Q&A / 

Ice Dam Video

Hi, I'm Tim Carter from AsktheBuilder.com and I'm outside, as you can probably see some snow falling. A really big snow storm is headed this way. I want to show you someone that a lot of people don't get to see up close and personal. It is an ice dam on the roof.

What has happened is this. If you look under the roof ice dam, you will see the soffit and the exterior of the house. Well, guess what's happening? Right behind the ice dam where you can see the shingles. There is enough heat that can pass through the insulation and radiates to the underside of the roof deck. This heat melts the snow pack.

As soon as the melted snow flows down the roof and touches the ice-cold gutter, it starts to freeze instantly. As this process continues, the ice damming gets thicker and thicker.

On another area of the roof, there are no ice dams. So why is there no ice here? What is different? This roof is over the garage and there is no heat in the garage. Thus, no heat comes up and heats the underside of the roof. Melting the snow pack and causing it to freeze when it hits the cold edge of the roof.

If you want to prevent ice dams, there are a couple of choices. First thing is to get the snow off the roof. Don't beat the roof chopping ice, remove the snow pack with a snow rake.

Another one of the ice dam solutions is putting a radiant barrier on top of the insulation, making sure it doesn't touch the insulation. This barrier would run up the underside of the roof leaving an air gap of about 1-1/2 inches on top of the radiant barrier. This barrier would cause all that escaping heat to be deflected back down into the house.

If you want to stop the ice dam leaks, you will need to put an ice and water shield on the roof. (Click here to watch my Ice and Water Shield video.) This ice dam membrane will prevent the water backing up behind the ice dam from getting into the house as the water gets under the shingles. In heavy snow areas, like New England, the ice and water shield needs to extend up the roof about six feet. Better yet, apply it to the entire roof. This ice dam membrane can only be put on when you are re-roofing or building a new home.

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6 Responses to Ice Dam Video

  1. Tim, I watched this video last winter as I was having a similar problem in my 1948 house, here in Edmonton. I was getting an ice dam in one specific spot, which was exactly in line with an interior wall that was perpendicular to the exterior wall.

    I followed your advice and stapled a radiant heat shield to the rafters surrounding the area beneath the hot spot on the roof. I used the aluminum "bubble" sheeting". I also added fiberglass insulation in line with the top of the interior wall.

    This winter the problem was drastically reduced compared to the previous winter. There is still a bit of a warm spot on the roof (though much less), but I believe that is due to a secondary problem -- the interior wall is leaking warm air up into the attic.

    This interior wall is thicker than normal, as it contains the plumbing vent stack, and there's also a heating duct(!) inside it. I've decided the solution will be to open up the drywall when I get around to repainting the room, mostly in the top corner where it meets the exterior wall, and shooting expanding foam in to seal it up and insulate it.

    To sum up, your radiant heat shield solved my problem 90%, and was a very easy fix. the rest I'll take care of soon.

    Thanks for the great advice!

  2. I am curious as to why you did not mention a solution to the ice dam issue. What about eliminating the warm air that is escaping from the home with air sealing? And after air sealing, improving the existing insulation. That will reduce or eliminate the cause in the first place.

  3. What do you think of the new ice dam salt blocks advertised on TV? Will they ruin or degrade the shingles? Do they really work? Recently had a tumor removed in my head and balance is an issue so climbing on the roof is dangerous. I do use a roof rake, but ice dams still form.

  4. I don't know what a radient barrier is?

    Can this material be stapled to the bottom of the rafters holding up the roofing band shingles?

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