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Ice Dams and Attic Condensation

Ice Dams

Ice dams sometimes occur on sloping roofs in climates with freezing temperatures. When the temperature in your attic is above freezing, it causes snow on the roof to melt and run down the sloping roof. When the snowmelt runs down the roof and hits the colder eaves, it refreezes.

If this cycle repeats over several days, the freezing snowmelt builds up and forms a dam of ice, behind which water pools. The pooling water can back up under the roof covering and leak into the attic or along exterior walls.

The right weather conditions for ice dams is usually when outside air temperatures are in the low 20 degrees (F) for several days with several inches of snow on the roof.

Research shows keeping the attic air temperature below freezing when the outside air temperature is in the low 20s can reduce the occurrence of ice dams. Research has shown sun exposure in the winter has little effect on attic air temperature. Warm air from living spaces below penetrating into the attic is usually the culprit in the formation of ice dams.

Attic Condensation

Condensation of water vapor on cold surfaces in attics can cause attic wood products to rot, which can lead to costly repairs. Condensation typically occurs when warm, moist air migrates into the attic from living spaces below. Building codes have some requirements that attempt to prevent the problems of ice dams and attic condensation. But codes do not address all the issues, and many houses are built without following building codes.


What Not To Do

Source: Servpro, 1-800-293-9555