– Name or description given to slate
by the producer/supplier.
Dimensional tolerances – These are
to be within those set down by the
Standard. Note: Slates, which fall within
the tolerances, still require proper
selection and fixing on site to achieve
an acceptable finished roof covering.
Nominal thickness – Thickness of
the roofing slates, as declared by
manufacturer and the amount
by which individual thickness varies as
a percentage of the nominal thickness.
Characteristic modulus of rupture (MoR)
– a measure of the slate’s mechanical
strength both along and across the slate.
Slates from weaker rocks may need
to be supplied thicker than those
from stronger rocks to
achieve a satisfactory
performance in use.
The Standard provides
equations, which are
used to establish the
minimum slate thickness.
The minimum thickness
is calculated using the
CMoR and a National
(i.e. UK) factor, which
takes into account the
weather conditions of
the country of use.
It is the producer’s/
supplier’s responsibility
to ensure all the slates
in a consignment are
at least as thick as the
minimum value obtained
using the UK factor.
Water absorption
– For compliance with
NHBC Standards the
water absorption should
be no greater than
0.6% i.e. A1 code.
Freeze thaw – This test is
not required when slates
have a ‘Water absorption’ no greater
than 0.6%
Thermal cycle – This is a test for
reactive metallic minerals within the
slate, which may cause staining, pitting
and/or delamination and potential failure
of the slate. For compliance with NHBC
Standards a slate should achieve a T1 code.
Carbonate content – High carbonate
content can cause colour changes in
the slate and potential for accelerated
erosion and break down. For compliance
with NHBC Standards a slate should
achieve a S1 code.
Note: It is acknowledged that some slates,
that do not achieve a S1 code, have a history
of satisfactory performance for at least
60 years in the UK. If such a slate is being
considered please discuss its acceptance
with NHBC Technical in the first instance.
Non-carbonate carbon content – to meet
the standard this should be less than 2%.
Exposure to fire, reaction to fire
& release of dangerous substances –
Roofing slates meet these requirements.
An abbreviated version of the ACD,
as shown in BS EN 12326 should also
be attached to each crate of slates.
Accompanying commercial document
ACTION
Ensure that your slate supplier provides an
accompanying commercial document with each
consignment of slates, and check the slates
have properties at least as good as those
listed under information requirements above.
6

Issue 43
December 2008
Secure escape
In Standards Extra Issue 31 December 2004 we published
an article about locks to individual flat entrance doors.
The article explained the need to provide good security whilst
still providing escape in the event of a fire without the need
for a key i.e. keyless egress. Since that time NHBC has been
working with representatives of the lock industry, police,
insurers and the fire service in developing a suite of British
Standards that cover security and means of escape for all
types of dwellings.
The first British Standard for locks, which addressed enhanced
security for dwellings, was BS 3621 ‘Thief resistant lock assembly
- Key egress’. The Standard covers single point locking
operated by a key from both sides of a door. For locks which
operate without the use of a key on the inside either via a
thumb turn or handle, BS 8621 ‘Thief resistant lock assembly
- Keyless egress’ was developed and published in 2004.
BS 8621 locks provide keyless egress at all times but there
may be times when it would be desirable to lock the internal
thumb turn or handle when leaving a dwelling unoccupied.
This feature is useful in preventing someone breaking in
through a window and removing large items via the entrance
door. To address this a further British Standard, BS 10621 ‘
Thief resistant dual-mode lock assembly’ was developed and
published in 2007. This lock has the facility to lock the
internal thumb turn or handle by an extra operation of the
key from the outside when leaving the property unoccupied.
The latest editions of these three British Standards cover
single point locks for all types of dwelling. In some cases it
may be desirable to fit two locks to achieve sufficient
resistance to forced entry and the recommended lock
functions. An alternative would be to fit a multi-point lock,
which has the same recommended lock functions.
With different dwelling types it is important that the
right lock(s) is fitted to ensure no one can accidentally
become locked in or out of their own property. Below is
a description of the lock functions that should be
used in each dwelling type.
Main entrance door
Dwellings – All
All entrance doors of individual dwellings should be
fitted with one (or more) securely fixed lock and keep
or multi-point locking system, which has:
■ at least 1000 differs
■ a fixing which, if burst open, would not pull
out without breaking the door or its frame
■ a hardened steel bolt or inserts to prevent sawing
■ latch and deadlocking facility.
Locking devices fitted to entrance doors should permit
emergency egress without the use of a key when the
dwelling is occupied.
Any glazing which, if open or broken, would permit release
of the thumb turn by hand or arm entry should be laminated.
Dwellings - With an alternative means of escape.
