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The Impact of Ice

Did you ever wonder where icicles come from? Did you know that if you have icicles you might have an ice dam as well? And if you have an ice dam, you may soon be fighting a roof leak.

When snow falls on a roof, it seals the roof, which becomes almost airtight. As the house is warmed to a nice toasty temperature, heated air escapes into the attic. As the attic gets warmer, it melts the snow atop the roof, and water rushes downward toward the overhangs. The moment the liquefied snow hits a cold overhang it begins to freeze. The water that freezes after it rolls over the edge becomes icicles.

Water that freezes before it rolls over the edge builds up to create a barrier known as an ice dam, which becomes larger and larger as runoff continues to freeze. Finally, the ice on the overhang widens to the point where it reaches the edge of the attic. At this point, the water remains liquid and the ice dam causes it to back up over the attic where it can leak into the home.

All too often, this is precisely what happens-water held back by the ice dam backs up and leaks into the home. There are other negatives about ice on your roof. Ice buildup can damage rain gutters, causing costly repairs. By preventing ice buildup, you might be able to save your house from being flooded during a freeze and add a little life to your gutters, as well.

To prevent an ice dam, you need to keep the attic cold. Not the house-the attic. If the attic is cold, the snow on the roof won't melt, and ice dams won't form. Here's how to make it happen:

  • Don't close off eave and roof vents during the winter. This traps the warm air that melts snow on the roof.
  • Fill all penetrations between the living space and the attic area with foam sealant. You can buy it in a spray can. Look for penetrations in the ceiling in the following places (many may be hidden beneath attic insulation): plumbing vents, ventilation ducts, heat registers, electric wiring, and ceiling light fixtures.
  • Don't caulk around furnace flues. A flue that contains hot gasses should not come into contact with combustibles such as wood or foam sealant. Contact your local heating or sheetmetal contractor and have a metal draft stop installed. It can be sealed to the pipe and the house frame without creating a fire hazard.
  • Check your attic insulation. Be sure that your attic insulation is loose (as opposed to compacted) and that there is a more than sufficient amount up there. Check with your local utility company. Most offer free energy audits. Your local building department is another inexpensive inspection alternative.
  • Consider installing an eave-heating device such as heating tape or heating wire. They prevent water from freezing on your eave. Eave heaters operate on extremely low voltage, making them inexpensive to operate.
  • Install special metal flashings at problem eaves. Ice doesn't stick to the metal as readily as it does to most types of roofing. The nice thing about metal flashings is that they can be made to order by your local heating or sheetmetal contractor. You may be able to save money by looking for a product at your local home center known as "Ice and Water Shield."