Ice Dams on your mind?

Ice Dams and Attic Condensation

Two types of attic water damage are common in cold climates: ice dams and condensation of water vapor on cold surfaces in the attic.

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 ponds. The ponding 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 20s (°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... 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... Condensation typically occurs when warm, moist air migrates into the attic from living spaces below.

Prevention
Prevent warm, moist air in living spaces from infiltrating into the attic with a good air barrier and appropriate water vapor control at the base of the attic.
Provide good attic ventilation to replace warm air in the attic with cold outside air.
Provide adequate attic insulation to reduce the transmission of heat into the attic from living spaces below.
Consult a professional...

What not to Do
Do not routinely remove snow from the roof. It will likely lead to shingle damage.
Do not attempt to "chip away" the ice of an ice dam. It will likely lead to shingle damage.
Do not install mechanical equipment or water heaters in attics, especially in cold climates.
Do not use salt or calcium chloride to melt snow on a roof. These chemicals are very corrosive and can shorten the life of metal gutters, downspouts and flashings...

If ice dams are causing water damage

...In order to avoid the same problem in the future, a qualified contractor should assess the amount of attic insulation and attic ventilation (especially around where the ice dam formed), and look for holes in the air barrier between the living spaces and the attic.
If you see water staining at an exterior wall or ceiling where there is snow on the roof above it, act quickly to avoid extensive damage.
Hire a contractor to carefully remove most of the snow from the roof above the ice dam...

Source: http://www.statefarm.com/learning/loss_prevent/learning_lossprevention_icedams.asp accessed February 13, 2010 8:10p.m.