The only way to check the quality of the airtight construction envelope is to carry out a pressurisation test using a Blower Door device. In this test, a negative or positive pressure is created in the building in question and the leakage rate measured. From this leakage rate V50 [m³/h] the v50 value [m³/(h.m²)] can then be calculated for the EPB report and the n50 value [h-1] for the PhPP calculation. It is best not to wait until the building is completely finished before carrying out the only and definitive test because it is often very difficult or impossible to repair airtightness leaks at that point. It is better to carry out a preliminary, exploratory test a number of times during construction so that any airtightness leaks can immediately be detected and repaired. Such a preliminary test could, for example, be scheduled for the following times: