How Do You Prevent Ice Dams From Forming on a Roof?

Ice dams form when heat escaping from your house warms the attic and melts snow on the upper part of your roof. The resulting water runs down the roof slope until it reaches the much colder overhang, or eave, where it refreezes. This cycle gradually builds a ridge of ice along the roof edge. That ice dam then traps more melting water behind it, which can force its way under shingles and into your home, causing significant water damage to ceilings, walls, and insulation.

Warm air leaking from your house into the attic is a major contributor to ice dams, often undermining even good insulation. You need to find and seal these bypasses to stop the flow of heated air. Common sources include gaps around plumbing vent pipes, recessed light fixtures, attic hatches, wiring holes, and the top plates of walls. Use caulk for small cracks and gaps, and expanding spray foam designed for this purpose for larger openings. A thorough sealing job makes your insulation much more effective at keeping the roof cold.

Regular roof and gutter maintenance supports your primary prevention efforts. Keep gutters and downspouts clean in the fall so melting water can drain away instead of pooling and freezing at the edge. When replacing your roof, consider installing a waterproof membrane, or ice and water shield, under the shingles along the eaves. For existing roofs, you can use a long-handled roof rake after a snowfall to carefully remove snow from the lower three to four feet of the roof edge, reducing the source material for ice dams.