Ice Dams

picture of ice dam
Photo courtesy of

What are ice dams?

An ice dam is a ridge of ice that forms at the edge of the roof (referred to as eaves) and prevents water (melting snow) from properly draining.

How are ice dams formed?

Heat from the inside of a home warms the roof decking during the winter, and combined with heat from the sun, this can melt snow on the roof.  Melting snow on the upper roof then runs down toward the eaves as water. Unfortunately, when it reaches the cold eaves and gutters it refreezes. The continual thaw and re-freeze process creates ice dams. The result: water backup under the roof shingles where it can soak through the roof decking or wall sheathing, causing damage to attics, ceilings and walls.

Ice Dam Defense

     There are three ways to defend against the damage ice dams cause: insulation, ventilation and water-proofing shingle underlayment. All three work together. Insulation keeps heat from escaping from your home’s living space into your attic. Ventilation removes the heat and helps keep the roof deck evenly cool to help prevent snow from melting on the roof. Underlayment that protects from water damage and leakage, such as CertainTeed WinterGuard,™ is laid across the roof before roof shingles are applied.
We’ve included some pictures from one of CertainTeed’s brochures to help explain ice dams.
picture of CertainTeed Insulation brochure
picture of CertainTeed Ventilation brochure
picture of CertainTeed Underlayment brochure