June 2010 - NHBC Home

NHBC’s technical newsletter
Standards
47
Extra
June 2010
This edition includes:
When does timber decking
become a balcony?
New soil guideline values
Eurocodes
Three new Approved Documents
Keeping concrete in its place

Standards
Extra
CONTENTS
1
Balconies/raised
timber decking
2
Glassfibre reinforced
concrete
3
Eurocodes
4
Plasterboard
cracking
5
New ADs
When does timber
decking become a
balcony?
In response to some recent enquiries, it seems that
clarification is required on when timber can be used for the
primary structure of raised timber decking and why it’s not
permitted for balconies.
Raised timber decking is dealt with in Chapter 9.2 of the
Standards, whereas ‘Flat roofs and balconies’ are dealt with
in Chapter 7.1.
6
B/Regs in Scotland
8
Seals and sealants
8
MCS and BBA certs
for renewables
9
Soil guideline values
10
Clean cover systems
11
Keeping concrete in
its place
12
Questions and
Answers
Raised timber decking
Where any part of the decking is going
to be more than 600mm above ground
level the design and construction
should be carried out in accordance
with the guidance published by the
Timber Decking Association (TDA).
Their guidance does allow timber to be
used provided it is correctly detailed
and, where required, preservative
treated. No part of the decking should
be more than a storey height (e.g.
2.40m) above ground level, and access
ACTION
to the decking comes from rooms on
the ground floor.
Balconies
A balcony is a structure that provides
an external area at first floor level or
above. As such, and resulting from
previous problems, NHBC considers
that the use of timber, as the primary
structure, is not appropriate.
If in doubt, please refer to NHBC
Standards and Technical for further
advice technical@nhbc.co.uk.
If you are going to build either raised timber decking or an external
balcony into your design please ensure that you use the correct
materials. Particularly note that timber is not permitted as the
primary structure in balcony construction.
2

Issue 47
June 2010
Glassfibre Reinforced Concrete (GRC)
GRC was first introduced in the early 1970s and is now used on some of the world’s largest
and most prestigious building projects. In the UK, use of the material by house builders and
developers is growing, both as a cladding solution and as a lightweight and durable alternative
to traditional cast stone dressings.
It is essential that GRC is correctly
designed and manufactured for its
intended purpose with appropriate
quality control procedures in place.
GRC is a cement-based composite,
reinforced with special alkali resistant
glass fibres, which are blended
throughout the concrete matrix to
give a material which displays a high
resistance to tensile, bending and
impact forces.
GRC products may typically be only
12-15mm thick, formed using thin wall
casting or spraying techniques. The
weight of GRC products is considerably
less that than their conventional
counterparts which helps with handling
and installation. The nature of the
material provides good resistance to
damage at edges and corners.
Traditional concrete is classified by
its compressive strength (i.e. C40),
GRC is classified by reference to
its characteristic flexural strength
(termed in the industry as Modulus
of Rupture or MOR). For convenience
of specification, GRC is graded into
three categories, Grade 8, Grade 10,
and Grade 18, each grade representing
numerically the characteristic MOR
value. Correct GRC manufacture
requires that a regular testing regime
is operated to measure and record
MOR values (and other parameters)
on a continuous basis.
GRC in the UK will typically be
manufactured in accordance with the
best practices developed in Europe,
America, Asia and Australasia over
the last forty years. The International
Glass Reinforced Concrete Association
‘Specification for the manufacture,
curing and testing of GRC products,
Third Edition – March 2010’ is an
important reference for ensuring good
quality GRC. This is consistent with,
and refers to, national standards BS
EN 1169 and BS EN 1170: 1998 parts
1-7. A copy of the specification may
be downloaded from the websites
ACTION
of the GRCA (http://www.grca.org.
uk/technical/downloads.asp) or the
Concrete Society.
To ensure satisfactory in-service
performance products must be
designed to ensure adequate strength
and appropriate fixing. The test data
obtained from regular test results of a
manufacturer is essential in validating
the values used in design. This is
particularly important for built-in items
such as heads and band courses or the
larger cladding panels which may be
formed in GRC.
When selecting a GRC product the user
must ensure that design will be carried
out in accordance with the relevant
national standards for any intended
profile or panel form, including the
design of the fixing systems used to
support or restrain GRC items. It is
equally important to ensure that the
manufacturer has access to both the
facilities and procedures to carry out
the testing required in the manufacture
of GRC, or alternatively has in place
arrangements for third party testing.
The Glass Reinforced Concrete
Association operates an ‘Approved
Manufacturers Scheme’ whereby
participating companies have
demonstrated to the Association
they have the procedures, plant and
equipment to comply with the required
specifications and standards. For
further details about the GRCA and
its Approved Manufacturers Scheme
please visit www.grca.org.uk
If you are proposing to use GRC products make sure they have been
designed and manufactured in accordance with recognised standards
and that the manufacturer is a member of the GRCA scheme.
3

