Installing roof/gutter de-ice cable

[Dana Smith]

Hello, I am an electrician by trade. I have installed plenty of heat cable in masonary type floors. I live in Colorado in an area where 16'' snows are not uncommon.
My neighbor who has an asphalt shingled roof is having problems with ice damns. He is considering installing Heat cable on the eves and in the gutters. He asked me what I thought. I have never installed this stuff on a roof. That which I have seen melts the snow around the cable itself but does nothing for the rest of the roof. With asphalt shingels the snow on the roof will not slide. What I would like to know is will heat cable prevent the ice damn problem or will the ice damn develop above the area where the heat cable is installed on the eve or lower 2 feet of the roof.? In fact my neighbor did "roofrake" the lower 2 feet of the roof and actually had problems with ice damns above that area. I told him to consider a metal roof. He was not ammused, as it is a fairly new house.

Any info you could send my way would be appreciated.

Thanks, Dana.

[Rich]

Personally I think that the ice dam will form above the heat cable and it'll just increase the problem. Typically when you see ice damming there is something causing it on the interior of the building. Most often it's proper air flow - trying to keep the cold side cold and the warm side warm. Ice and water shield will protect a little longer from ice getting behind shingles.. but not much more than that.

[grumpydasmurf]

My opinion of the heat cables is they reduce the effects of the ice damn but won't prevent ice damns from forming. The only way to cure ice damns is with insulation and ventilation.

Ice shield doesn't prevent ice damns either, but like rich said it's a protection. It's much much more difficult for the ice to get through the ice shield. Ice shield is typically installed in 3' sections in my area. This means if you have a 4' ice damn, you have 1' of unprotected area. Oops.

Look in the attic for insulation obstructing the intake ventilation. This is very common with blown insulation. go to www.rollvent.com and see if the attic ventilation is adequate. More ventilation may need to be installed.

Also condensation problems are sometimes mis-diagnosed as ice damning. Look inside the attic on a freezing day. If you see ice crystals all over the framing, congratulations you have condensation :)