Section 7: Air permeability and pressure testing

7.1 The minimum standard for air permeability of a new building is given in Table 4.1 of Section 4.

7.2 The building control body should be provided with evidence that test equipment has been calibrated using a UKAS-accredited facility or by the original manufacturer within either of the following periods.

a. The previous 12 months.

b. A period in accordance with manufacturer’s guidance.

Calibration should be carried out in accordance with CIBSE’s TM23. It is recommended that test equipment is recalibrated at least every 24 months.

7.3 Building control bodies may accept a pressure test certificate as evidence that the building complies with regulation 43 of the Building Regulations.

The building control body should be provided with evidence that the person who pressure-tested the building meets both of the following.

a. Has received appropriate training.

b. Is registered to test the specific class of building.

7.4 Buildings that are not dwellings, including extensions that are being treated as new buildings to comply with Part L, must be pressure tested except those types listed in paragraph 7.5.

7.5 The following buildings do not need to undergo pressure testing.

a. Buildings with less than 500m2 total useful floor area. In this case the developer may avoid a pressure test, provided that the air permeability used to calculate the building primary energy rate and building emission rate is taken as 15m3/(h·m2) at 50Pa.

b. A factory-made modular building that meets the following criteria:

i. the floor area is less than 500m2

ii. the building has a planned service life of more than two years, where the intended time of use in a single location is less than two years

iii. no site assembly work is needed other than linking standard modules using standard link details.

If the building as installed conforms to a standard configuration of modules and link details for which the installer has pressure test data, this test data may be used to estimate the air permeability. Test data must be from a minimum of five in-situ measurements of the same module types and link details as used in the actual building. Air permeability should be in m3/(h·m2) at 50Pa. When calculating the building primary energy rate and building emission rate for
a factory-made modular building as described above, the value that should be used for design air permeability is the average air permeability test result at 50Pa plus 1.0m3/(h·m2).

c. Large extensions. If the building control body agrees that sealing off and testing the extension separately from the existing building is impractical, the extension should be treated as a large, complex building – see paragraph 7.5d.

d. Large complex buildings. If pressure testing is impractical due to the size or complexity of the building, the developer may produce both of the following.

i. A detailed justification of why pressure testing is impractical.

ii. A detailed strategy to give confidence that a continuous air barrier will be achieved.

It is reasonable for the building control body to accept this strategy in place of a pressure test to assess compliance.

The developer should seek expert advice to confirm the justification and strategy in paragraph 7.5d. Any justification and strategy should be in line with the approved airtightness testing methodology, CIBSE’s TM23. It would not be reasonable to claim that air permeability better than 5.0m3/(h.m2) at 50Pa had been achieved.

e. Compartmentalised buildings. If buildings are compartmentalised into self-contained units with no internal connections, it is reasonable for the building control body to accept a pressure test carried out on a representative area of the building as evidence of the building’s air permeability.

If the area of the building fails the test, the criteria in paragraphs 7.1 and 7.6 apply, but the developer should also carry out a further test on another representative area to confirm that all parts of the building achieve the expected standard.

Showing compliance and reporting pressure test results

7.6 The building primary energy rate and building emission rate calculated using the measured air permeability must not be higher than the target primary energy rate and target emission rate, respectively.

7.7 If the criteria in paragraphs 7.1 and 7.6 are not achieved, the building air permeability should be improved. New tests should be carried out until the building achieves the criteria in paragraphs 7.1 and 7.6.

7.8 The results of all pressure tests on buildings, including any test failures, should be reported to the building control body.

Air pressure testing procedure

7.9 Air pressure tests should be performed following the guidance in the approved airtightness testing methodology, CIBSE’s TM23. The procedures in that document have been approved by the Secretary of State.