An ice dam can occur when snow accumulates on the slanted roof of a house with inadequate insulation. Heat conducted through the insufficient insulation and warm air from the attic bypasses, warms the roof, and melts the snow on those areas of the roof that are above living spaces, but does not melt the snow on roof overhangs. Meltwater flows down the roof, under the blanket of snow, onto the eave and into the gutter, where colder conditions on the overhang cause it to freeze. Eventually, ice accumulates along the eave and in the gutter. Snow that melts later cannot drain properly through the ice on the eave and in the gutter, resulting in leaks to the roof space resulting in damaged ceilings, walls, roof structure and insulation.