Standards
Extra
Eurocodes
The Eurocodes are here and conflicting BS Codes have now been withdrawn.
Eurocodes have become the national
standards for structural design
Structural Engineers in Europe are
facing the greatest ever change in
design codes and standards as the ten
Eurocodes for structural design are
implemented. In the UK all 58 Parts
together with their National Annexes
are published and many familiar British
Standards have been withdrawn. Under
an agreement between the European
standardisation bodies conflicting
national structural design standards
had to be withdrawn by 31 March 2010.
The Eurocodes are published by BSI as
BS EN 1990 to BS EN 1999 and they are
now our national standards.
When is the changeover to the new
standards?
There is no fixed date and it will be
a matter of choice for designers and
their clients. However, the adoption
of Eurocodes will initially be driven by
EU directives on public procurement
enacted in the UK as the Public
Contracts Regulations 2006. These
Regulations will require most UK
public sector organisations, utilities
and product manufacturers to adopt
Eurocodes as the preferred basis
for defining technical specifications
and designs. BSI will no longer be
maintaining or updating the old British
Standards, which are expected to fade
from common use over the next few
years. Reference to the Eurocodes will
be updated as the Building Regulations
Approved Documents are revised. In the
case of Approved Documents A and C,
the next periodic review has started and
new versions are expected in 2013.
In a letter to Building Control Bodies
(BCBs), which can be found at http://
www.communities.gov.uk/documents/
planningandbuilding/pdf/1454859.pdf,
the Department for Communities and
Local Government has stated; “When
assessing compliance with the Building
Regulations, BCBs should continue to
consider the appropriate use of relevant
standards on a case by case basis.
BCBs will need to be aware of the risk
of designs inappropriately mixing new
design standards based on the BS ENs
and withdrawn BS design standards.”
To help you meet changing design
requirements, NHBC Building Control can
accept designs to either the old British
or new European codes to support
proposals to satisfy Building Control
and NHBC Buildmark submissions, but
not a combination of both. Whether
using the old or new codes, designers
should satisfy themselves, and NHBC
Building Control, that the designs are
still relevant to the particular design
requirements of each project.
For further information visit
www.nhbc.co.uk/bc
ACTION
European codes and standards
on site
In recent years European product
standards have replaced many familiar
BS standards. The new standards
are more performance based, which
provides designers with greater choice
and scope for innovation. Similarly, the
new design standards also offer greater
scope for innovation. This means that
project specification drawings and
details will often need to state the
required performance characteristics
(e.g. strength, density, fire resistance,
thermal conductivity, water absorption)
and on site it will become more
important to check that the products
used are the correct ones with the
required performance characteristics.
Where products bear the CE marking,
the required performance values, levels
or classes will be available on a label,
on the packaging or in accompanying
documentation.
With the introduction of the Eurocodes as the new National Standards
and the withdrawal of the old British Standards, designers will need to
satisfy themselves and NHBC Building Control that the appropriate use
of relevant standards has been adopted. This will need to be considered
on a project by project basis.
4

Issue 47
June 2010
Have you heard the one about plasterboard ceilings
making a cracking noise?
This is no joke, but along with a number of house builders, NHBC has become aware that under certain circumstances
a cracking noise appears to come from plasterboard ceilings. Ceilings can be to floors or the underside of a roof void.
Although this sounds trivial, homeowners who have experienced the problem are not laughing. It is annoying to say
the least and because it can happen during the night it can break sleep patterns and generate associated problems.
As far as we are aware the number of such incidents is very small but we would like to know about as many as possible.
This can then be fed into the work that has already been done to try to understand where and why it happens.
If you have had the problem we would like to hear from you. Please contact NHBC Standards and Technical on
0844 633 1000 or by email technical@nhbc.co.uk
Three new Approved Documents
Three new Approved Documents have recently been published and this article explains
what has changed and the implications for house builders. All three become operative
from 1 October 2010, and will apply to works from this date, unless work has already
started on site, or a formal application is submitted prior to this date, with the
requirement that works start on site before 1 October 2011.
Part L 2010 – Conservation of
fuel and power
Introduction
The new Part L 2010 brings with it
the next step towards the challenge
of zero carbon homes. Structured to
deliver a 25% improvement in thermal
performance and energy efficiency
on the outgoing 2006 document,
similar to current Code Level 3 energy
performance requirements for new
dwellings, the changes will bring
significant challenges particularly for
developments including flats.
The following headline issues address
the principle changes and assess
the implications for developments to
meet the new Approved Document
requirements.
5

