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Ice Dams Cause Winter Woes

Although the glistening icicles hanging from the edge of your home may remind you of a winter wonderland, they might actually be a symptom of a larger problem – ice dams.

What is an ice dam?

An ice dam is a ridge of ice that forms at the edge of a roof and prevents melting snow from draining off the roof. Because the water has no place to go, it backs up behind this ridge of ice and can leak into the home. These leaks can damage walls, ceilings, insulation and other areas.

What causes an ice dam?

Two things are needed for an ice dam to form: snow on the roof and a warm attic. Inside the house, warm air leaks into the unheated attic. Warm areas are created on the roof, causing snow on the exterior roof to melt. Melting snow moves down the roof slope until it reaches the cold roof edge, where it refreezes. As this process continues, ice builds up along the eaves and forms a dam. As more snow melts, it pools up behind the dam and causes water to seep between the shingles. This water finds cracks and openings in the exterior roof and enters the attic space. From the attic this water could affect walls, ceilings and insulation inside the house.

Ice dams can also cause structural framing to decay and metal fasteners to corrode. The moisture can also lead to the growth of mold and mildew in the attic and on wall surfaces.

Why is the attic warm enough to melt snow?

Heat escapes into the attic in two major ways. Conduction occurs when heat flows from warm materials to colder materials. Convection occurs when warm, moist air rises and leaks out of the living space, carrying heat with it. Typical attic insulation slows conduction but does not plug air leaks or prevent convection.

How to correct and prevent ice dams.

An immediate solution requires removal of the snow from the roof. A roof rake or broom will easily remove the snow but may damage roofing materials. Instead, try using a sidewalk snow melt product. Note: Performing work on a roof during winter is risking personal injury. Please contact a professional to do the job.

To prevent further ice dams, first measure the attic insulation. If there is less than 12 inches of insulation, valuable heat is being wasted (remember that once you have reached R-44, adding more insulation does not provide any added benefit). Second, study the way snow is melting off the roof. Snow melting evenly from the entire roof usually indicates inadequate insulation or may indicate substantial air leaks into the attic. Snow melting more rapidly in some spots than others almost always indicates smaller, localized air leaks. These “hot spots” are especially likely to do substantial damage to the roof and house framing.

Electrically heated tape or cables are poor quick-fix solutions. They are expensive to install and require a considerable amount of electricity to prevent ice formation. Heating must be done before ice dams form, not afterwards. They can also cause shingles to become brittle over time, creating a fire hazard.

Most ice dams are caused by warm air leaking into the attic from the house. While an expensive roof repair job will correct the damage, it will not correct the cause of the damage.