Skip to content

Revising CIBSE TM23 – Testing Buildings for Air Leakage

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 50 Pa, 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 4 Pa, 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).

This revised draft of TM23 has been produced in response to this, and it contains a section on the Pulse methodology alongside other methods of airtightness testing. If the Pulse method is accepted as an approved method, then the relevant section of TM23 will be referenced in the Building Regulations and associated guidance. CIBSE is therefore consulting on the proposed revisions to TM23. We are inviting comment on the draft and welcome constructive suggestions that seek to improve the draft.

The draft to be commented on is available for download here:
CIBSE TM23 - Draft for Consultation - October 2019

Comments should be made using the CIBSE Consultation Comment Form, available for download below, and send to

The draft is open for comment until 10 January 2020, which is the closing date for the consultation on Part L, Part F and the proposed Future Homes Standard.