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Insulation and ice dams

We are getting ice dams on the south and west sides of our home. We have plenty of insulation in the attic but on those two sides (south and west) there is a covered porch. There is no insulation on the soffit that covers the porch and of course no insulation in the eaves.

The porch is about 6 feet wide and runs the entire length of the south side of the home (the front) and the entire length of the west side. The east and north sides only have eaves which are less than 12 inches.

Is there anything we can do to prevent the ice dams? Would adding insulation onto the soffit of the porch be advisable? I would prefer not to use heat tape but is this our only option?

Asked by Jared Bennett
Posted Mon, 12/09/2013 - 18:59
Edited Tue, 12/10/2013 - 09:05

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2 Answers

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Jared,
I understand that your eaves are cold, so that is where the water freezes. But the solution to your problem is not to heat up your eaves (as you probably realize). The solution is to make sure that the upper parts of your roof aren't so hot that your roofing is melting the snow and making water.

Ice dams occur because your attic is leaking heat. This commonly happens (a) if you have heating equipment in your attic -- for example, ductwork, a furnace, or a hot chimney; (b) if you have air leaks in your ceiling that allow warm interior air to escape and enter your attic; or (c) if your insulation is too thin.

To fix the problem, you have to address the problems in that order. For more information, see Prevent Ice Dams With Air Sealing and Insulation.

Answered by Martin Holladay, GBA Advisor
Posted Tue, 12/10/2013 - 09:04

2.
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I often hear about ice dams on homes only in certain locations - often south / west facing areas. Or where there is an odd shade/sun issue. Isn't sun heating up shingles in spots a risk creating water that will run down roof some distance before freezing when hitting cold snowy roof? Especially on 15-30° days... I know my driveway melts and gets wet on sunny very cold days.

Of course anyone who says "i have ice dams" followed by "plenty of insulation" always makes me wonder ...(my bro said it...and found he only had 9" and many bypasses in his old MN home).

I suppose the warmer facing surfaces of his roof will see melt/freeze more - and are the 'final straw' of sorts... where as his insulation/leaks don't quite cause the issue elsewhere. Or the bypasses/insulation in those areas are a touch worse than else where.

Answered by Nick T - 6A (MN)
Posted Tue, 12/10/2013 - 14:10

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