Airtightness Testing

What you need to know?
This guide outlines the requirements of the approved Building Regulations for 2006 as they apply to new dwellings. The methodology of airtightness testing techniques is presented along with diagnostic methods such as smoke testing and thermographic surveys.

The 2002 Building Regulations required all commercial and industrial buildings with a gross floor area greater than 1000 m2 to be tested for airtightness to a minimum standard of 10 m3/(h.m2) at 50 Pascals (Pa). Not only does Approved Document Part L2A of the Building Regulations for 2006 extend this requirement to all sizes of commercial and industrial buildings, Approved Document Part L1A is also extended to include airtightness testing of new dwellings.

The Approved Document Part L1A for work in new dwellings will require, with few exceptions, type-testing of all new dwellings to an airtightness standard of no greater than 10 m3/(h.m2) at 50 Pa. For some dwellings where the carbon emission rate is difficult to meet for architectural reasons, then the airtightness target under the SAP calculations may need to be reduced to 7, 5 or even 3 m3/(h.m2) at 50 Pa to meet the overall carbon emission rate required by the Regulations.

Buildings containing rooms for residential purposes such as nursing homes, student accommodation and similar are not considered as dwellings. In such cases, Approved Document Part L2A will apply.

Building contractors who elect to adopt the accredited details route to demonstrating compliance with the Regulations will still be required to undertake airtightness testing, albeit with a potentially smaller sample of dwellings.

Who is this information aimed at?

Building Surveyors
To ensure new houses are sufficiently airtight, surveyors will need to specify the appropriate forms of construction as a matter of routine. By applying the BSRIA guidance, building surveyors will help to reduce building failures and save costs.

House Builders
The requirement for constructing low air-permeability dwellings is here to stay, and are likely to become more arduous in later editions of the Building Regulations. Housebuilders will need to adopt quality assurance regimes to ensure that air tightness testing becomes a routine task.

Testing Companies
The regulatory requirement to pressure test new dwellings creates a need for airtightness testing companies with the required level of calibrated equipment and personnel. In addition to this guidance, BSRIA can provide all the help
organisations require in terms of training, equipment, and instrument calibration.

Building Control
Building control officers will require test certificates from qualified testing organisations in order to fulfil their requirements under the Building Regulations. Testing organisations will also need to demonstrate ongoing competency.

How do I comply with the Building Regulations?

Uncontrolled ventilation in dwellings through leakage paths around doors and
window frames accounts for a significant proportion of heat loss, particularly as
the insulation values of walls and glazing has improved. In order to control this
energy loss, the Building Regulations will regulate the overall leakage of the
building structure by testing, using a pressurising/depressurising fan method.
This document specifically covers the methods used to comply with the
airtightness component of the Regulations.

Air permeability
This is the same standard of air tightness as introduced in Part L2 of the 2002
Building Regulations for buildings with a gross floor area exceeding 1000 m2.
Essentially, it is the amount of air required to pressurise and depressurise a
building to 50 Pascals (Pa), normalised with respect to the building’s envelope area.

Envelope area is defined as the area of the external walls, roof and footprint of
a building. A building’s footprint is usually defined by the area of the ground
floor slab, except where the building has a basement. The roof area is normally
defined as the area below the loft, where the loft is not an accommodation
area (in other words not conditioned). The area of external walls is only true
for detached properties. Semi-detached and terraced properties will have partywall
elements.

Quality of Construction
While the maximum allowable building air leakage rate is 10 m3/(h.m2) at 50 Pa,
designers may choose to create an even more airtight construction (7, 5 or even
3 m3/(h.m2) at 50 Pa) and to use the calculated energy saving to trade off
against other building details. It is likely that detached houses and bungalows
will have the greatest difficulty in meeting the Dwelling carbon dioxide
Emission Rate (DER), and will require a tighter air permeability specification.
The DER should be less than the Target carbon dioxide Emission Rate (TER).
Where U-values for elemental type, allowable areas of windows or doors, and
quoted efficiency of heating appliances do not (in total) enable the dwelling to
meet the required TER, then the target air permeability may need to be lower
than 10 m3/(h.m2) at 50 Pa.

Accredited and non-accredited construction details
Both routes to airtightness compliance will require airtightness testing of
samples of each dwelling type. For the purposes of Part L1, a dwelling type
means a dwelling of the same generic form:

Detached, semi-detached
End terrace, mid-terrace
Mid-floor, ground floor and top floor flats.

