What is an ice dam?
Ice dams are formed when the heat escaping from your house through your attic and roof melts the snow off your roof much faster than the normal outdoor conditions would. The melting snow then freezes on the eaves of the house where there is an absence of heat forming a “dam” at the eve of the roof. When additional water from melting snow runs down the roof it is unable to run off due to the “dam” at the eaves, this water backs up under the shingles and sometimes into your home especially if your roof overhang is not very wide. Homes with wide overhangs are still susceptible to ice dams but the water has a harder time backing up into the house because the ice dam forms farther away from the interior of the house. Your homes shingles are designed to be waterproof only when able to shed water completely. Ice dam conditions usually occur after a heavy snow followed by an extended period of cold weather.
A. When roofs are not adequately ventilated, they become warm. Snow melts near the ridgelines of warm roofs and the water runs down to the cooler edges of the roof and refreezes. The recurring process of snowmelt and refreeze leads to an ice dam. This dam allows water and ice to seep under the shingles, soak into the decking, and even into the house itself. Because the heat from the house melts the ice, serious leaks can occur even when the temperature is below freezing. To prevent ice dams, maintain proper ventilation in the attic to keep the roof cool. Ice and water shield, a rubber-like membrane should also be installed under the shingles at high-risk areas such as eave edges and valleys.
