Insulation is really important when it comes to saving energy in our homes. With more insulation in our walls, roofs, and foundation, less heat escapes via conduction to the outdoors. Insulate well!
All right. That’s pretty clear.
But insulation isn’t everything. There’s also air leakage, which has a huge impact on both energy consumption and comfort. I’m used to embarrassing myself, so let me use our house as an example.
When I bought our house in 1981, it needed a lot of work. Built around 1785, it had been “modernized” in the 1970s, with drop ceilings, shag rugs, fake barnboard siding around the fireplace, brushed aluminum “tiles” around the kitchen sink and stove, tacky modern windows, and extra partitions here and there to create more guest rooms for the Long Island owners and their friends coming to Vermont for ski weekends.
The previous owners had put a lot of money into the house — though almost nothing to improve its energy performance, other than insulating between the floor joists from the basement — and that fiberglass insulation was installed with the facing on the wrong side so that most of it had long since become waterlogged and slumped to the dirt floor in a soggy mess.
I systematically — if somewhat naively — went through the house gutting it room by room, replacing rotted sills, re-siding the exterior, insulating the wall cavities, adding a continuous layer of interior rigid foam insulation, and installing new drywall. When I was done, the walls were reasonably well-insulated (though I would add far more rigid insulation were I doing the work today).
But the house remained incredibly uncomfortable. A few years later, now married and with a baby crawling around on the floor, we had to do something about the discomfort. We heated mostly with wood, and with a roaring fire in the wood stove the room temperature could be in the lower 80s at the ceiling but in the 50s at the floor.
With thick slippers, my wife and I were reasonably comfortable, but when we picked our year-old daughter up off the floor, she was cold! We felt terrible — and worried about her health. The insulation — by early 1980s standards — wasn’t too bad, but the house was anything but comfortable.
Enter the Draft Detective
I did some asking around and hired Dick Cartelli (a.k.a., The Draft Detective) from Putney, Vermont to figure out what was going on. He came in with his “blower door” and tested the home’s leakiness. A blower door is set up in an exterior door frame and turned on to pressurize the house (pictured with this blog is the Minneapolis Blower Door from industry leader The Energy Conservatory). By measuring how much air is being pushed through the blower door and measuring the pressure difference between indoors and out (using two manometers), the operator can calculate the air tightness of the house — usually in “air changes per hour” at the elevated pressure of 50 pascals.
I forget the actual numbers, but the house was leaky — really leaky! Cartelli used two cases of caulk and I don’t know how many canisters of expanding foam sealant, built an insulated attic hatch door with foam gaskets at the edges, and implemented lots of other measures over a week or two to dramatically tighten the old house. By operating the blower door to depressurize the house while he worked, he was able to feel where air leakage was occurring–and seal those holes, cracks, and gaps.
The improvement was dramatic. The delta-T (difference in temperature) from floor-to-ceiling went from over 20° to less then 10°. That delta-T was further reduced when I insulated beneath our floor from the basement and a crawl space. We no longer had to keep the wood stove cranked at full output to maintain reasonable comfort. Our daughter could crawl around on the floor and stay warm (though her earlier experience may have contributed to the fact that she now, as an adult, lives and works in the mild climate of San Francisco!).
The bottom line
Yes, we should insulate our houses well–don’t skimp on adding insulation if you open up your wall system. But we also need to pay attention to air tightness. Drafts cause discomfort and they significantly increase heating fuel use by carrying heated house air up and out, pulling in cold outside air in the process. Adding some types of insulation, such as dense-pack cellulose and spray polyurethane foam, can help to tighten a home, but other measures are often required.
If you have a drafty house, bring in a weatherization contractor to measure how leaky your house really is, and then invest in air tightening. It’s worth it!
In addition to this Energy Solutions blog, Alex contributes to the weekly blog BuildingGreen’s Product of the Week, which profiles an interesting new green building product each week. You can sign up to receive notices of these blogs by e-mail — enter your e-mail address in the upper right corner of any blog page.