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Just wondering if anybody know much about the heat tape or wire you can run on the last couple feet of your overhangs to stop ice from building up and creeping under the shingles. Does it work very well? Are there any drawbacks? Thanks.
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I've used those things. Seemed to work pretty well. I had an 'L' shaped ranch with a low slope roof and used to get ice dams all the time at the valley. I would only plug it in long enought to melt holes through the ice, then I would unplug it - something about heating up the outdoors troubled me.
Of course, the real solution is to insulate the attic and ventilate the roof, which is what I eventually did. Then I sold the house.
*Here is how I would look at it. Ice dams are caused by heat loss through the ceiling and building envelope (ie. heat that cost you significant money to generate). The cause of the heat loss may be inadequate insulation but probably more likely air leaks through the building envelope. The concept of trying to solve the end result of the problem (ie. ice dams) by using heat tape (ie. throwing away more wasted money on higher electric bills) seems foolish.It would make more sense to try to solve the underlying problem. This is much more complicated but not necessarily much more expensive. It may require some air sealing work in the ceiling plane, some additional attic insulation, etc. etc.. In the long run though you will be much better off.The ice dams are only the symptom of the problem.
*As Jim argues, fixing the underlying probelm is a better solution. Ideally, build a "cold roof" instead of a hot one. If using a "hot roof", install Water & Ice or another membrane designed to more thoroughly waterproof the eaves. But that can be a lot of $$ to retrofit.If you resort to the heat-trace cable, DO NOT cross it. Crossing the cable creates a hot spot where they touch and greatly increases the chance of a fire. That stuff does sometimes catch fire, even in the winter so do a careful installation, inspect each fall, and reinspect if the snow has slid on the roof.To answer your question - yes, the cables work to mostly eliminate ice dams on roofs. Or rather, to provide drainage through the ice dams. Note that there are only certain conditions that create standing water behind the ice dam and those are the only times you need to turn the cable on. To have standing water behind an ice dam, there must be subfreezing temperatures (above freezing, the ice dam itself melts); there must be a blanket of insulating snow on the roof; lastly, the temperature of the shingles must be above freezing. This last condition is hardest to assess (but a remote reading thermometer would help). The ratio of 38F (70F inside minus 32F at shingles) to how subfreezing it is (10F is 22 below freezing) must exceed the ratio of roof (fiberglass) insulation to snow insulation. So things are better with colder outside temps, more insulation, and less snow. When it is really cold, the shingles are below freezing and ice dams are not a problem (until it warms up). If you've shoveled your roof, you can't get an ice dam. More roof insulation and better air tightness will reduce the melting rate and the conditions under which ice dams form. A "cold roof" will not form ice dams. Good Luck, David
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Just wondering if anybody know much about the heat tape or wire you can run on the last couple feet of your overhangs to stop ice from building up and creeping under the shingles. Does it work very well? Are there any drawbacks? Thanks.