DHAPT - Domestic House Air Permeability and Pressure Testing

Approved Document L1A

Conservation of fuel and power

QUALITY OF CONSTRUCTION AND COMMISSIONING

L1A

56 The approved circumstances under which the

Secretary of State requires pressure testing to be

carried out are set out in paragraphs 57 to 63.

This means that if a design adopted a low design

air permeability in order to achieve a performance

better than the TER, it would not fail to comply

with Part L if the pressure test achieved the limit

value and the TER was achieved.

Dwellings that have adopted

approved construction details

57 On each development, an air pressure test

should be carried out on a unit of each dwelling

type selected by the BCB. For the purposes

of this Approved Document, a block of flats

should be treated as a separate development

irrespective of the number of blocks on the site.

The dwelling(s) to be tested should be taken

from the first completed batch of units of each

dwelling type.

Most larger developments will include many

dwelling types – and one of each type should be

tested to confirm the robustness of the designs

and the construction procedures.

Dwellings that have NOT adopted

approved construction details

58 Air pressure tests should be carried out on

each dwelling type in the development to the

number specified in Table 4. For the purposes of

this Approved Document, a block of flats should

be treated as a separate development

irrespective of the number of blocks on the site.

Table 4

Number of pressure tests for dwellings that have not adopted accredited

construction details

Number of instances of the dwelling type

Number of tests to be carried out on the dwelling type

4 or less

One test of each dwelling type

Greater than 4, but equal or less than 40

Two tests of each dwelling type

More than 40

At least 5% of the dwelling type, unless the first 5

units of the type that are tested achieve the design air

permeability, when the sampling frequency can be

subsequently reduced to 2%

59 The specific dwellings making up the test

sample may be selected by the BCB in consultation

with the builder. They should be selected so

that about half of the scheduled tests for each

dwelling type are carried out during construction

of the first 25% of each dwelling type.

The aim is to enable lessons to be learned and

adjustments to design and/or site procedures made

before the majority of the dwellings are built.

Consequences of failing

a pressure test

60 Compliance with the requirements would be

demonstrated if:

a. the measured air permeability is not worse

than the limit value set out in paragraph 37; and

b. the DER calculated using the measured air

permeability is not worse than the TER.

This means that if a design adopted a low design

air permeability in order to achieve a performance

better than the TER, it would not fail Part L if the

pressure test achieved the limit value and the

TER was achieved.

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