Ice dams along the roof edge

What an ice dam is

An ice dam is a ridge of ice that forms at the edge of a roof. Snow higher on the roof melts, the water runs down, and it refreezes at the colder edge. The ridge grows and traps more water behind it, which can back up under shingles and leak into the home.

Warning signs

• Thick ice along the roof edge or in gutters.
• Large icicles, especially with water dripping behind them.
• Water stains on ceilings or walls near outside walls.

What causes them

The main cause is heat escaping into the attic, which warms the roof and melts snow from below. Clogged gutters make it worse because meltwater has nowhere to go.

How to help prevent them

1. Clean gutters in late fall so meltwater can drain. See gutter cleaning.
2. Ask an insulation or roofing pro about attic insulation and ventilation. That’s the long-term fix.
3. Rake snow off the lowest few feet of the roof from the ground after heavy storms.
4. Treat walkways under the roof edge, where dripping water refreezes. Ice control covers those icy spots.

If you already have one

Don’t chip at the ice with tools, which can damage shingles and gutters. If water is getting inside, call a roofer.