Standards
Extra
Regulation Changes
It is now a requirement to submit
Target CO 2
emission rates (TER),
Dwelling/Building CO 2
emission rates
(DER/BER) for the building, and a list of
specifications used in the calculations
to the Building Control Body before
works start on site.
Main Changes
So what are the implications of the
recommendations contained within
Part L 2010, and how will they impact
on the design and construction phases?
1. Air permeability andpressure
testing
Essentially the amount of on-site
testing is likely to at least double.
Either three units or 50% of each
dwelling type should be tested on each
site, whichever is the lesser. Blocks of
flats are treated as separate sites, even
if there are multiple blocks within the
same development.
The specific dwellings to make up the
test sample should be selected by the
Building Control Body in consultation
with the appointed pressure testing
body. Early appointment of the testing
body could be beneficial here.
The other significant change is the
relevant information to include in
the DER calculation. Where pressure
tested, this specific figure should be
used. For non-tested dwellings, the
DER figure should be the average
test results achieved for the same
dwelling type +2.0m 3 /(h.m 2 ) at 50Pa.
This in basic terms means that design
air permeability will be nearer 8.0m 3 /
(h.m 2 ) to achieve compliance with the
maximum value of 10.0.
2. Requirement to submit information
With the introduction of Regulation
20D, it is now a requirement to
submit TER and DER information
and calculations in full, including the
specifications used to achieve the
design CO 2
emissions, to the Building
Control Body prior to works starting
on site.
The current requirement to submit
DER achieved alongside the TER
information, together with information
pertaining to changes in specifications
to reflect the as-built dwelling, within
five days of completion remains.
An EPC is also required for all new
dwellings and non-domestic buildings.
3. Improved limiting U-values
New limiting U-values have been
introduced for the building fabric,
and are as follows:
External Walls 0.3 W/m 2 .K
Roofs 0.2 W/m 2 .K
Party Walls 0.2 W/m 2 .K
Floors 0.25 W/m 2 .K
Windows 2.0 W/m 2 .K
A significant change for Part L 2010 is
the notional dwelling used for the TER
assumes a party wall U-value of 0.0
W/m 2 .K. The above limiting U-values
require inclusion of party walls in the
overall fabric insulation calculation.
In reality cavity party walls will
require some insulation, although
of course all current robust details
for acoustic performance show clear
cavities to prevent sound transfer. The
implications here are currently being
reviewed, and we should be able to
provide more detailed guidance in
due course.
4. SAP 2009
Thermal bridges – effective U-values
should now be based on the length
of each junction and the relevant psi
values from SAP 2009. An alternative is
to use a relevant approved government
accredited construction detail scheme,
although details of such schemes are
not yet available, so initially SAP 2009
will be the option together with on-site
checks during construction.
Energy efficient light fittings – at
least 75% of light fittings must be low
energy, determined by the Domestic
Building Services Compliance Guide.
Providing more than 75% low energy
lighting provision will help toward the
DER calculation.
Secondary heating – the default penalty
has been removed and is now based on
the actual secondary heating provided,
with the exception of dwellings with a
chimney but no appliance installed, in
which case there is no change from the
current default penalty.
A preview of SAP 2009 can be viewed
from www.nesltd.co.uk website.
5. Shell and Core developments
There is clearer guidance on the
construction of shell and core units,
whether stand alone or part of mixed
use developments. The developer
should show by the design stage
TER/BER calculations how the building
shell could meet energy efficiency
requirements.
Where certain systems are not
installed, the BER will have to assume
efficiencies for those services that
will be installed as part of the first
fit out work, and these figures and
assumptions in full must be provided to
the Building Control Body before the
works start.
Part F 2010 – Ventilation
Introduction
Part F 2010 includes significant
revisions to align with the changes
made in Part L, ensuring minimum
energy efficiency levels for all
ventilation systems.
The use of trickle ventilation looks
set to become more difficult, with
additional guidance published for
dwellings with design stage air
permeability tighter than 5.0m 3 /(h.m 2 ),
meaning approximately 50% more
background ventilation is required for
dwellings with intermittent or passive
stack ventilation systems.
This could prompt designers and
builders to move towards continuous
ventilation systems, which are better
performing in SAP 2009, as well as
simpler to standardise. Continuous
ventilation systems do not require
trickle vents either, which could be a
significant advantage.
6

Sustainability 7
Extra
June 2010
Miller Zero
Miller Zero is the name given to a collection of five homes on a development
of 79 units in Basingstoke, Hampshire. Although almost identical in
appearance and layout, the homes have been built to five different levels
of the Code for Sustainable Homes. For private sale, the homes will allow
Miller Homes to understand the challenges of designing, building and
marketing homes built to meet the Code at increasing levels and satisfy
increasingly stringent energy standards of building regulations.
Construction
The homes have been built using a variety of different
construction methods, including thin joint cavity
masonry, SIPS (structural insulated panel system) and
a storey-height aircrete panel system. With 200mm of
external wall insulation, the Code Level 6 aircrete panel
house achieves a wall U-value of 0.09W/m 2 K; the use of
wet plaster in this home enabled an extremely low air
permeability figure of 1.48 m 3 /m 2 /hr to be achieved.
The ground floor construction for each of the homes
accommodates approximately 100mm of insulation,
although the type of material used varies.
In the case of the Level 6 home the use of urethane
insulation together with the reinforced aircrete planks
achieves a floor U-value of 0.11W/m 2 K. Rigid urethane
is used to insulate the roofs and in the Level 6 home,
a thickness of 190mm is supplemented by a 52mm
insulated plasterboard lining, which gives an overall
U-value of 0.12W/m 2 K.
At the lower Code Levels, double glazed low-e units
have been installed in PVC-U frames to achieve an
overall U-value of 1.7W/m 2 K. But for the Level 6 home
triple glazing was required and this reduced the overall
U-value down to 0.68W/m 2 K.
continued >>>

Sustainability
Extra
The Code Level 6 aircrete panel house under construction
Heating systems
Selected to meet the energy/CO 2
targets of the different
Levels of the Code, a variety of systems have been
installed at Miller Zero:
• The 10% reduction in CO 2
emissions required at
Code Level 1 was achieved with a conventional gas
condensing boiler and radiators.
• For Level 3 (25% CO 2
reduction), an air source heat
pump used in conjunction with radiators was selected.
• For Level 4 (44% CO 2
reduction), a ground source
heat pump connected to an underfloor heating
system was used.
• For the Level 5 (100% CO 2
reduction) and Level 6
(zero carbon) homes, the solution chosen was a
biomass boiler. Fuelled by wood pellets, a single boiler
shared between the two homes is located in
an adjacent garage.
Ventilation
All of the homes have been built with high standards
of air permeability in mind and, in order to ensure that
this does not give rise to poor indoor air quality or high
humidity levels (and associated risks of condensation
and mould growth), mechanical ventilation systems have
been specified for all five homes.
The equipment is located in the first floor airing cupboard
to reduce duct lengths and incorporates heat recovery
to minimise the amount of heat lost from the outgoing
exhaust ventilation air. The units also feature a summer
by-pass option for the warmer months of the year.
Renewables
The planning application included a small-scale wind
turbine, located in a communal area. However, whilst the
local authority was supportive of the development in
general, approval for the turbine was not granted.
Other than the biomass boiler serving the Level 5 and
6 homes, the only other renewable technology installed
was photovoltaic panels. The monopitch roof of the Level
5 home accommodates panels with an area of 14m 2 ,
whilst the Level 6 home has 38m 2 of panels – well over
twice the size. The peak output from the PV installations
is 1.7kW and 4.8kW respectively.
Non-energy/CO 2
Code challenges
A variety of other features have been specified to satisfy
the other elements of the Code. These include water
efficient fittings and appliances, rainwater harvesting,
many storey-height windows to maximise daylighting
levels as well as providing space for recycling, etc. Great
attention has been paid to detailed design, specification
and construction on site to pick up required number of
points in all categories.
Lessons learned
This project has already given Miller Homes an
invaluable insight into the challenges of designing and
building homes to meet the increasing demands of the
Code and future changes to thermal requirements of
building regulations. The exercise also demonstrated
the significant additional costs involved, amounting to
incremental increase as higher levels of the code are
achieved up to £50,000 for the Code Level 6 unit.
Subject to permission being given by the owners, built-in
sensors will be used to monitor the performance of the
homes in use for a 12-month period, during which, the
reaction of the occupants to the variety of technologies
installed will also be recorded. The owners will also be
able to closely monitor their own current consumption
of energy using ‘smart meters’ that have been provided.
The biomass boiler for the
Code Levels 5 and 6 houses
The air source heat pump of the Code Level 3 house
A mechanical ventilation with heat
recovery unit above the hot water cylinder
2

