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Preventing Roof Ice Dams

Preventing Roof Ice Dams

A snow-covered roof with icicles hanging off.

About Ice Dams

Roof ice dams occur in climates with freezing temperatures and significant snowfall. When the temperature in the attic is above freezing, snow on the roof melts and runs down the sloping roof. When the snowmelt runs down the roof and reaches the colder eaves (overhang) and gutters, it refreezes.

After several days of melting-freezing cycles, the freezing snowmelt builds up and forms a dam of ice, causing water to pond. The ponding water can back up under the roof shingles until water enters the attic and eventually damages interior ceilings, walls, and contents along the exterior walls.

Research has shown sun exposure in the winter has little effect on attic air temperature. Warm air from living spaces below penetrating into the attic is usually the culprit in the formation of roof ice dams.

The presence of significant icicles along the gutter or eaves may be an indication of roof ice damming.

Preventing Roof Ice Dams

There's no way to guarantee an ice dam will not damage your home, but you can reduce the likelihood of an ice dam forming in the first place:

  • Thoroughly clean all leaves, sticks, and other debris from rain gutters and down spouts. This allows melting roof snow to flow into gutters and through down spouts.
  • Strive to keep snow on your roof to a minimum. Long-handled devices called "roof rakes" let you stand on the ground and pull the snow off the roof. Keeping heavy snow loads off your roof reduces the chances for both ice dam formation and roof failure due to the weight.
  • Keep gutters and down spouts clear of snow and icicles all winter.
  • Evaluate the insulation and ventilation in your attic. Attic insulation should have an R-value of at least R-30 (R-38 is preferable in northern climates). In addition, good airflow from under the eaves or soffit area along the underside of the roof and out through the roof vents is essential. The insulation prevents heat loss from the interior of the home. The venting allows the attic air to stay cold enough to prevent or minimize the freeze/thaw cycle on the roof. Consult a reputable roofing and/or insulation contractor about these improvements.