Air tightness testing is carried to check the air leakage that occurs from a buildings envelope. The air test checks amount of conditioned air that escapes or gets wasted through gaps or air leakage paths through the building fabric. If the building is more air tight, less energy will be being needlessly lost, thus lowering the carbon emissions of the building. Air tightness testing also shows how efficient a building is at retaining conditioned air which will also put less straight on your mechanical and ventilation system.
Failing to maintain adequate air tightness can lead to up to 50% of heat loss from within a building to the outside atmosphere. This negates the advantages of investing in energy efficiency measures such as extra insulation, high spec boilers or ground source heat pumps. Achieving an air tight building should be prioritised, otherwise your building will cost more to run and place extra load on your mechanical and electrical services; also, as if the building fails the air tightness test it may delay the handover of the building.
Air testing is mandatory in the United Kingdom and is governed by Part L of the Building Regulations, this split into two parts; for domestic properties Part L1A should be used and for commercial properties Part L2A should be referenced.