As different types of dwelling are not defined by their floor area, the number
of bedrooms will not necessarily define a particular building type. However,
different forms of wall or roof construction will be considered to define a
dwelling type. Where a housing development has a mix of construction forms,
it may require a higher number of air permeability tests.

The airtightness tests need to be carried out by an independent, qualified (or
accredited) person in accordance with the procedures set out in ATTMA
Technical Standard 1.

The pressure test value to be attained will be defined by the designer in the
SAP 2005 evaluation, but in any case will not be greater than 10 m3/(h.m2) as
this is the upper limit for air permeability set by the Building Regulations,
except for developments with two or fewer dwellings. Registration with the
British Institute of Non Destructive Testing (BINDT) with respect to
airtightness testing would be a demonstration that the testing organisation has
the appropriate skills.

Accredited Construction Details
On each development site, an air pressure test should be carried out on a
unit of each dwelling type selected by the building control body. A block of
flats should be treated as a separate development. On a particular site, one of
each type of dwelling from the first completed batch of units should be
tested to confirm the robustness of each design. A development will not
usually comprise many different types of dwellings, often less than ten.
However, achieving an air permeability of 10 m3/(h.m2) at 50 Pa should not
be an arduous task. This accredited construction detail route to airtightness
testing will probably be preferred by most building contractors, as it has the
potential to involve the fewest number of tests, although it may prove far more
expensive than airtightness testing. As the building control body will select the
dwellings to be tested, the builder must ensure that the quality of
construction is consistent.

Non-Accredited Construction Details
Paragraph 58 of the draft Building Regulations says that pre-completion pressure
testing will be required in accordance with the Table 1.

Table 1: The number of pressure tests for dwellings that have not adopted accredited construction details (from table 3, paragraph 58, of Approved Document L1A Conservation of Fuel and Power in New Dwellings).

Sample size
With respect to sample size, 50% of the required airtightness tests should be
carried out during construction of the first 25% of each dwelling type.
This is simply to demonstrate to the building control officer - as early as
possible in the building programme - that the buildings are complying with
the Regulations.

It would be prudent (for best practice) to test the first of each
dwelling type on each site in order to identify and modify any details that are
causing an airtightness problem.

Consequences of failing a pressure test
For the period up to 31 October 2007 the Regulations contain what is called a
“reasonable provision in the event that initial test results are unsatisfactory”.

This provision calls for remedial measures such that the result of a re-test shows:
an improvement of 75% of the difference between the initial test result and the target air permeability; or a test result no worse than 15% greater than the target air permeability.

As was the case for large commercial and industrial buildings in 2002, the
update to the Building Regulations for 2006 will include an 18-month
introductory period whereby the target air permeability will not be rigorously
applied.

For example, if the target value is set at 10 m3/(h.m2) at 50 Pa, and the first test
result was 16 m3/(h.m2) at 50 Pa or less, then a repeat test result of less than
11_5 m3/(h.m2) at 50 Pa will be deemed satisfactory. However, if the result of
the first test resulted in a value greater than 16 m3/(h.m2) at 50 Pa, the values
given in Table 2 would be required for the re-test.

Table 2: Pressure test failure and pass values.

Remedial measures
The Regulations stipulate that for each dwelling that fails the initial test,
remedial measures should be carried out as required by paragraph 61, and one
further dwelling scheduled for testing.

It is a reporting requirement that the independent testing company will know
the design target for the dwelling’s airtightness. It is the responsibility of the
building control officer to ensure that all the appropriate information relating
to the compliance of the Dwelling carbon dioxide Emission Rate (DER)
fulfills the requirements of the Building Regulations. However, in practice, it is
probable that the testing company will be in a position to advise the client on
the need for remedial works and re-testing requirements.

All pressure tests will be undertaken early in the build programme. If the
results are satisfactory to the extent that quality control for later buildings on a
development site can be relaxed, this will help to reduce the builder’s costs.

Exempted Areas
Note that where a conservatory is thermally separated from the new dwelling
it will be regarded as an extension. Rules for extensions are contained within
Part L1B which is for work in existing dwellings for which no airtightness
testing is required. The situation for garages is a little less clear, but if they are
not conditioned spaces, they would be outside the scope of the Regulations.

For expert advice on airtightness testing, call the BBS Sales Team today on
01928 579990 or alternatively e-mail sales@bbs-ltd.com.