The most people have already heard about an air tightness test for dwellings but do not have a certain knowledge, to value the quality of the test and the results, they got.
Even the certified air tightness tester scheme here in Ireland, provided by NSAI, is (unfortunately) not a guarantee for a qualified and genuine air tightness test.
I´d like to point out some details subsequently, which are essential for a serious air tightness test:
1. Weather during the test
For an accurate test result it is important to have as less wind as possible during the air tightness test as well as almost similar temperatures between inside and outside.
2. Building dimensions
The air tightness tester has to double check the building dimensions on site, in case they got provided by a third party. An understandable calculation of the floor area, building volume and building envelope area should always be part of the test report.
3. Duration of an air tightness test
Coming from my experience, a formal test in compliance with the test standard (ISO 9972:2015) takes at least 2.5 hours for a (very small and straight forward) dwelling. Bigger houses with irregular shapes will extend the test. A two storey with 200m² can take up to 5 hours for a qualified air tightness test.
4. The right building phase for an air tightness test
The official test standard (ISO 9972:2015) allows two different tests - the preliminary and the final. The preliminary test is a quality control for the installed air tightness layers and should be performed right after the installation work, to allow adjustments and improvements. The final test has to be done when the house is finished. Finished means nothing else than the majority of construction works is finished and the house is more or less ready to move in. If the house is not finished, the test can´t be declared as a final test.
5. Detection of existing leakages during the test
Surprisingly, not every (NSAI certified) air tightness tester is performing a leakage detection prior to the official depressurization & pressurization test. It´s clearly stated in paragraph 5.3.1 of the ISO 9972:2015, that such check of the building envelope is mandatory and detailed notes have to be taken about detected leakages.
6. Range of building pressures for an air tightness test
Many air tightness test reports come with the required quantity of induced pressure differences but the most of them have just readings for higher differential pressures. The air tightness test standard is clearly setting the lowest limit for the data collection in paragraph 5.3.4: "The lowest pressure difference shall be approximately (i.e. with an allowance of ±3Pa) 10 Pa or five times the value of the zero-flow pressure difference(ΔP01), whichever is greater."
It´s more difficult and time consuming to measure at lower pressure differences, that´s why some testers do finish their air tightness readings always at around 20-30 Pa differential pressure.
There´s plenty of options to manipulate an air tightness test, wittingly or unwittingly. It starts with wrong building dimensions and ends in manipulating the fan. I do not want to provide details of how to manipulate an air tightness test, because every air tightness test is a formal procedure. There´s no advantage of having a better air tightness test result in the report than in reality.
8. Official standard for air tightness testing
Here in Ireland, the mandatory standard for air tightness testing is
"I.S. EN ISO 9972:2015 - Thermal performance of buildings - Determination of air permeability of buildings - Fan pressurization method". The previous European norm EN 13829 for air tightness testing is not longer valid for formal testing.
If you´re in need of an air tightness test or in case you might have doubts about details of an existing test, please feel free to get in contact with me, to discuss how you can be supported.