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CIBSE TM23 Buildings Air Leakage Test Revision

The CIBSE TM23 air tightness testing document has been revised, with a draft for consultation now available for review.

Revised CIBSE TM23 for Air Leakage Testing

The TM23 was first published in 2000, and was introduced into Part L of the Approved Documents in 2002, as a method of determining building air leakage performance.

However, air tightness testing did not become a requirement until 2006, when it was stipulated in Regulation 43 of the Building Regulations. At the same time, Regulation 43 introduced a competent persons’ scheme for air leakage testing.

Low pressure pulse method

The revised TM23 will recommend the inclusion of the ‘low pressure pulse’ method – to supplement the long-established ‘blower door’ method.

As part of a range of proposals published with the government consultation “The Future Homes Standard: changes to Part L and Part F of the Building Regulations for new dwellings”, it is recommended that the test methodology be published separately to the approved schemes. It is also proposed that the new pulse method be part of the test method document and accepted and recognised by the government.

Blower door method

At present, the ‘blower door method’ is most commonly used to measure air tightness testing, at a pressure differential of 50 Pa, and is carried out by a competent person who’s a member of an approved scheme.

However, in recent years the pulse method has become used as a supplementary technique, and has been developed and evaluated for use on-site. The process involves applying a pressure pulse to the building envelope, and measuring the building volume’s pressure response following the pressure pulse. It uses a considerably lower pressure differential of 4 Pa, which more closely mirrors real-world conditions.

The MHCLG consultation aims for the pulse test to be introduced and used for airtightness testing for new buildings with a designed airtightness of between 1.5 m3/m2.h and the highest permitted airtightness value.

The government proposes approving the air leakage test method developed and published by the Chartered Institution of Building Services Engineers (CIBSE), so the final approved methodology is independent of all organisations connected to a competent persons scheme.

Part L, Part F consultation

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

iATS Registered and UKAS Recognised


We are registered with iATS (Independent AirTightness Testing Scheme) and use equipment calibrated by UKAS laboratories. Our testing procedures are also recognised by UKAS.