Sustainability
Extra
Homebuilding skills
Understanding the skills and knowledge needed for delivery of
zero carbon homes
The transition to zero carbon will require
huge changes in the way we plan, design,
build and live in new homes. Achieving
this important transition successfully
will depend on how well the industry is
supported, and a foremost challenge
will be to ensure that the house-building
sector is equipped with the right skills
and knowledge.
But, for the professions and trades,
what core skills will be needed and what
knowledge must be acquired to ensure
that we can build to zero carbon
standards from 2016?
The Homebuilding Skills Partnership
In mid-2009, the Zero Carbon Hub established a Skills
and Training Workstream to provide a forum for debate
on future skills and training needs. This Workstream
rapidly evolved into a partnership body between NHBC,
Construction Skills and the Zero Carbon Hub. This
partnership, called Homebuilding Skills is uniquely
positioned to understand the complexity of the zero
carbon challenge and the practicalities of building homes
and delivering training programmes. It set itself the
following objectives:
• To develop a Home Building Skills Action Plan for
the UK.
• To identify the specific skills and knowledge needed
to deliver low and zero carbon homes.
• To support the industry in raising the standards in
homebuilding.
• To identify complementary action needed (by those
other than home builders).
Progress – developing the Skills Action
Plan to 2020
Though the exact definition of a zero carbon home is not
yet finalised, there is a growing understanding of what
must be achieved in practice. Key steps in delivery are
now mapped out chronologically by the Zero Carbon
Hub on its timelines which are used to monitor progress
to full delivery against zero carbon standards. A major
workshop last November gave deeper insights into
the ‘operational scenarios’ which will prevail at the
key staging points together with the broad, associated
training needs.
That preliminary position was set out for industry
consideration as an on-line consultation, which aimed
to capture specific training objectives and needs. Each
major homebuilding activity, including Building Control
and inspection, was given an opportunity to comment.
The feedback from the consultation will be collated
and key findings reported back to the industry and
government policy advisors later this year. The report
is expected to trigger wider debate, but in its final form
it will provide the evidence to steer the overall Home
building Skills Action Plan.
3

Sustainability
Extra
Why it’s important
The importance and urgency of this work is
well-described by Alastair Collin of Construction
Skills who sets out the complexity of the challenge –
“Many companies are unable to articulate what they
specifically need but definitely know their needs are
changing. This means that training providers and
assessment centres are also unable to determine
specific needs and develop tailored solutions in
response – this work will help clarify needs and
inform the skills and training response.”
Imtiaz Faroohki (NHBC’s Chief Executive) sees the
work as helping to unite the industry in defining and
confronting the skills gap – something that is going
to be crucial in meeting tough post-recession output
and sustainability targets for housing, while Neil
Jefferson of the Zero Carbon Hub sees the work as
vital in ensuring that national training is linked to
the excellent progress already made by the industry.
These strategic considerations are all reflected in
the approach taken by Homebuilding Skills and its
consultative, inclusive approach.
Future flexibility
There’s a busy year ahead to draw up skills and
knowledge matrices for each major profession and
trade. In some cases it may be a simple extension
of existing skills or knowledge. In other situations,
crucial new skills or knowledge may be identified.
The Zero Carbon Hub will be able to feed in new
information to inform training requirements as the
year proceeds, particularly on delivering the 70%
carbon compliance level for new homes. One thing is
certain – the need for the matrices to be responsive
to change and future policy clarifications. For
example, though it could not be defined today, we can
anticipate a major training programme surrounding
how to deliver ‘Allowable Solutions’ – the new part of
the definition of zero carbon homes which is under
policy development at this time. In contrast it is quite
possible to envisage a logical programme of training
to support the now well-developed area of Fabric
Energy Efficiency.
The findings from the consultation exercise will be
developed into an online hub, which all those involved
in homebuilding (whether site managers, architects,
bricklayers or others) will be able to use to establish
what training support they need, and where to find it.
For general information on this work please visit
http://www.homebuilding-skills.com. If you have any
queries please contact: Rob Lockey, NHBC Training
Services Manager. rlockey@nhbc.co.uk.
4

