Airtightness testing procedures
When carrying out an airtightness test, a steady-state condition is established, when the air blown out of the building by the fan is balanced by the air re-entering the building through various cracks, gaps and openings. Typically this is at a pressure of 50 Pascals (Pa), about the same as a 20 mile-an-hour wind acting upon the volume under test, not forgetting that wind speed rises with distance above ground if testing in high-rise blocks.
Testing is carried out in the UK in conformance with the ATTMA (Air Tightness Testing & Measurement Association) 2010 editions of the standards TSL1 (dwellings) and TSL2 (non-dwellings). These are available as a free download from www.attma.org. A new scheme for quality control of testers was established on 1st January 2015.