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The Dangers of Attic Condensation & Ice Damming and What To Do About It

About Attic Condensation

Attic condensation can cause a variety of issues in your home. These issues, if not addressed promptly and repaired properly, can be very detrimental to the structure of your house as well as the health of you and your family. Condensation during the winter months help create an environment conducive to the formation of Ice Dams, where ice and snow on the unheated edges of your roof do not melt as fast as the heated areas that cover your attic space. Once an ice dam has occurred, water tends to backup under roofing materials and infiltrate into attics and living spaces. These Ice Dam leaks account for a large percentage of roof and structural damage to homes every year. Roof leaks can also severely degrade the R value of your attic insulation as well.

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.


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 20’s 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.

About Ice Damming?

The buildup of ice and water at the eaves of a sloped roof. Melting snow on the roof refreezes at the roof overhang, causing the damming. Buildings with inadequate attic insulation or ventilation or with large roof projections beyond the exterior walls are more pronto to ice damming. View our chart below to see what ice damming is and how to prevent it.

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. 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.


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