The answer to 'roof ice dam' is that a roof ice dam is a ridge of ice that forms at the edge of a roof, preventing melting snow from draining properly. This can lead to water backing up under the roof shingles and causing leaks and damage to the roof, walls, and interior of the home.
Common causes of roof ice dams include inadequate insulation and ventilation in the attic, which allows heat to escape and melt the snow on the roof. This melted snow then refreezes at the roof's edge, creating the ice dam. Symptoms of a roof ice dam include icicles forming along the roof's edge, water stains on interior walls and ceilings, and damage to the roof shingles and gutters.