How to Prevent Ice Dams
cuksoker
| Posted in General Questions on
looking for an ice damming preventive for existing shingle roof with a 4/12 pitch abutted by a mansard roof which also ice dams. live in zone 5 are the wires at gutter level still the best solution?
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No. This has been addressed many times, because it's a common problem, but Martin summarized most of the pertinent ideas in Ice Dam Basics article.
https://www.greenbuildingadvisor.com/article/ice-dam-basics
I'd start reading there. Air-sealing is likely going to be the first step in a solution. Fortunately, that's relatively cheap, and it should be done as one of the first steps in upgrading any house, so it's definitely worth pursuing. But read first. And careful with that axe while you're up on the ladder in the wintry conditions ;)
Warm air from inside the house is finding it's way to the roof deck and melting the snow. The heat flow must be stopped with air sealing and likely more insulation. It is usually the transition area right above the outside wall plate and double plate and the cold roof overhang where the ice dams occur. Insulation is thin at this point so the flow of heat to the roof is often considerable. Modern, well designed structures will use rafters with a deep energy heel to allow for adequate insulation and venting beneath the roof deck.