Ice Dam

An ice dam is a ridge of ice that forms at the roof's edge when melting snow refreezes, blocking drainage. Clogged gutters make ice dams worse by trapping standing water that freezes solid.

Ice dams form when attic heat melts snow higher on the roof, the water runs to the cold eaves, and it refreezes — building a dam that backs water up under the shingles and into the home. Clogged or poorly draining gutters dramatically worsen the problem by holding standing water at the very edge where it freezes first. The root fixes are attic insulation and ventilation, but keeping gutters and downspouts clear (or guarded) so water keeps moving is a key part of prevention, especially in freeze-thaw climates.