(These are typically houses with a front and rear door)
Lock(s) should provide initial security by use of a latch
operable with a key externally and a handle/thumb turn
release internally. The full deadlocking facility should be
engaged and be operable with a key externally and a
handle/thumb turn release internally. Locks, which comply
with BS 8621, meet these requirements. External handles
on multi-point locking systems should be split spindle
to avoid operating the latch.
Enhanced security can also be achieved by providing the
facility to deadlock the internal handle/thumb turn when
leaving the dwelling un-occupied. Locks, which comply
with BS 10621, meet these requirements.
Dwellings - Without an alternative means of escape
opening direct to outside. (These are typically ground
floor flats or maisonettes)
The door should be held close by use of a latch operable with
a key externally and a handle/thumb turn release internally.
The full deadlocking facility should be engaged and be
operable with a key externally and a handle/thumb turn
release internally. Locks, which comply with BS 8621, meet
these requirements. External handles on multi-point locking
systems should be split spindle to avoid operating the latch.
Dwellings - Without an alternative means of escape
opening onto a communal access. (These are typically
flats accessed off a communal stairs)
The door should be held close either on a latch operable
with a handle both internally and externally or a roller bolt,
so that the door cannot slam shut locking the homeowner out
without a key. The full deadlocking facility should be engaged
and be operable with a key externally and a handle/thumb
turn release internally. Locks, which comply with BS 8621,
meet these requirements.
Secondary external access doors
The door should be held closed on a latch and operable by
use of a handle both internally and externally. A deadlocking
facility should be operable by use of a key both internally
and externally. Locks complying with BS 3621 meet these
requirements. Alternatively a thumb turn may be used
internally in place of a key operation. Locks complying with
BS 8621 meet these re quirements. In addition bolts should
be fixed securely at both top and bottom of the door on the
internal opening edge. Where multi-point locking systems
are used bolts may be omitted.
ACTION
When specifying door locks select the appropriate
lock(s) that provides the recommended lock functions
for the different dwelling types as stated above.
7

Standards
Extra
Cast stone to be recognised
in NHBC Standards
Over recent months NHBC has been considering how
cast stone can be recognised in NHBC Standards.
The 2008 revision of BS 1217 ‘Cast stone – specification’
includes architectural dressings such as heads, cills,
copings and string courses. It also includes cast stone
ashlar masonry.
The European Standard, BS EN 771-5 ‘Specification for
masonry units. manufactured stone masonry units,’
overlaps to cover cast stone ashlar masonry.
The term cast stone has been used and is the correct
description for reconstituted stone architectural dressings.
ACTION
The use of features made from cast stone
should comply with the latest version of BS 1217.
Better still, use the higher standards adopted by
UKCSA members (as previously recommended in
Standards Extra 36). Cast stone ashlar masonry
can also comply with BS EN 771-5.
QUESTIONS
Q
Slate hook fixings
Is it acceptable to use slate
hooks for fixing natural slates?
A
■
■
Roof fixings should be sufficient to resist the
wind uplift forces and avoid slates blowing off or
chattering on the roof. Fixings should also resist
lateral dislodgement of the slates.
Slate hook fixings come in two styles i.e. with a spike
end for driving into the tiling batten or a hook-over end
for hooking over a tiling batten. Both types are described
in BS 5534 ‘Code of practice for slating and tiling’.
Slate hooks
■ Slates are fixed with only one hook placed centrally
along the lower edge of the slate. NHBC Standards
clause 7.2 – S11(d) says slates should be fully nailed
over the whole roof.
No, the use of hook-over type slate hooks is not acceptable.
However, spike-ended slate hooks may be acceptable
providing they are minimum 2.7mm diameter stainless
steel wire and can be shown to resist the wind uplift for
the roof in question. The supplier should provide wind
uplift figures for the roof and his fixings to show
compliance, alternatively local examples of satisfactory
use of the hook fixings could be considered.
Slate hooks may be unsuitable for large slates which
experience a greater wind uplift than smaller slates
and for pitches above 75 degrees or below 25 degrees.
Slate hooks are available with straight or crimped shanks.
Crimped hooks reduce capillary action and should be
used for roof pitches below 30 degrees.
Slates at the perimeter of a roof e.g. eaves, valleys,
verges, ridges, hips, abutments and penetrations
should be nailed to resist uplift and lateral drift.
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
HB2467 12/08

Sustainability
Extra 3
December 2008
Osborne achieves Code Level 5
The Mid Street development in South Nutfield, Surrey,
is the first habitable Code for Sustainable Homes Level 5
affordable housing development in the UK. Built for the
Raven Housing Trust, perhaps the most striking thing about
these two flats is that, unlike most other homes built to high
levels of the Code, they have a very traditional appearance,
which hides the technology that lies under the skin.
