NEWS for North Dakotans
Agriculture Communication, North Dakota State
University
7 Morrill Hall, Fargo, ND 58105-5665
February 12, 1998
Ice dams along the edges of house roofs may be a bigger problem for homeowners this year because of the mild winter, according to a North Dakota State University engineer.
Ice dams are most likely to occur at temperatures just below freezing. Icicles hanging from the eave and ice formations on the wall near the soffit are likely indicators of ice dam formation, Ken Hellevang says.
"Heat from the house warms the roof and melts the snow," explains Hellevang. The water freezes when it reaches the colder eaves, forming a ridge, or dam, of ice at the edge of the roof. Water behind the ice dam may find its way between and under shingles where it can damage the building materials. Shingles, eave gutters and flashing can also be torn from the roof by the weight of the ice. In addition to damaging the structure, the moisture may create a health hazard because wet areas are conducive to mold growth.
Snow should be removed from the lower portion of roofs of houses that are experiencing ice dams, he says. Ice dams will continue to form if there is snow on the roof, the roof surface is above freezing and the eave temperature is below freezing.
Take care to avoid damaging roofing materials when removing snow. A roof snowrake is a good way to remove the snow while standing on the ground. Ladders, ice and snow can be a dangerous combination, Hellevang notes. Overhead power lines also pose a threat.
He also urges homeowners to use care when trying to remove ice dams. It may be best to just open channels to allow the water to escape rather than try to remove all the ice. Chopping at the dams can easily result in roof damage. Using salt to melt the ice may rust nails, gutters and downspouts, and damage the lawn. Heating cables melt the ice dam at cable locations permitting water to escape, but will not totally solve the problem, he says.
"The chief causes of ice dams are poorly insulated attic floors, air leakage from the living space into the attic and inadequate attic ventilation," Hellevang says. "The most effective way of dealing with ice dams is to address those problems."
To prevent ice dams, install more insulation in the attic floor and seal openings around recessed lights, plumbing penetrations and other openings to keep heated air in the lower areas of the house. Increase ventilation in the attic to keep roofs and eaves at the same temperature. It is best to provide ventilation through the eaves and out through the roof peak. Make sure insulation does not block airflow into the attic. Insulation baffles may be used to provide a channel for air between the soffit and the attic. Where the roof cannot be ventilated through the eaves, another option is to place a second roof deck on spacers which allows air to flow from the eave to the ridge.
An additional option is to install a continuous waterproof membrane at the eaves. The membrane should extend up the roof at least 24 inches past the exterior walls of the building.
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Source: Ken Hellevang (701) 231-7243
Editor: Tom Jirik (701) 231-9629
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Click here for a pdf version of this graphic.