Airtightness Testing: Some Interesting Results
As Passivhaus specialists it’s no surprise that we are passionate about airtightness. It’s vital to achieving Passivhaus certification but more importantly a draught free home is comfortable and more economic to run.
Airtightness is just a technical measure of how draughty a building is, how much air leaks out through unplanned holes and cracks. It is measured in terms of leakage from the building at a set pressure (50 pascal), then divided by the surface area of the building, expressed over a period of time. So, for example building regulation (Part L1A) requires a maximum air permeability of 10m3/hr/m2 Simple put this means that 10m3 of air can escape from your home every hour for every m2 of your home. As the warm air leaves the new colder air will be felt as a cold draft until it is warmed.
Yes, introducing fresh air into the building is important but this should be undertaken in a planned way. In a Passivhaus this would be through a MVHR unit to take the stale air out of bathrooms and the kitchen introducing fresh, prewarmed air into the lounge and bedrooms. Though you don’t need an MVHR until your airtightness results get an air permeability of 3.
Do you know that airtightness of your home?
Unless you’re lucky enough to live in a Passivhaus, then it’s unlikely that you do. New build homes will come with an EPC with an airtightness test result, but it’s unlikely that this result is for your home. As few as 2% of new homes are tested in larger developments (over 40 dwellings). And as most of us are living in buildings built before the 2002 legislation made testing mandatory our homes will not have been tested.
So as you can imagine, we have been very excited to work with the Build Test Solutions team on the trials of their new PULSE testing system as this meant that we were all able to find out the performance of our homes. And the results were a little surprising.
Blower door testing is currently the standard test to identify air leakage rate of any building. The blower door is simply a powerful fan that is fixed in to an exterior doorway. A pressure gauge is used to monitor pressure differences inside and outside the home as the fan introduces air or removes it to a pressure of 50 pascals to give the buildings airtightness result. The process can be time consuming and will miss any issues with the doorway the fan is set into.
The new PULSE system can test the air leakage rate without the need for a blower door fan, and measures at standard atmospheric pressure. It works by releasing compressed air into the home for a period of 1.5 seconds from an air tank. This generates air movement through air cracks or openings and in turn also creates a PULSE wave in the internal pressure.
Tests are currently being carried out on a large sample of different types of homes built to differing degrees of airtightness. So far results are looking encouraging with a positive correlation between the results for each system, suggesting they are a comparable system.
Unfortunately, at the moment there isn’t a way of using the pulse system to detect air leakage. A benefit of the blower door system is it can detect where there are leakage areas within the building. Using your hand, a smoke pencil or thermal imaging camera when the building is depressurised to locate areas where the air is able to be sucked into the building. This give the project team the option to seal uncontrolled leaking from the building. This can be really useful on retrofit projects to enable these areas to be targeted.
As part of the Pulse trial the team have each had their own homes tested, a Victorian terrace, a 1970’s and a 2014 mid-terrace new build. As you can imagine we thought the winners was assured, especially with a SAP certificate recording airtightness at 5.8m3/h/m2. The results for the new build came back 10.8m3/hm2 this means it fails building regulations and shows that the building industry still aren’t understanding the importance of making a home airtight and taking the time to achieve these low air leakage values. The results of the Victorian terrace 10.7m3/h/m2 and the 1970’s build 7.9m3/h/m2
There is more information in our airtightness read blog. If you would like to find out more about the new PULSE machine or would like to improve the airtightness please contact us.