Angie's LIST Guide to
Ice Dams

When snow built up on a roof begins to melt and then refreezes, an ice dam can form leading to leaks when the next thaw comes.


Winter roof leaks can be caused by ice dams in which snow on a roof melts unevenly, often due to poor insulation in the attic.
Winter roof leaks can be caused by ice dams in which snow on a roof melts unevenly, often due to poor insulation in the attic.

What are ice dams?

An ice dam is a ridge of ice that forms at the edge of a roof and prevents melting snow from draining off the roof. Spotting one quickly can help curb the damage to your home.

During periods of freezing and thawing and refreezing, water becomes trapped above the ice and finds its way beneath the shingles causing a leak inside the home. The lower the pitch of the roof, the more likely there is to be this problem.

Ice dams can lift roofing shingles and let water filtrate in. They can also pull gutters off, which can cause structural damage and lead to potential internal flooding. Hanging icicles might indicate ice dam formation.


Although ice dams can form on nearly any roof simply due to a particular freeze-thaw cycle of the weather, there can be other causes as well.

Chiefly, poor ventilation and temperature control within the attic can make one house prone to ice dams while neighboring houses are not. This happens because too much warm air in the attic contributes to the snow melt on the roof even if the outdoor temperature is not warm enough to cause it. Blocked by the ice, the water pools up and eventually finds its way beneath the shingles.

Ice buildup also happens if the gutters were poorly cleaned in the fall. A clogged downspout causes melting snow to accumulate in the gutters and refreeze. More ice forms as icicles hanging from the frozen gutters. In addition to the risk of ice dam leaks, the weight of the ice can bring down the gutter or make it sag — causing it to drain poorly even when there is no clog.

Ice shields and heated gutters

You can also have an ice shield installed along the lower edge of the roof line. This is relatively inexpensive to do when a new roof is being installed, but much more expensive to add to an existing roof.

Another trend is heating the gutters. If improving the ventilation of your roof to prevent icicle formation isn’t in your budget — or if you've already tended to that and still get ice dams — consider a heated gutter system. You may have seen — or used yourself — heated cables used on roofs to prevent ice buildup. Heated gutters follow the same principle. With a cover to help keep leaves and debris out of your gutter, it’s an all-seasons bonus for this investment. You will, however, need to hire a separate electrician to do the wiring for the heating element. But the time, energy and worry you’ll save during the winter months could be worth the investment. Large icicles can rip your gutters off, which requires an expensive fix.

Roof snow removal

If you know ice tends to form in a section of the roof, minimize the problem by raking or shoveling snow off the roof before it freezes. Sometimes this can be done from ground level by the homeowner using a special rake made for this purpose. However, it’s not a good idea to climb up on your roof in winter. Instead, hire a highly rated professional to remove heavy snow.

If an ice dam already formed, you can carefully chisel out a furrow to allow the water to escape, but this is risky. Make sure you stop before you reach the shingles or you may cause more damage.

For those who want to go the DIY route, roof salt products that thaw ice are available. However, don't use salt or calcium chloride as both are corrosive and any runoff will damage grass and plants.

Dos and Don'ts

1. Call a professional. Removing an ice dam can be quite dangerous. A good place to start is with a reputable roofing contractor. Check Angie’s List and get estimates and references from contractors in your area. Gutter cleaning companies may also offer this service.

2. Remove snow from the roof. If you’re tackling the job yourself, there is a special tool for removing snow called a “roof rake.” Carefully pull it down the slope of the roofline. Never pull snow across the roof. You could damage the shingles.

3. Chip away at the ice. For immediate action, you can chip away through the ice dam so the water can flow through. Stop when you get close to the roofing.

4. Properly ventilate and insulate the attic. The main cause of ice dams is an overly warm attic.

5. Never walk on a snow-covered roof. Make sure you work from a ladder to access/fix the damage.

6. Do not install mechanical equipment or water heaters in attics. These are a fire hazard. Stick to insulation to help keep heat in your home.

7. Do not use salt or calcium chloride to melt snow off the roof. These chemicals are very corrosive. The runoff of these chemicals can also damage grass and plants.




Almost more important then insulating is air sealing the attic. Warm air rises and will pass through insulation- only to condensate in the cold attic. Bypasses- unintentional openings between heated and non heated spaces speed the warm moist air movement greatly increasing ice dams.

its hard to get enough insulation at the outside walls of a house due to most have trusses and that only allows for 3.5 inches of rafter height above the wall in that area and if it has 2 x 6 rafters that only allows for 5.5 inches of rafter height at the outside wall, so i think if your building a new home, it should have a 12 inch wall built above the wall so that you can get 12 inches of insulation at the outside walls of the house and have an r 32 : i think it is : rating there preventing the warmth of the house to melt the ice and refreeze it causes a dam there,,

This article was very helpful--thank you!

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