Sustainability
Extra
NHBC Foundation
Set up in 2006, the NHBC Foundation has now completed 25 projects, outputs from
which are published on its website at www.NHBCFoundation.org. The latest two
reports improve our understanding of the efficient use of piled foundations and
consider how the performance of drainage systems may be affected if, in future,
the volume of water used to flush WCs is further reduced.
Efficient design of
piled foundations for
low-rise housing:
Design guide
Amongst the benefits of
using piled foundations are
a range of environmental
advantages that may help
achieve compliance with
the Code for Sustainable Homes.
Although the advantages will depend upon the
particular development site and the type of piling
selected, they can include:
• reduced waste arisings and less waste to landfill
• reduced neighbour nuisance – vibration, noise and
air quality
• reduced embodied carbon dioxide emissions due
to the reduced volume of concrete used.
In addition to these potential advantages, it is
sometimes even possible for the collector loop of a
ground source heat pump to be enclosed within piles.
This NHBC Foundation report, prepared with support
from Arup, considers these environmental aspects
alongside other key considerations relating to the
selection and efficient design of piled foundations.
This project undertaken by WRc, with support from
the Foundation and other research partners, studied
the potential consequences of lower flush volumes on
the performance of drainage systems. Test rigs were
used to identify the how far various solids would travel
along a drainage system before coming to a halt as the
amount of water used for flushing was reduced.
The principal finding of the project was that the
current combination of typical flush volumes
together with typical drainage system layouts does
provide satisfactory performance. However, if the
flush volume is reduced and/or the length of the
drain is increased, performance is reduced and
could potentially become unsatisfactory, leading
to increased problems with blockages. This project
provides useful data, which will be used to inform
further debate on related standards and regulations.
‘Pull the chain, fill
the drain’
Improvements to the water
efficiency of new homes are
increasingly being driven by
the Code for Sustainable
Homes and also (in England
and Wales) through Part G
of the Building Regulations.
One key component of
domestic water consumption
is that used for flushing WCs, and significant
quantities of water can be saved by specifying WCs
with lower flush volumes.
The drainage test rig
5

Sustainability
Extra
NEWS
The Code for Sustainable
Homes: Case studies
Three years on from the introduction of the Code for
Sustainable Homes, the Department for Communities
and Local Government (CLG) has published its second
volume of case studies showing examples of five
developments designed and built to comply with the
Code. The examples cover a range of development
types built in both the private and affordable sectors
to achieve between Code Levels 3 and 6, using
various construction methods.
The case studies summarise builders’ experience
of working with the Code. Amongst the comments
included is that “unsurprisingly, those projects that
planned to build Code homes from the outset found
it easier to meet the requirements rather than
adapt homes that had been designed to a different
standard, as there are significant differences between
the Code and previous standards” – a useful tip for
builders who have yet to confront the challenges of
the Code.
The document is available for free download from:
http://www.communities.gov.uk/publications/
planningandbuilding/codecasestudiesvol2
Code for Sustainable
Homes: A cost review
This review published by
CLG in March updates
the Impact Assessment
produced in November 2007
that analysed the costs and
benefits of introducing Code
ratings on a mandatory
basis.
This study considers the
extra-over cost of building to
the Code above constructing
homes to comply with
building regulations. Four dwelling types were
modelled, combined in a variety of ways (in terms
of number of dwellings, dwelling mix and dwelling
density) to create development scenarios and cost
data were obtained through a direct consultation with
the house-building industry.
The overall finding is that there is significant
variation in the extra-over costs at each Level of
the Code between the dwelling types and across the
development scenarios. Typically, however, the
extra-over costs expressed as a percentage of base
build cost are:
Code Level
Extra-over cost
1 Less than 1%
2 1-2%
3 3-4%
4 6-8%
5 25-30%
6 30-40%
The report is available from the CLG website at:
http://www.communities.gov.uk/publications/
planningandbuilding/codecostreview
HB2503 06/10

