Ice Dam Prevention

As winter advances through cycles of freezing and thawing, buildings and homes experience ice buildup and roof damage. In general, ice dams are formed when attic heat moves up to warm the roof and melts snow at or near the ridge. Snow melts, runs downward and hits the edge of the cold roof, resulting in re-freezing snow.  These cycles cause ice to accumulate and back up under shingles. Damage appears in the form of soaked insulation, stained, cracked and damaged sheet rock, damp, smelly, rotting wall cavities and stained, blistered and peeling paint.

Preventing Ice Dams

To prevent an ice dam, don’t heat the roof, keep it cold. That way, the snow on the roof eventually dissipates without making large amounts of meltwater. The underside of the roof deck should not exceed 30 F. The best way to maintain low temperatures is by ensuring that there is adequate insulation and sealing gaps that let warm air pass into the attic from the house. The attic must also be ventilated, so that cold air is introduced into it and heated air escapes rapidly. Increased insulation in an attic will help to prevent ice dams. First, insulate the areas between the roof rafters. It is important to keep an air space between the roof deck and the insulation in order to prevent a condensation buildup that can delaminate the roof deck. Prior to insulating, install polystyrene rafter air channels, which are available at home centers.  If there’s a hatchway into the attic, build a cover for it out of rigid poly-styrene insulation.

If the gable and ridge vents do not generate sufficient air movement to dissipate the heat, you will need a motorized vent at one end of the attic to exhaust the heat, and an adequately sized vent on the opposite end of the attic to draw in cold air from the outside.