Ice Dams: Why They Form and How to Prevent Them

Big icicles and a thick ridge of ice along your roof's edge look pretty. But that ice dam can push water under your shingles, and into your walls and ceilings. Here's why it happens, and how to stop it.

1. Why It Forms

Heat from your house warms the upper roof, and melts the snow. The water runs down to the edge, which is colder, and freezes again. The ice builds up, and traps more water behind it.

2. Where The Heat Comes From

According to University of Minnesota Extension, in many homes most of that heat leaks into the attic as warm air, through small gaps in the ceiling.

3. Right Now: Rake The Snow

After a big snow, a roof rake lets you pull snow off from the ground. No snow, no meltwater. Go gently, since rakes can scratch shingles. And don't climb on an icy roof. Call a pro.

4. The Real Fix: Seal Air Leaks

The lasting fix is to seal the air leaks between your living space and the attic first. Then add insulation if you need it. A contractor can test your home to find the leaks.