As those of you who’ve been reading this blog will know, we’ve worked hard to make Canada’s Greenest Home as air tight as possible. In fact, we’re aiming to try and achieve a PassiveHaus approved 0.6 ac/h (air changes per hour at 50 Pa depressurization). So it was exciting today to have Matt Caruana come by and bring his blower door outfit and his laptop to give the house a first trial run! This is in advance of having Ross Elliot from HomeSol Building Solutions, our official energy rater, come by next week.
And it’s a good thing we had a first-round test with Matt!…
The first test showed that, despite all our efforts, there were some significant areas of leakage. Fortunately, they are all areas that can be addressed before the next test.
Our result for the first test was 3.15 ACH50, with an equivalent leakage area of 74 square inches (about an 8×9 inch hole in total over the 3,780 square feet of wall area, or 1/7355 of the wall area). What happened? Where were the leaks?
The good news is that we did a really good job of sealing the common areas of leakage. We detected barely any leakage from any of the windows, electrical boxes or seams between foundation and floor or between the two upper floors. All our efforts to make these areas tight definitely paid off.
There was some leakage from our temporarily taped up attic hatch and the cover over the temporary back door. These can be better taped next time around and that will definitely make a noticeable difference in the results.
By far the leakiest area was around the edges of our site-baled north wall. Despite using air fins at all the seams with the prefab walls and the ceiling, the upstairs north wall was leaking significantly all the way around where the plaster had shrunk away from the edges. A quick calculation of this 1/8″-1/4″ gap all the way around the whole north wall says that this could account for almost all the leakage area Matt detected.
Surprisingly, the downstairs north wall, which is built in the same manner, using the same detailing, had barely any detectable leakage. Visually, the separation of the plaster is the same thickness, and we used the same plaster mix and plasterers, and the air fins were made in the same way. Our best guess is that the mesh over the air fin may have been better embedded in the plaster downstairs, keeping the plaster tighter to the wall. The takeaway lesson for us is that while this detail can work, it’s definitely not a guaranteed way to seal this seam.
Similarly, there were leaks along the edges of a few of the prefab straw bale wall panels. They were detailed in a similar way to the site baled walls, with an air fin under mesh around the edges of the plaster. And again, some worked very well and others did not. We’ll have to do more thinking about how to make this a more effective and reliable detail on future builds.
Fortunately, these leaky areas can be easily addressed by caulking the gaps between the edge of the plaster and the abutting wall. There is still another layer of finish plaster to go on the walls as well, which will further help to seal and protect the caulking. We’ll take care of these areas before the next blower door test, and then be able to focus in on finding the smaller holes!
A result that sees the house achieve a result somewhere between the 1.5 ACH50 of the R2000 program and the 0.6 of PassiveHaus would make us really happy!
Our results today point to the difficulties involved in making buildings as air tight as possible. We had drawn careful details at the planning stage and spent a lot of time and energy on site making sure those details were well executed, and still didn’t get a great first result. Because we’re taking the time to test at multiple stages, we will find these leaks and fix them. But not every house will get this attention to detail, without which air tightness is a nice idea but unlikely to become a reality. Each and every member of the build team needs to have air tightness in mind as they do their work, and builders need to plan for the time it takes to test and address issues. It would help if such blower door tests were mandatory!