GUIDANCE | TM23 The latest update to the Building Regulations includes reference to a new CIBSE TM23 guide on airtightness testing. Julie Godefroy reviews the new TM, which includes a new approved air testing methodology, and considers the impact of the changes TIGHTENING UP A substantial revision of TM23 Testing buildings for air leakage was published in January 2022, prompted by two important changes introduced in the update to Building Regulations in December 2021, which come into force on 15 June 2022. The Approved Documents now refer to CIBSE TM23, rather than the Air Tightness Testing & Measurement Association (ATTMA) standards, as approved methodology for air leakage testing. A revision to TM23 was, therefore, needed to reflect the significant advances and standardisation in the fan pressurisation (blower door) method that have occurred since the original publication of TM23 in 2000. A second testing method, the low-pressure pulse (LPP, or Pulse) technique, is now approved by the Department for Levelling Up, Housing and Communities for testing new-build homes, alongside the blower door technique. These developments are part of a number DEFINITIONS Inltration is used to refer to air movement through the envelope under normal conditions. Air leakage is used to refer to air movement through the envelope under a pressure differential. It is expressed as air leakage rate at a reference pressure, either as air change rate or air permeability. Left: The revised version of TM23, released in January of recent advances in building performance evaluation, which include the use of smart meters for estimates of heat transfer coefficients1 and the new BS 40101 on in-use building performance evaluation. To improve the design and performance of buildings, it is essential that we carry out much more testing, says David Allinson, from the Building Energy Research Group, School of Architecture, Building and Civil Engineering at Loughborough University, who is one of the peer-reviewers of the TM. Measuring air leakage is one important and cost-effective approach. So, it is fantastic to see CIBSE providing updated guidance in this fast-moving and exciting area of research and innovation. Testing techniques The fan pressurisation technique, developed in the 1980s and used throughout the world, uses a fan (or series of fans) to pressurise or depressurise a building; the air leakage rate is derived at a reference pressure, which is 50Pa in the UK. There are a number of standards available to cover the technique and associated calibration requirements, and a reasonable track record on repeatability of results. As the building is under (de)pressure conditions, it is possible to carry out leak-finding during the test for example, using smoke pens. The reference pressure of 50Pa is higher than buildings experience in normal conditions and, as such, the technique is viewed as a stress test. Consequently, there has long been interest in developing a test that would be more representative of the pressure conditions usually experienced in buildings. While tracer-gas methods directly measure 26 April 2022 www.cibsejournal.com CIBSE Apr 22 pp26-28 TM23.indd 26 25/03/2022 17:35