Issue 47
June 2010
Regulations changes
A new requirement to Part F means
that where possible, fixed mechanical
ventilation systems require testing and
commissioning. In addition, for both
intermittent and continuous mechanical
ventilation installations, air flow should
be measured. This would include cooker
hoods for kitchens and extract fans to
bathrooms.
Details of this data must then be sent
to the Building Control Body within
five days of completion, adding another
procedure to follow at the completion
stage.
It is also a requirement to hand over
sufficient information to the building
owner in relation to the systems
installed in a new dwelling.
Main changes
As mentioned above the most
significant change is to dwellings
with air permeability of less than
5.0m 3 /(h.m 2 ).
By choosing a continuous mechanical
extract system, Part F 2010 now
removes the need for background
ventilation in dwellings designed with
air permeability rates above 5.0m 3 /
(h.m 2 ). There are also benefits in SAP
2009 for continuous systems, which
may lead designers to adopt whole
house mechanical extract ventilation
systems, possibly including heat
recovery as well, which would maximise
the SAP benefits.
If using passive stack ventilation,
internal pipes should now be sized at
125mm diameter serving all spaces,
an increase from the Part F 2006
requirements.
Published alongside the new
regulations is the Domestic Building
Services Compliance Guide, in which a
new requirement for specific fan power
of less than 0.5 watt/sec applies for
intermittent extract fans.
ACTION
Part J 2010 – Combustion
appliances and fuel storage
systems
Introduction
There are a number of changes in
the new Part J 2010 beyond those
relevant to the new requirements
of Part L 2010, the most significant
change is the requirement for carbon
monoxide alarms in dwellings with fixed
combustion appliances.
There is new guidance on protection to
oil tanks, external vertical flues, access
to concealed flues and additional
ventilation requirements for open
flued appliances in dwellings with air
permeability of less than 5.0m 3 /(h.m 2 ).
Main Changes
There is now a requirement to provide
a carbon monoxide alarm to dwellings
with a fixed combustion appliance,
although the Approved Document
guidance applies only to solid fuel and
biofuel appliances. An alarm should
be sited between 1m and 3m of an
appliance, and be provided with a
suitable long term power supply.
There is guidance on the provision of
access to concealed flues/chimneys.
Inspection hatches should be at least
300mm x 300mm, the number and
location must be sufficient to allow
visual inspection of the flue/chimney
system, and check that:
• The flue/chimney is continuous
throughout its length
• Joints are correctly assembled
and sealed
• The flue/chimney is adequately
supported throughout its length, and
• Any required gradient or drain
points for condensate are provided.
Flues should be designed not to pass
through other dwellings, and access
If you would like to find out more about the changes or would like to
talk about a new project please contact 0844 6331000 and ask for
‘Building Control’ / ‘Colin Blatchford-Brown’, or visit our website
www.nhbc.co.uk/bc
should not adversely affect fire,
thermal or acoustic provisions.
To link in with the requirements in
Part L 2010, for dwellings with air
permeability of less than 5.0m 3 /
(h.m 2 ), there are additional ventilation
requirements for open flued appliances.
For example an appliance with a
rated output up to 50kW should have
850mm 2 /kW of permanent ventilation
for this level of air permeability as
opposed to 550mm 2 /kW for more
leaky dwellings.
Another consideration within Part
J 2010, is the potential requirement
to provide additional containment
protection to oil tanks up to 3500
litres for new dwelling. If a new
dwelling is located within Zone 1 of
the Environment Agency Groundwater
Source Protection Zone (SPZ), then
secondary containment is required to
the oil tank. Further information on the
mapping can be found at
www.environment-agency.gov.uk/
research/library/maps.
And finally there is now clarification on
the recommended flue outlet position
for external vertical flues fixed to an
outside wall, essentially to comply as if
it were a normal chimney or flue above
a pitched roof.
…and building regulation changes
in Scotland
In April the Scottish Government
published the 2010 edition of
the Technical Handbooks. The
amendments to the Scottish
building regulations come into
force on 1 October 2010. The
handbooks can be downloaded
from the Scottish Government
website (http://www.scotland.gov.
uk/Topics/Built-Environment/
Building/Building-standards/
publications/pubtech).
Alternatively hard copies can be
purchased from The Stationery
Office (TSO).
7

Standards
Extra
Perimeter sealing of doors
and windows
In this article we look at the perimeter sealing of windows,
doors, other openings and interfaces. The three key factors
that will ensure maximum performance and durability of the
installation are weathertightness, airtightness and insulation.
All of these must be fully considered at design stage.
How is a good quality airtight
seal achieved?
By using a membrane capable of
accommodating movement (i.e. it
has to be flexible) after installation.
Proprietary products are available with
inbuilt flexible folds for movements and
pre-applied adhesive strips to bond
the membrane to the window
and structure.
How is an external
weathertight seal achieved?
Whilst good quality silicone and other
wet sealants may provide adequate
performance, the use of impregnated
foam tapes also provide (at a minimum
of 600 Pascals)
good long term life
expectancy as well as
the ability to cope with
significant movement
and wide joint size
tolerance. Impregnated
foam also offers
breathability allowing
any moisture behind the
seal to dissipate to the
exterior of the building.
A range of quality
sealants are available
and installation should
be carried out in
ACTION
accordance with the BASA (British
Adhesive and Sealants Association)
Industry Guide to Professional
Application of Construction Sealants
on Site.
How can the thermal
performance of the window
frame/structure connection
be enhanced?
Gun applied air tight PU foams are
available with high levels of movement
accommodation. However, enhanced
impregnated foams have been
developed that provide the three
required levels of sealing (airtightness,
weathertightness and insulation) in
one application.
Ensure that appropriate seals and sealants are correctly specified and
installed to achieve maximum in-service performance.
ACTION
Microgeneration
Certification Scheme (MCS)
publishes guide for installers
Towards the end of April MCS
published a guide entitled ‘Low
and zero carbon technologies:
opportunities and the MCS’.
The guide is for installers of
renewable energy systems on the
MCS quality assurance scheme.
The guide is available as a free
download from http://www.
microgenerationcertification.org/
docs/Opportunities-and-the-MCS_
web.pdf.
BBA issues certificates for
renewable energy systems
Earlier in the year the British Board
of Agrément issued its first two
MCS Certificates. These were the
result of a certification process
set out in the Microgeneration
Certification Scheme (MCS). The
two products are:
• Clearline Solar Collector from
Viridian Solar (Certificate 0001)
• TopSola TSM-160M Solar
Photovoltaic Modules from MAP
Environmental (Certificate 0002)
NHBC will soon be looking
for renewable energy
system products and their
installation to be covered
by the MCS scheme. If
your house designs are
incorporating renewable
energy systems or you
have an installer who is
not currently covered by
MCS and would like to know
more then please pass this
information on.
8

