February 2010
 Ice damming begins when melted water from snow refreezes on a roof. This generally occurs near the eave of a building, although it can develop at any change in slope (such as in a valley). When more melted water backs up behind this ice dam, it seeks any weakness in the roof system and may flow under shingles, underlayment, or flashing, possibly resulting in damages to the interior of the building below.
When the accumulated water on the roof penetrates the building envelope, ice damming often causes telltale symptoms that include water leaks, water stains, and fungal growth around the exterior walls and perimeter ceilings of the affected buildings. Ice damming can often be prevented by properly ventilating the attic, so that heated air is allowed to effectively escape. Ice damming can also be prevented by insulating the ceiling so that the loss of heated air inside the building into the attic is minimized, thereby reducing the opportunity for heat to warm the underside of the roof and melt the accumulated snow. Obstructed or inadequate soffit vents can cause heat buildup in the attic above the exterior walls of the house, promoting ice damming. Click to Continue »
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