Some Frequently Asked Questions on Air Tightness Testing

What is Air tightness testing? Air tightness testing is the measurement of uncontrolled air leakage from a building.

How is an air test carried out? A blower fan is fitted to an external doorway, all internal doors opened and windows closed and the building pressurised (or depressurised), usually to 50 Pascals. It’s a light pressure difference only, but enough to allow the accurate measurement of air leakage. Design ventilation is closed and sometimes sealed, but no other temporary sealing work should be undertaken – the purpose of the test is to assess these unintended areas of air leakage!

When and why is the air tightness test required? the test should be carried out only once the building is completed. It is required as part of final sign off for building control compliance, and to provide an as-built input to final SAPs and SBEM Calculations.

How is the air permeability calculated? The Air Permeability figure is the level of leakage from the building in m3 per hour, divided by the envelope size in m2. So an envelope of 250 m², with a leakage air flow of 2,500 m3/h would give an air permeability of 10.0 m³/h/ m². It differs from Air Changes per Hour (ACH), in that the ACH is based on internal volume (m³) rather than envelope (m²).

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