Mind the Gap: Take One

May 15:  There’s a lot of confusion out there about how tight is too tight. Some builders say a house “needs to breath”, and that sealing every gap is a waste of time. This is how I see it: we all want fresh air. Some of us with allergies need filtered fresh air. What we don’t want is “fresh air” filtered through the building materials in our walls and ceilings. If we leave gaps we are:

1. Wasting energy (losing heat in winter, coolness in summer).
2. Allowing moisture-laden air a route into walls and ceilings, where it can condense on cold surfaces, creating a breeding ground for mold and mildew.
3. Allowing dirty or polluted air a chance to dump dust and allergens into walls and ceilings, or directly into the indoor air.
4. Creating a pathway for insects, or worse—rodents.

In the summer, I can open windows. But in the winter, I’ll need a mechanical system to bring in fresh air and exhaust stale air. Later, I’ll explain the quiet, energy-efficient ducted heat-recovery ventilator (HRV) that will be installed.

Just as I did for exterior air-sealing, I took an enthusiastic approach to interior air-sealing. I used canned spray foam to seal window and door rough openings. It was easy and fast. I’m a little worried about reports I’ve read that foam can crack and separate from it’s wood substrate over time. A bead of caulk or a run of tape over the foam would be prudent, but I haven’t found a way to do that in my particular situation. Where spray foam wasn’t appropriate, I used caulk or tape.

foam     flex wrap     Foam in all its guises is one of the worst building materials for carbon footprint. I chose a low-pressure polyurethane foam called Handi-Foam. It’s a Green Guard Gold product certified for low chemical emissions and is non-toxic when cured.

The electrician has run a few pipes. I sealed those with DuPont’s FlexWrap EZ, a butyl-based peel & stick tape that’s a breeze to install.

With air-sealing complete, the moment of truth arrived—my first Blower Door Test. I’ve arranged for energy auditor Jim Kjorlie of Kjorlie Design Services to come out and test my house three times: before insulation, after insulation and before drywall, and finally upon completion. With his help, I hope to be certified through Focus on Energy’s New Home Program.

blower door

Blower Door tests aren’t too common around here, but in neighboring states where stricter energy codes have been adopted, they’re required. Jim set up a large fan in the front door, turned it on, and brought it up to speed. The idea is to depressurize the air to simulate a 20 mph wind bearing down on all sides of the house. Drafts can then be hunted down. Gauges and gizmos spit out numbers—and you either “pass” or “fail”. Here’s how I did, expressed in air changes per hour (ACH)—literally how many times the volume of air in the home is changed out with fresh air each hour:

Wisconsin Code (2009 IECC national code)      =7.0 ACH
Focus on Energy New Home Program              =3.8 ACH
Test #1                                                                     =2.6 ACH

smoke

It’s good, but I was hoping for better, like 1.0. Jim went around with a “smoke stick” that detects leaks by showing a trail. Tell-tale puffs shot out at the base and top of the patio door—the usual places, he said. He suspects that the fiberboard vent chute—which comprises 40% of the interior surface area is much more air permeable than the plywood sheathing on the walls. He suggested I find air-perm ratings for both materials, but so far I haven’t found any definitive information.

I’m stoked to bring that number down, so stay tuned for Test #2!

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