Issue 47
June 2010
Contaminated Land - New Soil Guideline Values
Soil Guideline Values (SGV’s) were
originally introduced by DEFRA
in March 2002 for a range of
contaminants that may be found in
the ground on brownfield land or
previously developed sites. The SGV’s
were specifically developed for use
in assessing the risk to human health
from contamination in soils as part
of the Contaminated Land Exposure
Assessment (CLEA) framework for
use in the UK.
The CLEA framework and SGV’s were
developed to provide authoritative
guidance in support of the
implementation of Part 2A of the
Environmental Protection Act 1990
that laid down the new regulatory
role for Local Authorities dealing
with land contaminated and also to
provide a more robust and scientific
method of assessment to replace
the previous guidance: 1987 ICRCL
(Interdepartmental Committee on
the Redevelopment of Contaminated
Land) recommendations for action and
trigger levels for contaminants in soils.
However, since the original publication
in 2002 further detailed scientific
reviews together with extensive
consultations with stakeholders in
the contaminated land industry have
resulted in a number of fundamental
revisions to the contaminated land
framework and the model known as
CLEA UK used to produce SGV’s.
As a result, in July 2008, the 2002
SGV’s were withdrawn as they no
longer reflected the updated UK
approach to human health risk
assessments.
From late spring 2009, new SGV’s
have been produced and published
for a variety of contaminants using an
updated framework and model now
known as CLEA 1.06. These revised
SGV’s are recognised in the UK as
being authoritative and scientific. They
should be used as a tool to aid the
evaluation of whether a concentration
of a contaminant in near surface soils is
‘acceptable’ in the assessment of long
term risks to human health for various
land uses including residential.
SGV’s are intended only to assess
long term risks to human health from
contaminants in soils and they do not
take into account other issues such as:
• Risks for short term exposure
• Other types of risk to humans, such
as fire, suffocation and explosion
• Non-human receptors, for instance
ecological, controlled waters,
property, domestic produce or
domestic pets
• Contaminant sources arising from
and to controlled waters (ground
water)
• Free phase products in soils or
groundwater beneath the site (e.g.
hydrocarbons such as oils, diesel,
petrol).
DEFRA has an ongoing programme
for publishing SGV’s for potential
contaminants in soils and during
2009 values have been released
for the following; Benzene, Toluene,
Ethylbenzane, Xylene (Hydrocarbon),
ACTION
Mercury, Selenium, Arsenic, Nickel,
Phenol, Cadmium and Dioxin’s including
PCB’s.
When assessing contamination
on a site, representative site soil
concentrations at or below an SGV
indicate that it is unlikely that there
is a significant possibility of harm
to human health and the site can be
considered safe for development. When
concentrations exceed an SGV, there
may be a potential risk to human health
and further risk assessment is required
to determine whether remediation is
necessary.
Due to the complex nature of contamination, it is recommended by
the NHBC that a suitably qualified person/consultant should always
be used to investigate the site, assess the risks and develop any
remediation strategy as necessary.
9

Standards
Extra
Contaminated land –
Cover system validation
Introduction
Clean cover systems (also known as
‘simple capping systems’, ‘capping’
or ‘covering’ amongst others)
are frequently used methods
of remediating contamination
encountered on brownfield sites.
Their simplicity means that they are
often highly effective in ensuring that
the future occupants of residential
developments won’t be affected by any
contamination that remains on the site.
Background
Clean cover systems predominantly
involve placing an appropriate
thickness of suitable subsoil and/or
topsoil over areas of a site affected
by contamination. They work best
when the contaminants present are
low to moderate concentrations of
heavy metals or similar substances (i.e.
arsenic, lead). They are not appropriate
when high levels of contamination that
pose a significant risk to human health
are present, nor when petrol, other
hydrocarbons, asbestos, a high water
table or potential flooding are present.
In order to identify whether a cover
system is appropriate for a site, it is
essential that the nature and extent
of the contamination present has
been fully investigated by a suitably
experienced consultant or specialist.
Capping and topsoil validation
Where a clean cover system is adopted
to remediate a contaminated site,
the successful completion of the
remediation works will need to be
proven (‘validated’) by a suitably
experienced consultant or specialist.
Two of the major aspects requiring
consideration during validation are:
Photographic record of trial hole
1. Confirmation that the designed
thickness of the material has been
placed.
2. Confirmation that the materials
comprising the cover system are not
in themselves contaminated.
The requirements for validation are
outlined in NHBC Standards Chapter
4.1 ‘Land Quality – Managing Ground
Conditions’. NHBC requires that
the works are managed under the
supervision of suitable consultant or
specialist and we are provided with a
validation report before the homes
are finalled.
Further guidance on validation can also
be found in BRE 465 ‘Cover systems for
land regeneration – thickness of cover
systems for contaminated land’.
Validation of thickness
The thickness of the cover system is
typically validated by digging trial holes
in treated areas once the cover system
has been placed. Alternatively, on some
sites it may be convenient to use data
from level surveys made before and
after cover system placement from
which the thickness of cover materials
can be calculated.
Where trial holes are used to confirm
the cover thickness, the validation
report should clearly state the
locations and numbers of the trial
holes. Confirmation of the thickness
of the cover can be evidenced by a log
describing the materials encountered in
the trial holes and/or by photographs of
the trial holes with a tape or staff clearly
showing the hole depth. Placing a piece
of wood or similar flat item (clipboard
etc) at the ground surface immediately
adjacent to the tape/staff can make it
easier to indicate the depth.
Chemical testing
Chemical analysis of capping material
used on contaminated sites is essential
to demonstrate that the materials
are not themselves contaminated
and are suitable for their intended
use. The analysis should consist of
an appropriate set of tests for the
presence of possible contaminants.
This may be undertaken in several
ways by:
1. Using soils (including manufactured
soils) from a commercial provider
who can provide the results of
quality testing conducted ‘at source’
and who can confirm that the
materials delivered to the site are
representative of those tested. Any
test certification from suppliers
should be current and representative
of the material actually being used
on site.
2. Identifying a suitable source
of material on site or at other
construction sites (i.e. perhaps
generated from excavation
activities) and testing this prior
to incorporation into the works
or importation to the sitebeing
remediated.
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Issue 47
June 2010
3. Obtaining and testing samples of
soils once they have been placed if
no independent testing certification
is available.
Where separate subsoil and topsoil
materials are present in the cover
system, it will be necessary to confirm
the chemical quality of both of these
components.
Though British Standard BS3882:2007
contains details of sampling and
chemical testing that can be undertaken
to determine the characteristics of
topsoil, this is primarily aimed at
assessing its suitability as a growth
medium. Separate chemical testing is
normally required for any contaminants
that may be present posing possible
risks to human health (e.g. heavy
metals, hydrocarbons) and these need
to be provided to NHBC as part of the
validation.
The specific requirements for chemical
testing should ideally be discussed and
confirmed with a suitably experienced
consultant or specialist. Remember
that chemical testing of soils can take
up to two weeks to complete. Finalling
of a plot cannot be done until this
testing has been completed.
Where soils are tested off-site and are
confirmed as being suitable (i.e. where
they come from a commercial provider
Trial hole depth from ground level
or another site), it will be necessary
to provide NHBC with delivery notes
confirming that the tested and
accepted materials have been delivered
to the site.
Testing frequency
It is important that testing of the cover
system is conducted at a sufficient rate
to give adequate confidence regarding
the depth and quality of the material
used for the remediation.
ACTION
This will depend on a number of
factors, such as number of plots
being constructed and the source of
the material being used, but current
practice across the industry suggests
that for sites with more than 30 plots
testing should be conducted at a rate
of one plot in four, for sites with more
than 20 and up to 30 plots the testing
rate should be one plot in three, for
sites with between 5 and 20 plots one
plot in two should be tested, and where
fewer than five plots are being built it
will be necessary to provide validation
testing for every plot. In addition, for
sites with fewer than three plots it may
be necessary to conduct more than one
test per plot, in order to ensure that
an adequate number of samples are
tested. Again, advice should be always
sought from a suitable consultant or
specialist and NHBC staff are available
to discuss and agree acceptable testing
regimes at the early stages of any
project.
Ensure that you are aware of the requirements of NHBC Standards
Chapter 4.1 and that proposals for validating cover systems are
agreed with NHBC. Also ensure that sufficient time is allowed before
finalling to conduct chemical testing, the preparation, submission and
assessment of the validation report.
Keeping
concrete
in its place
Foundations in shrinkable soils (e.g.
clays), which will be affected by the
removal of trees, need protection from
clay heave.
Piled foundations are often used in
these situations, as they perform much
better, and can often be cheaper, than
deep trench fill foundations.
In order to protect the reinforced
concrete ground beams from the upward
and lateral swelling heave pressures
of the clay as it increases its moisture
content, heave protection materials
such as low density polystyrenes or void
formers must be used.
Placed along the side and under the
beams, the low density polystyrene or
void formers compress and absorb the
pressures, thus preventing damage to
the beams. If damage were to occur
to the ground beams it could in turn
damage the walls and floors above.
However, it has become evident
from a number of expensive claims
over recent years that void formers
and compressible materials are not
working effectively because of poor
workmanship in their installation.
Wet concrete grout can easily ‘leak’ from
poorly fitting void formers or sheets of
compressible materials when ground
beams are poured. This grout can fill the
voids in a void former and thus make it
ineffective when heave occurs.
Small gaps of 5-10mm, where two
sheets of compressible material abut
can, under a head of 500mm concrete,
allow voids to fill over a substantial
length of beam. The beam then has no
heave protection, and the heave forces
are transmitted to the building. This
causes extensive damage, which is very
expensive to repair.
11

