Air pressure tests are the mandatory method by which developers measure the air tightness of their residential developments. Testing shows how well properties will retain heat and in turn reduce carbon emissions, making them more efficient and cheaper to maintain. Air pressure testing is a legal requirement of part 'L' of the Building Regulations 2006. 

The testing involves raising the air pressure inside the property by 50 Pascals (a very small increase in air pressure) using a large fan inserted in the entrance doorway. The rate by which the internal air pressure returns to normal is then measured which indicates how airtight the building is. This has a major effect on the thermal performance of the property. The result from the APT is incorporated in the final SAP calculation and production of the EPC for the property. 

All residential new buildings and commercial buildings require testing.

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