Over the last few years Osborne has invested
considerably in developing the expertise needed to
face the challenges of sustainable homes. Its approach
is to consider sustainability from the inception of
the project. The Osborne Demonstration House at the
BRE Innovation Park was the first sustainable home
to be built on the site and the lessons learned from its
construction have been applied to Mid Street.
It is worth noting that a particular additional challenge was
that detailed planning consent had already been achieved
prior to the decision being made to build to Code Level 5.
Mid street development in South Nutfield
Energy and CO2 emissions
In order to achieve Level 5, close attention had to be
paid to all categories of the Code, but the biggest
challenges came from addressing the energy and
emissions targets. Carbon dioxide emissions needed to
be reduced by 100% and to achieve this, four guiding
principles were set for the design:
reducing energy demand
maximising passive solar gain
maximising the energy provided by renewable means
minimising the use of fossil fuel.
>>>

Sustainability
Extra
Reducing energy demand
A Structural Insulated Panel System
(SIPS) was chosen to construct the
walls of the homes. Wall panels
comprise a ‘sandwich’ of two layers
of 12mm oriented strand board and
150mm high performance expanded
polystyrene core. An additional layer
of high performance expanded
polystyrene insulation was provided
externally to deliver a U-value of
0.14W/m 2 K.
Sealing tapes were applied at panel
joints to control air leakage from the
homes. Air leakage testing on
completion confirmed extremely good
performance of just 1m 3 /(hrm 2 ).
Very high levels of thermal insulation
were provided to the roof and floor
and a mechanical ventilation system
with heat recovery was fitted in order
to minimise the amount of energy
lost due to exhaust ventilation.
Photovoltaic panels on used Mid street development
Maximising passive solar gain
The homes, which are orientated on the site to maximise
passive solar gain, are fitted throughout with highperformance
triple glazed windows. Window sizes were
optimised to maximise passive solar gain and provide
good levels of natural daylight inside the homes.
Maximising the energy provided by
renewable means and minimising the
use of fossil fuel
Space and hot water heating is provided by a shared
biomass boiler, which uses wood pellets as its fuel
source. There is a local supply of wood pellets and these
are delivered by tanker and stored in an external store.
The pellets are fed automatically to the boiler from the
store by an auger.
The boiler’s heat is stored in water in thermal stores
fitted in each flat and is distributed on demand by means
of an under floor heating system.
A large array of photovoltaic roof panels provides
electricity to the homes, and at times when the output
exceeds the homes’ demand, the excess is exported to
the National Grid. It is estimated that the array should
produce approximately 900KWh per year.
Water efficiency
Essential Code credits were obtained through the
installation of a rainwater harvesting system, which
filters and collects water from the roof in a large
underground storage tank. On demand, the stored
rainwater is pumped to tanks in the roof and is fed down
to supply WCs, washing machines and an outside tap.
Combined with water efficient appliances – shallow
baths, low flush WCs, aerated taps, plus digitally
controlled showers the estimated consumption of each
home will be 80 litres per person per day.
Costs
Osborne kept a close eye on costs at all stages of the
development. They estimate the additional total cost to
have been 24% (about £41,000 per home) compared with
equivalent homes built to current Building Regulations
standards. The highest expenditure items were:
Photovoltaic panels £19,000
Structural Insulated Panel System £12,800
High performance triple glazed windows £7,000
Rainwater harvesting system £6,500
(these are total extra-over costs for both homes)
Monitoring and feedback
The Energy Saving Trust will monitor the energy usage of
the Mid Street homes for a period of at least two years.
This will include heat output, water consumption and the
electricity generated from the photovoltaic roof panels.
Early feedback does suggest that there have been a few
teething problems as the residents get to grips with the
operation of the heating and mechanical ventilation
systems. Some technical problems have also been
encountered with the inverters (used to convert the DC
output from the photovoltaic panels into AC) tripping out.
2

NHBC Foundation
The NHBC Foundation’s latest reports cover
two important topics – the management of
construction site waste, and systemic failure in
house building.
‘Site waste management’ NF8
The management of onsite waste is becoming increasingly important to the
house-building industry. Not only is there a requirement to comply with
environmental legislation (including The Site Waste Management Plans
Regulations, which came into force in April 2008), but also to achieve cost
savings by implementing good environmental practice.
