Ice Dams on Roof

ICE DAMS ON ROOF Snow blanket Melted snow (water) Ice dam Stained and Wet (ineffective) insulation Overloaded cracked plaster rain gutter Void due to sagging Icicle insulation; damp rotting walls Frozen sidewall Wet (ineffective) ice formations insulation Stained, blistered, Stained, blistered, and and peeling siding peeling wall paint Ice dams form when heat enters an attic and melts snow on the roof. The melted snow (water) runs down the roof, under the blanket of snow, to the edge of the roof where colder conditions cause it to freeze, forming ice dams. If ice dams are not removed, water may be caught behind them, forced under shingles or spill over to form icicles. This can result in costly damage to your Each year, ice dams cause millions home: wet (ineffective) insulation; stained or cracked plaster or sheetrock; damp, rotting walls; of dollars in damage to homes. and stained, blistered or peeling paint. However, if you take the right steps, you can minimize or avoid this problem. Preventing ice dams Since the basic cause of ice dams are air leaks creating warm spots on the roof, the solution is usually to maintain a cold roof. You can take three steps to achieve a cold roof: seal bypasses, insulate and ventilate. Seal bypasses Any hole, crack or crevice that allows heated air to leak through and past insulation is known as a bypass. If bypasses are not sealed before insulating, the insulation only “filters” the warm air on its way to the attic and your roof will still have warm spots. Bypasses are found: • Around light switches, outlets and light fixtures • Around chimneys and plumbing stack pipes • At the rim joist and foundation • Around bathroom and kitchen ceiling vents and any other warm exhaust equipment • Through dropped soffits (ceilings) NOTE: Recessed lights also are bypasses but, because of possible heat buildup, they should not be covered with insulation. If you can, replace with conventional lighting or a zero-clearance fixture. Continued on back Chimney Vent TOP OF AIR LEAK Plumbing stack Lighting fixture Baffle board Attic hatch Electrical outlets Fireplace Insulation over joist Vapor Furnace barrier BOTTOM OF AIR LEAK Soffit vent Air passage Proper installation of insulation is as Temporary or emergency important as R-value. In many homes the continuity of insulation is broken by pipes, measures wires, recessed ceiling fixtures, bridging and If you already have water or ice dam recessed bridging, which allows heat to enter problems, the following methods can help the attic. An attic floor with sealed bypasses but will probably have to be repeated with Attic floor and properly installed insulation will be the every winter storm. most effective. • Remove all the snow with a “roof rake.” Air barrier Warm air Ventilate Beware of icy conditions, falling snow or Despite efforts to seal bypasses, some warm ice, and overhead wires. Techniques for sealing bypasses depend on moist air from the living space may still • Steam the roof. You may want to hire a the size and accessibility of the openings. escape into the attic. Vents in the attic will professional with proper tools and Use regular caulk for small holes. Holes too help maintain a cold roof by allowing this air equipment. large or deep for regular caulk can be sealed to escape to the outside. Without adequate • You can install electric cables along the with foam caulk or void filler. Around a ventilation, water vapor can condense and eaves and in the valleys of the roof to drain metal flue and masonry chimney, seal the collect on insulation and rafters. Keep ice dams. But melting is limited to the few bypass with a sheet metal collar and high- existing vents open. Air chutes or baffle inches around the cables, and the sawtooth temperature silicone caulk. boards may be needed to maintain an open melting often causes secondary ice dams Open wall cavities and other large openings space so air can flow from the soffit area to to develop higher on the roof. Also, cables such as spaces between floor joists in attic vents high on the roof. use a great deal of energy. expansions may be sealed with air barriers While each home is unique, one square foot • Never chop ice off the shingles or use a made from rigid foam, blown foam or any of open vent is usually needed for every 300 blow torch. This could damage the roof material that provides an air barrier. Rigid square feet of attic floor space. For the best or cause a fire. materials should be cut to fit the opening air flow pattern, distribute vents equally and caulked into place. between low (inlet) and high (outlet) areas Remember, these are only temporary or Insulate on the roof. That way cool outside air will emergency measures and may only treat enter the low vents, move along the ridge sections of the roof. Extreme care should The function of insulation is to resist the rafters and exit through high vents. If you be taken to avoid damaging the shingles, transfer of heat from your living space to do not have a vapor barrier, the amount of flashing and gutters. the attic. Insulation is rated by R-value; ventilation could be doubled (up to one the higher the R-value, the better it resists square foot for every 150 square feet). heat transfer. In Minnesota, an attic floor This recommendation also applies to should have an R-value of at least 38 to 44. cathedral, flat and mansard roofs/ceilings. 612-372-4727 (1-800-245-2377) CenterPoint Energy CenterPointEnergy.com Customer Relations PO Box 59038 Minneapolis, MN 55459-0038 FPO ©2008 CenterPoint Energy 82211.

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