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TM23 Revision

Revision of Testing buildings for air leakage (TM23): January 2021 update

In 2019-20, as part of its consultation on Part L, Part F and the Future Homes Standard, MHCLG sought views on whether low-pressure pulse testing should become an approved methodology for airtightness testing of new dwellings for Building Regulations purposes. To accompany this, CIBSE produced a draft revised TM23 for consultation, which contained a section on low-pressure pulse testing alongside other methods of airtightness testing.

MHCLG has now announced that low-pressure pulse tests will become an approved methodology. CIBSE will revise TM23 accordingly, so that the relevant section of TM23 can be referenced in the Building Regulations and associated guidance.

We have reviewed comments received as part of the 2019-20 consultation and are now in the process of producing a revised draft. In the meantime, the 2019 draft is provided here for reference: TM23 Consultation FINAL 15 10 2019. Please note this will change significantly in response to the feedback we received last year.

If you provided comments on the previous draft, you do not need to provide them again. However, do contact us if you would like to provide new additional information which would contribute to the evidence base supporting the methodology.

Background to the 2019-2020 consultation

CIBSE TM23 was first published in 2000. At that time there was a proposal that air-tightness testing be introduced into the building regulations in England and Wales (Wales at that time not having its own regulations). There was an International Standard for the test method, but it dated from 1976.

The 2002 revisions to Part L introduced air tightness testing into the Approved Documents as a way of establishing the performance of buildings. That guidance referred to CIBSE TM23 as a source of the test method. However, it was not until 2006 that Regulation 43 of the Building Regulations was introduced to require air tightness testing. Regulation 43 also recognised a competent persons’ scheme for air tightness testing. By this time a British and European Standard had been adopted.

Today, airtightness is usually tested by the blower door method at a pressure differential of 50Pa, generally by a competent person belonging to one of two approved schemes. They follow the methodology which evolved from TM23 and is now published by one of the schemes, although there is now a British, European and International Standard for airtightness testing, BS EN ISO 9972-2015.

In recent years an additional test method to supplement the blower door test has been developed and evaluated for field use. The low pressure pulse test applies a pressure pulse to the building envelope and measures the pressure response in the building volume following the release of the pressure pulse. It dynamically measures building air leakage directly at a lower pressure differential of 4Pa, which is more representative of conditions that properties are likely to experience.

As part of the package of proposals presented with the Government consultation The Future Homes Standard: changes to Part L and Part F of the Building Regulations for new dwellings it is proposed that the test methodology should be published independently of the approved schemes, and that the low pressure pulse method should also be included in the test method publication and recognised by government.
The MHCLG consultation seeks views on introducing the Pulse test as an approved method of airtightness testing for new dwellings with a designed airtightness of between 1.5 m3/m2.h and the maximum allowable airtightness value.

To ensure that the approved methodology for airtightness testing is independent of all organisations with an associated competent person scheme, Government proposes approving an airtightness testing methodology written by the Chartered Institution of Building Services Engineers (CIBSE).