Ice Dam

Definition

An ice dam is a ridge of ice that forms at the eave of a roof, blocking melting snow from draining off. Water then backs up under the shingles and into the attic or ceiling, causing leaks and structural damage. Ice dams form when heat escapes from the attic, melts snow on the upper roof, and the water refreezes when it hits the cold eave. Prevention involves proper attic insulation, adequate ventilation (soffit + ridge vents), and ice and water shield at the eaves.