What are Ice Dams and How Can They be Prevented?

I am concerned about taking care of my roof this winter to prevent leaks. I’ve heard ice dams are a concern. What are ice dams and how can they be prevented?

- Louis in Prescott

Louis, ice dams are formed when heat from the inside of a home escapes into the attic and warms the roof decking during the winter. This heat, combined with heat from the sun, can melt snow on the roof. Melting snow on the upper roof and in the valleys then runs down toward the eaves as water. When the melting snow reaches the cold eaves and gutters, the water then refreezes. The continual thaw and re-freeze process creates ice dams. The result is water backing up under the roof shingles or behind fascia boards where it can soak through the roof decking or wall sheathing, causing damage to attics, ceilings and walls. There are three ways to defend against the damage ice dams may cause: (1) Insulation (2) Ventilation and (3) Ice and water shield 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 and Ice and Water Shield Shingle Underlayment is installed at the eaves and overhangs before shingles are applied. This special underlayment helps to prevent the formation of ice dams.