What is an Airtightness test?
An airtightness test (also known as a door blower test) is a way of measuring the leakage in a building and is a great way of checking the quality of design, detailing and site work. Tests are mandatory in all new builds as part of the building regulations although the levels of leakage allowed are many times greater than those in a passive house. Details of design and testing are outlined in this document from the Passivhaus Trust.
How is an air test undertaken?
A door blower fan is fitted into a door or window opening and the pressure reduced to negative pressure of 50 Pascal inside the building. Any leaks can then be detected and remedied before the final tests are made.
The air change rate must be less than or equal to 0.6 air changes per hour, under test conditions. Normally the building is tested with both negative 50 Pascal and positive 50 Pascal and an average taken. This then evens out any leakage from either inward or outward opening doors and windows.
It should be noted that it is much harder and sometimes nearly impossible to fix leaks towards the end of the build. A clear plan for airtightness needs to be made during the design stage, and then have someone on site responsible for ensuring all trades comply during the build.
Testing my build
My test was carried out by Merlin Consultants and was pretty un-dramatic straight forward affair. The test engineer quickly set-up the door blower and set about reducing the pressure in the building. Straight away it was clear there was very little air leakage. There was a slight whistling noise and movement of air around a couple of the key holes but no air could be detected leaking anywhere else. The good level of airtightness was also confirmed whilst testing with a positive pressure in the build. The tester commented that it was very unusual to have such a leak free build without Passive rated windows as non Passive windows tend to leak slightly on either one of the negative or positive pressure tests.
Air test results
I knew the results were going to be pretty good when the tester said that it was the best result he had ever had. After a few minutes of measuring the internal volume of the build and some calculations I was very pleased to recieve a result of 0.33 air changes an hour at 50 Pascals, a significant improvement over the limit of 0.6 required to achieve a Passivhaus rating.