Hello ,
at least as important as the correct determination of the n50 air change rate is the additionally recommended comprehensive differential pressure-supported leakage detection, combined with an exact documentation and evaluation of any identified defects regarding the resulting risk for the occurrence of later building damage.
Commissioning a suitable measurement service provider yourself largely ensures its independence.
An additional "advanced" leakage detection at the time when the airtight envelope is completed but the interior cladding is not yet installed would be optimal! Then the weak points identified by a leakage test could be professionally remedied immediately by the construction company!
Following this quality control, care must be taken to ensure that the airtightness layer is not reopened (perforated) by subsequent work.
For the final measurement, it is important that the determination of the heated building volume is done correctly on site. Using the value from the Energy Saving Ordinance verification is only conditionally permissible.
If only individual points of the outer shell are taped or otherwise additionally sealed for the measurement, this must be noted in the measurement protocol!
I am happy to answer any further questions!
Best regards from Erfurt
KPS