An ice dam is a problem of house and building maintenance on sloping roofs in cold climates. Ice dams on roofs form when accumulated snow on a sloping roof melts and flows down the roof, under the insulating blanket of snow, until it reaches below freezing temperature air, typically at the eaves. When the melt water reaches the freezing air, ice accumulates, forming a dam, and snow that melts later cannot drain properly through the dam. Ice dams may result in leaks through the roofing material, possibly resulting in damaged ceilings, walls, roof structure and insulation, damage or injury when the ice dam falls off or from attempts to remove ice dams.
The melting of roof snow comes from two reasons: Heat from inadequate roof insulation and heat leaks, and inadequateventilation. This condition is called a warm roof and the heat conducted through the roof melts snow on those areas of the roof that are above heated living spaces, but the snow does not melt on roof overhangs. Ice Dams and related leaks are not the result of faulty roofing material.]Also, a small amount of ice damming can occur from the normal freeze-thaw cyclemelts snow on warm or sunny days. This snowmelt continues to run down the roof on cold nights and freezes when it contacts the cold air