When we set out on this adventure we decided that we wanted to achieve PassivHaus Certification. It’s absolutely possible to build a passive house without going through the certification process, and it is equally possible to simply incorporate passive house concepts and approaches into a “standard build”. In fact, in a future blog post I plan to share my musings on the various ways of going passive.
To get certification we have to prove that the house complies with the standards, which are:
- Space heating demand does not exceed 15 kWh annually OR 10 W (peak demand) per square metre of useable living space
- Space cooling demand roughly matches the heat demand with an additional, climate dependent allowance for dehumidification
- Renewable primary energy demand not to exceed 60 kWh annually for all domestic applications (heating, cooling, hot water, and domestic electricity) per square metre of usable living space
- Airtightness of a maximum of 0.6 air changes per hour at 50 Pascals pressure (as verified with an onsite pressure test in both pressurised and depressurised states)
- Thermal comfort must be met for all living areas year-round with not more than 10% of the hours in any given year over 25 degrees C
To demonstrate that we meet requirement #4 we ran a blower door test. We did this before the walls were lined so that if the results showed a penetration had occurred, we would be able to find and fix it with minimal effort. When building an airtight home, regardless of whether certification is being sought, it’s probably a really good idea to run a blower door test anyway as it can provide reassurance that the airtightness has been achieved.
The blower door is a pretty special piece of kit. It’s basically an adjustable screen that is inserted into a doorway. The screen has a fan/blower incorporated into it and is wired up to a computer monitor.
All doors and windows are closed and the computer drives the fan to pressurise and depressurise according to the preset parameters defined in the computer system.
The critical point is 50 Pascals of pressurisation which is the point where the number of air changes is tested. The volume of the house is calculated and this is used as the base measurement for comparison against the amount of air the blower door calculates is being “leaked” during a timed period. Averages across the pressurised and depressurised values are calculated with a final average being the test result.
We had to be at or below 0.6 air changes per hour and our result came in at 0.49. We were elated!
The blower door test is repeated right at the end of the build process when all finishing trades have completed their work so that we can be confident that no airtight membrane penetrations have occurred during the completion phase.