Standards
Extra
Void formers are often placed in the
bottoms of trenches, without shuttering
above for the beam. So gaps down the
sides of void formers allow grout in. A
grout liner of polythene, placed around
the beam, will prevent this. Corrugated
plastic sheets are even better, in a ‘U’
shape to seal around the sides and
bottom of the beams.
NHBC inspectors also report that
gaps can often be found where the
square edges of the void former meets
the circular pile. Unless the gap is
properly filled with a void former, heave
problems will also occur here.
Pile collars made from 1m long blocks
of polystyrene with a hole cut to fit
tight around the pile, or corrugated
plastic sheets placed on top of the void
former, are recommended for sealing
tight around the piles, and preventing
grout loss.
ACTION
It is important that wet concrete grout from ground beams is retained
and does not fill voids that are there to accommodate clay heave.
QUESTIONS
Q
Are slip ties required across movement joints in
masonry cladding to timber frame walls?
A
NHBC Standards clause 6.1 - S5(c) says at movement joints,
wall ties should be spaced at maximum 300mm centres
vertically within 225mm of the joints on both sides of the
joint. The ties provide lateral restraint to the unrestrained
ends of the masonry wall. Similar guidance is given in
clause 6.2 - D6(b). Wall ties should be fixed to timber studs.
The spacing of the studs is often more than 225mm from
the movement joint. The addition of extra studs, within
225mm of the movement joint, may be impractical. Slip
ties, inserted across the movement joint, can be used to
tie the end of the wall in place of additional wall ties within
225mm of the movement joint.
The need for and provision of slip ties across movement
joints should be decided in accordance with the following
diagram:
• Where W and X are not more than 225mm (i.e. Y =
maximum 450mm centres) no slip tie is required. Wall
ties both sides of the movement joint should be spaced
at maximum 300mm vertical centres.
• Where W or X are greater than 225mm slip ties
should be built in across the movement joint at
maximum 300mm vertical centres. Slip ties should be
de-bonded at one end e.g. with plastic cover sleeve,
with minimum 50mm embedment into masonry either
side of the movement joint.
NHBC Standards and Technical
NHBC House, Davy Avenue, Knowlhill, Milton Keynes, Bucks MK5 8FP
Tel: 0844 633 1000 Fax: 0844 633 0022 www.nhbc.co.uk Email: technical@nhbc.co.uk
12
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