Short answer
Ice dams form when heat from the house melts snow on the upper roof and the water refreezes at the cold eaves. Right now, rake snow off the lower roof from the ground and catch any drips; have the dam removed with steam. To stop them for good, air-seal and insulate the attic so the roof deck stays cold.
Why they form
Warm air leaking into the attic heats the roof deck above freezing while the overhangs stay cold. Snow melts, runs down, and refreezes at the edge, building a ridge of ice that backs water up under the shingles. Complex roofs, finished half-story rooms and recessed lights make it worse.
What to do now
- Use a roof rake from the ground to pull snow off the lower few feet of roof.
- Catch interior drips and move belongings; switch off power to wet fixtures.
- Have a roofer remove the dam with low-pressure steam.
- Don't chip with hammers or axes, and don't use salt that can damage shingles, metal and plants.
Fixing the cause
The lasting fix keeps heat out of the attic: seal gaps around light fixtures, plumbing and chimney chases and the attic hatch, add insulation, and make sure soffit intake and ridge exhaust are clear. When you re-roof, model codes in cold-climate areas require an ice barrier from the eave edge to at least 24 inches inside the exterior wall.
Where ice dams are common
New England, New York, Pennsylvania, the Great Lakes states, the Upper Midwest and mountain areas of the West see the most ice dams, especially in winters with repeated snow and thaw cycles.
When to call a roofer
- Water is coming in during a thaw.
- Thick ice is building along the eaves or gutters are pulling away.
- Ice dams return every winter.
What the roofer does: see ice dam removal & prevention.
Common questions
Do heated cables stop ice dams?
They can keep a drainage path open in trouble spots, but they don't fix the heat loss that causes ice dams.
Does insurance cover ice dam leaks?
Interior water damage from ice dams is often covered by standard homeowners policies; removing the ice and preventing it usually isn't.
Editorial note: this guide is general information for homeowners, not a diagnosis or insurance advice. Conditions vary by roof, so a roofer should inspect and confirm the cause before any repair.