Some roofing configurations are more prone to ice damming problems than others. Ice damming occurs when snow and ice collect in a certain area of the roof (often the eaves and valleys). Melting snow on the upper portion of the roof cannot drain properly as it is trapped behind the ice dam (see Figure 5). If the dam is large enough and sufficient water collects, it will back up under the shingles and leak into the eaves or worse, into the exterior walls or the building's interior.

Solutions

Effective solutions to ice damming problems are, increased attic insulation and ventilation. These two measures reduce the air temperature in the attic so that there is less tendency for snow to melt over the heated portions.

Mid-winter clearing of snow from eaves, valleys, skylights, chimney and roof vents before ice damming occurs is recommended. Also, at the time of the re-roofing, eaves protection (ice and water shield) should be provided beneath the shingles for a distance of at least 2 1/2 feet beyond the interior of the exterior wall.