Mind the Gap: Take Two

December 10, 2019:  Finally, it was time to find out how well I’d done. In the last few days, the electrician had made a lot of holes. Had I followed up with each one? Did they all get hit with caulk or tape?


Subway Station, somewhere in Great Britain

Jim Kjorlie of Kjorlie Design Services arrived with his blower door kit. This was going to be my second of three tests—and the most important. The drywallers were due in a week, and this was my last chance to make things right. I really, really wanted a good number. My goal was a “1”.

An airtight building shell is essential for the kind of house I’m building, and a blower door test is the only way to know for sure you have it. Jim has tested hundreds of homes in the Madison area. The best result he’s seen is 1.2 ACH (air changes per hour)—literally how many times the volume of air in the home is changed out with fresh air from leaks in the building shell.

Wisconsin’s Uniform Dwelling Code allows a new home to be as leaky as 7.0 ACH, though studies have shown that the average new home here tests out at 4.0 ACH. Some neighboring states mandate 3.0 ACH. Some really meticulous builders are hitting 0.5 ACH or less. Is all that caulking and taping worth the extra cost? I’d argue that a well-sealed home insures against more than high utility bills: it insures against moisture, mold, mildew, and insect problems. Even so, out of curiosity I ran the numbers on my house through a modeling program called REM Design:

Poem Home @4.0 ACH = $908/year heating costs @0.12/kWh
Poem Home @0.6 ACH = $630/year heating costs @0.12/kWh

Jim set up his equipment by propping open the front door and replacing it with a fan attached to an adjustable shroud. The fan slowly depressurizes the house to simulate a 20 mph wind bearing down on all sides. Drafts that normally aren’t felt are suddenly amplified. My friends Eric and Lew stopped by to see how it’s done, and thanks to their sleuthing, we found two major leaks.20191210_133505

Cold air from the mini-split was pouring out the narrow gap between the unit and the drywall. We later found out that the installer hadn’t sealed or insulated the line set connecting the outdoor unit to the indoor unit.  I can stuff this with fiberglass.

The second leak was at the fixed panel of the patio door. A steady draft was easily detected by waving a hand over the crack between the frame and the sash.  I can caulk this.

So how did I do? We got a 0.87. Yeah! “Don’t celebrate yet, Amber” is what Jim didn’t say but implied. He’ll be back for a final test when the house is complete.

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