Glossary · Insulation & windows
Ice dam
Also called: ice dams · ice damming · ice build-up at the eaves
A ridge of ice at the roof edge that traps melting snow behind it, which can back up under shingles and leak into the house.
What it means
Heat escaping into the attic warms the roof and melts the snow above; the water runs down to the cold overhang and refreezes. As the ice builds, water pools behind it and can work under the shingles. Ice dams usually form when there's a lot of snow on the roof.
Why it matters in an audit
Ice dams are usually a symptom of attic air leaks and thin insulation, so the lasting fix is to seal attic bypasses and insulate, not just remove the ice.