Drive-by Energy Audits
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If heat loss through your roof is going to melt snow and cause ice dams, use a snow rake to clear the snow. Here's my wife raking our roof after last week's snowstorm. Photo: Alex Wilson. Click on image to enlarge With all the snow we received in ... Usually, when excessive heat loss through the roof melts snow, you see ice dams at the roof edge. As the snow melts, it runs down the surface of the roof (under the insulating layer of snow) and freezes once it gets to the overhanging eaves--which are colder because they aren't receiving escaping heat from the house. That freezing snowmelt can form massive ice dams and thick stalactites of ice extending down toward the ground. Another very common problem--even in situations where there's lots of insulation--is air leakage at the eaves. The juncture where the top of the wall framing connects with the roof framing and attic floor joists is notoriously difficult to air-seal, so leakage is common. Warm air flows up from the house below and melts the snow at the edge of the roof. The superficial "fix" for these problems is to use a long-handled snow rake (a common Vermont tool) to pull that snow off the roof--at least the bottom four to six feet. It's best to do this shortly after the snowfall, before much melting from below happens and ice dams build up. (The photo is of my own house, with yours truly manning the camera from a safe distance while my wife carries out this important task.) With some of the snow left on the roof, you might still get ice dams (depending on conditions), but there's a greater chance that the snowmelt will run down the lower section of roof and evaporate without building up an ice dam. The real fixes to these problems are much better done in good weather: dramatically boosting the insulation in your unheated attic or roof and carrying out air-sealing. This blog isn't at all meant to suggest that we should skip a "real" energy audit as we think about how to improve the energy performance of our houses. A thorough energy audit by a weatherization contractor will include a blower-door test and, often, thermographic analysis (in which a special infrared camera is used to identify areas of excessive heat loss). But the drive-by energy audit after a snowstorm is a great way to get a quick sense of the need for a real energy audit. 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. Alex is founder of BuildingGreen, Inc. and executive editor of Environmental Building News . To keep up with his latest articles and musings, you can sign up for his Twitter feed .