Ice Dam Prevention: New England Homeowner's Guide

Ice dams form when heat escaping into the attic melts snow on the upper roof, the water runs down to the cold eave and refreezes. The ridge of ice that builds up forces water back under the shingles.

The durable fix is air sealing and insulation at the attic floor, followed by balanced intake and exhaust ventilation. Roof rakes and heat cables treat the symptom.

During a replacement, a self-adhered ice and water membrane should run from the eave up past the interior wall line, and through every valley.

If you already see staining on interior ceilings near exterior walls, get the attic inspected before the next thaw rather than after it.