Ice dams on roofs

March 6, 2013

Cross section of house with roof dam.

By Drs. Robert & Sonia Vogl
President and Vice President, Illinois Renewable Energy Association

A homeowner near Durand called concerned about the ice dams on his roof. He wanted advice about how to eliminate them. The home consists of the original building with two subsequent additions. All three sections had ice dams.

We walked around the house to observe the locations of the hanging icicles and ice dams. While icicles are attractive, they pose a safety hazard as they eventually break off and fall, potentially injuring people under them.

We examined the house interior, starting with the basement and eventually three attic areas. We noticed shallow layers of fiberglass insulation between ceiling joists and the lack of attic ventillation. Some roof sections had no access, so we had no idea of the insulation levels.

Snow on the roof can melt from the heat of the sun or house heat reaching the underside of the roof. The water usually drains off. Under certain temperature conditions when the water flows onto the cold area over the eaves, it freezes. If the snow above the ice dam continues to melt, the water is blocked. It can move up under the shingles and seep into the attic insulation and the walls of the building. Over time, water stains, deteriorated insulation, mold and wood rot can set in. “Non-uniform roof surface temperatures lead to ice dams.”

A short-term solution involves using a snow scraper to remove the first 8 feet of snow from the roof when the depth reaches 6 inches. Snow should be removed from the shingles without damaging them, and provide pathways for the melt water to drain. Snow scrapers have a curved plastic blade affixed to a lightweight aluminum pole that can be expanded to more than 20 feet. Chipping with a hammer or pick can damage the shingles. Electric wires should not be touched by the pole, as an electric shock could prove lethal. It is best not to climb up on a sloping, slippery, snow-covered roof.

Another temporary solution is to apply waterproof heat tape along the roof edge and the rain gutters to provide a pathway for the water to flow. The electrified strips only need to be turned on as needed. Some come with timers or moisture sensors and turn on and off automatically.

It is important to look into what is causing the ice dams. Heat passing up from the house and air leaks into the attic often warm the roof enough to melt the snow. Sealing air leaks and adding attic insulation may solve the problem. Ventilating the attic from the soffits to the roof ridge helps cool the attic and reduce the likelihood of snow melt.

If a roof needs to be replaced, installing a waterproof membrane shield from the edge of the roof and beyond where the walls intersect with the roof will limit water penetration.

The Durand homeowner wanted a permanent solution to his problem, so we recommended he contact a certified insulation contractor. Armed with an infrared camera, blower door and air monitoring equipment, a contractor can isolate the problems and offer solutions. The solutions should solve the ice dam problem, while reducing heating and air conditioning costs and maintaining air quality.

Drs. Robert and Sonia Vogl are founders and officers of the Illinois Renewable Energy Association (IREA) and coordinate the annual Renewable Energy and Sustainable Lifestyle Fair. E-mail sonia@essex1.com.

From the March 6-12, 2013, issue

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