Air tightness tests should be carried out at completion stage prior to handover. The results from the air permeability test are used within SAP software to produce the final as built EPC. 

Where a dwelling has been designed with a low air permeability target below 3 m³/hr.m² we would advise that a mid-build test is carried out once the air barrier layer has been installed. This allows early identification of any potential leaks and allows them to be sealed at source. A final test is still required at completion.