The construction industry uses an estimated 400 million tonnes of resources
every year with 100 million tonnes ending up as waste. Construction projects
involving multiple contractors can lead to confusion about who is responsible
for environmental issues with implications for management of waste and
disposal, licensing and permits, and working out who is responsible when
things go wrong.
In order to simplify the management of site waste, the NHBC Foundation and
the Waste and Resources Action Programme (WRAP) funded research carried
out by BRE to help the house-building industry write and implement site waste
management plans (SWMPs) and recognise the associated benefits of putting
these plans into practice.
This guide provides the findings of this research as well as information on
how waste created during the construction process can be managed more
effectively as a result of writing and implementing a SWMP. It also provides a
series of useful templates and checklists.
‘Learning the lessons from systemic building failures’ NF10
Throughout recent centuries there has been a gradual evolution of
house-building practice and a continuous cycle of innovation. From time
to time this innovation has inevitably given rise to unforeseen problems.
Solutions have been found for these problems, lessons have been learnt
and the industry has moved on.
In parallel with the continuous innovation, there has been continuous
refinement of building regulations, and our overall knowledge of what
constitutes good practice has also developed.
With innovative construction systems and materials, new detailing has to
be developed that allows the particular design to be built. In many cases
this leads to inadequate solutions, such as a reliance on sealants where,
for example, a properly detailed flashing might be more appropriate.
Although our overall knowledge has increased, it seems that our ability to
pass that knowledge on to successive generations of professionals has
diminished. This report reviews some historic problems for the benefit of
today’s generation of professionals. It focuses on a number of systemic
building failures that have come to light in various countries over the past
30 years, including:
failure of pre-cast reinforced concrete (PRC) houses in the UK
moisture penetration of external insulation finish systems (EIFS) in
British Columbia, Canada, the United States and New Zealand
failure of structural insulated panel (SIP) roof systems in Alaska, USA.
Site waste management report
Systemic failure in
house building report
ACTION
All NHBC Foundation
reports can be downloaded
at www.NHBCFoundation.org
(click on ‘Projects’ tab to
view all reports).
3

Sustainability
Extra
NEWS
Department of Energy and Climate Change
The new Department of Energy and Climate Change was created on 3 October 2008. Secretary
of State, Ed Miliband, has committed the UK to cutting greenhouse gas emissions by 80% on
1990 levels by 2050. In a wide-ranging Commons statement, Mr Miliband:
backed the recommendations of Lord Turner's Climate Change Committee and said the
Government would make the 80% reduction target binding in law by amending the Climate
Change Bill currently going through Parliament.
said that he plans to introduce a 'feed-in tariff' to support microgeneration and to make a
further announcement soon on encouraging renewable heat. The use of feed-in tariffs in other
countries, Germany in particular, has led to acceleration in the uptake of microgeneration.
Ed Miliband
Enhanced details
The Energy Saving Trust’s Enhanced Construction Details (ECDs) focus on the issue of
heat losses that occur at the junctions between building elements and around openings.
Designed to help the construction industry achieve performance standards that exceed
those set out in Building Regulations, they help developers and builders to meet the energy
requirements of the Code for Sustainable Homes.
Developed in association with an industry working group, these details improve on the
performance delivered by the standard Accredited Construction Details (ACDs) and allow
designers and builders to use a reduced thermal bridging y-value in SAP of 0.04 W/m 2 k.
Enhanced construction
details report
Further information is available in the Building Professionals section of the EST website at
www.energysavingtrust.org.uk/housing
New CLG research on costs and
benefits of zero carbon
‘Research to Assess the Costs and Benefits of the Government’s Proposals to Reduce the
Carbon Footprint of New Housing Development’ was published by CLG in September.
Commissioned from Cyril Sweet, Faber Maunsell and Europe Economics, it supports the
Regulatory Impact Assessment for the Building a Greener Future: Policy Statement published
in July 2007.
The report is an analysis of the costs and benefits of the proposed policy options for progressively
enhancing Building Regulations (by 25% in 2010, 44% in 2013 and zero carbon from 2016).
Zero carbon
research report
The report can be downloaded at:
http://www.communities.gov.uk/publications/planningandbuilding/housingcarbonfootprint
Review of the Code for Sustainable Homes
The latest amendments to the technical guide to the Code came into effect on 3 November
2008. The changes are generally minor in nature and correct or clarify the previous guidance.
A review of the Code has recently commenced. Led by consultants, Faber Maunsell, the review
will gather opinion on how the Code should evolve and NHBC will provide input to one or
more of the review workshops. Topics specifically under scrutiny include energy (in the light
of expected changes to Part L), the water calculator, ‘Lifetime Homes’ and adaptation to the
effects of climate change.
HB2450 12/08