The passivhaus air tightness test standard (n50) is different from the building regulations standard (q50). The air tightness results for Passivhaus is calculated using the building's internal volume m3 rather than the building's envelop area m2.
It is recommended that the initial test should be carried out as soon as the air barrier is established but before building services are installed. This makes it possible to properly assess the the effectiveness of the air barrier.
The Pre-Completion Test is to be carried out after the building services are installed. This helps to determine any issues or further leakages that may have been introduced by the installation of the building services.
The final test is be carried out upon completion of the building and used for Passivhaus certification purposes. While the first two tests allow for identification and remediation of leakage issues, the final test confirms that the building conforms to Passivhaus Standards.