Ice Dams And Attic Condensation

Feb 14, 2011

By Staff writer State Farm™ Employee

While stopping a leak or repairing a hose down in the basement might be fairly straightforward, ice dams and attic condensation, two forms of water damage typical to cold climate homes, are a little more complicated and a little trickier to fix. And since many homeowners aren't frequent visitors to their own attics in the frigid winter months, water damage on the top floor might catch you off guard.

What are ice dams? What causes attic condensation? And if you’ve got either, what can you do?

Ice Dams

When the temperature in your attic is above freezing, snow on the roof will likely melt. When the snowmelt runs down the roof and hits the colder eaves, it refreezes, especially if the temperature drops again.

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

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

Attic Condensation

Condensation of water vapor on cold surfaces in attics can cause wood to rot, which can lead to costly repairs. Condensation typically occurs when warm, moist air migrates into the attic from living spaces below. Research indicates unusually high humidity in the home's living spaces is strongly associated with attic condensation problems.

Prevention

Building codes have some requirements that attempt to prevent the problems of ice dams and attic condensation. But codes don’t address all the issues, and many houses are built without following building codes. First and foremost, it’s your builder or designer's job to understand the relationship of humidity and air movement when designing and constructing the house so these problems don't occur.

Nevertheless, there's more you can do. Here are a few simple steps that can help prevent ice dams and condensation in your attic:

  • Prevent warm, moist downstairs air from infiltrating the attic by appropriately insulating your attic’s floor and using a dehumidifier to control water vapor.
  • Seal all openings that would allow vapor to rise into the attic. Avoid designing ceiling mounted fixtures below the attic that create the need for holes in the drywall or plaster ceiling. If this cannot be done, seal around all penetrations to make them airtight. Ceiling-mounted light fixtures and ceiling fans have electrical junction boxes mounted flush in the ceiling – these often have a number of holes in them that need to be sealed.
  • 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.
  • Provide good attic ventilation to replace warm air in the attic with cold outside air.
  • Consult a professional for the best way to avoid ice dams and water damage in your home.

What Not To Do

While it might be tempting to try a quick-fix to break up that ice dam, don’t get too eager; not only is it dangerous on your roof, but you can also cause a lot of damage, especially in the colder months. Here are some things to keep in mind:

  • Do not routinely remove snow from the roof or attempt to “chip away” the ice of an ice dam. It will likely lead to shingle damage.
  • Do not install large mechanical equipment or water heaters in attics, especially in cold climates. Not only do they present an unwelcome fire hazard, but they’ll also increase the temperature in your attic.
  • 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. Runoff that contains high concentrations of these chemicals can damage nearby grass and plants.
  • Keeping the gutters clean of leaves will not necessarily prevent ice dams. However, clean gutters can help keep them from overflowing and spilling rainwater next to the house.
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