At ATSPACE, we can air test a building if it is empty or occupied. There is no requirement to have the building empty for an air tightness test. Having said that buildings are usually empty when tested, as it makes leakage detection easier if there are any issues with the test.
Most builders will plan the air test in the program of works before the property is handed over to a client or occupation. The building should be tested as soon as it is complete, as all the final finish has been completed and the best chance of a successful result is possible. Once the property becomes occupied and lived in, the fabric of the building will change.
You can seek help from your assessor right from the design stage. The design of a building plays a huge part in how air tight it will be. Your building, once constructed, will settle and breathe. Shrinkage will develop around seals and floors. By using the heating and ventilation, the air flow in the building will form its natural paths of leakage.
Talk to ATSPACE for more Air Tightness questions.