We've been working hard lately to get ready for having at least on half of the SuperGreen duplex ready for hanging the drywall. This means getting all the electrical, plumbing, ventilation and the last of the insulation all in place. But most importantly, it means completing the pre-drywall Air Leakage Test. Craig, our Energy Adviser and Green Rater, was kind enough to come late in the day Friday to do the test on #40 Nijmegan. We'd been busy for most of the day preparing the for test finding all the holes and sealing them up.
I forgot to take a picture during the blower door test, but they are pretty standard now days, so I'm sure most folks know what one is - otherwise, just look up
Blower Door on Wiki.
Fixing Holes
The approved method for sealing holes in a poly vapour barrier is with a poly patch, acoustical sealant and then mechanically closing (clamping) the patch. Most builders simply use the red Tuck Tape. That seems to work well enough, but technically, the red tape is not approved for sealing the vapour barrier. Because we're building this house for a long life span, we chose a "belts-and-braces" approach - the approved method of acoustical sealant and mechanical clamping AND red tape!
We also went and mechanically closed all joints in vapour barrier. Again, this is the recommended best practice, but you don't often see this being done. The issue here is that over time, as you open and close doors, it pressurizes and depressurizes the house, causing the joints in the vapour barrier to open up (think of inflating and deflating the house). To prevent the joints from opening up, you should mechanically fasten the joints closed. In our case, strips of 3/8" plywood attached to the studs did the trick.
Blower Door Test
As soon as the blower door turned on, the house very quickly depressurized. Now, that sounds like a bad thing, but it means that it is a very air tight house. In a high performance, energy efficient building, you want there to be almost no uncontrolled air leakage. Uncontrolled air leakage is a bad thing, it means either:
- cold air leaking in (energy loss); or
- moist indoor air leaking out (possibly damaging the building).
Of course, you need fresh air in the building, and that is why a ventilation system is so critical to a healthy building. A heat recovery ventilator (HRV) is a must and we are installing just about the highest performance HRV available in the North American marketplace. In fact, because there the home will be so energy efficient, the house only requires a minimal heating system (a couple of small baseboard heaters) and so the ventilation system will be the most advanced piece of machinery in the building. Insulate well and Keep it Simple!
Results
The pre-drywall air leakage test showed the house is extremely air tight. A common measure of "leakiness" is Air Changes per Hour (or ACH) at -50pa. The City of Whitehorse's new energy efficiency building bylaw allows a maximum leakiness of 1.5 ACH. We achieved a 0.75 ACH. My own personal house which is a GreenHome with EnerGuide Rating of 81 has 1.1 ACH.
0.75 ACH may seem a bit high for such a high performance building, but this measure is a bit misleading for a small building. Air Changes per Hour are a function of building volume. So, a small hole creates a comparatively large "leak" in a small house. The same hole in a large house with a large volume would create a much lower ACH rating.
Another way to look at the air leakage is the equivalent leakage area. In our case, it was only 9 sq. inches. That means if you put all the holes in this building together, it would be a 3" by 3" square! Most well built houses have on the order of 40 sq. in. of leakage area. So we are 1/4 the leakage of a well built modern house. Craig says this maybe the tightest house he's ever tested.
The house will be testing again at completion, and we anticipated the leakage will increase a bit once all the ducts are in place (range hood, dryer, etc.) that may add a bit of leakage.
Lastly, with this new, low air leakage rate, our projected
EnerGuide Rating for #40 Nijmegan Rd is
86: it's well on its way to becoming the most energy efficient house in Whitehorse.
Now we are ready to labour away over Labour Day finishing the insulation so the drywall can go on next week.
Congratulations to the whole team for working hard to make this deadline and still do a quality job on this high performance home!
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