An ice dam is a build up of ice and water that works
its way under shingles. When snow from the peak melts
(caused by warm spots in the attic or the sun), water
slowly runs down the roof. When the water hits a
cold spot on the roof (usually at the eaves), the
water refreezes. As more melting water hits the cold
spot, it begins to build up and eventually works
its way underneath shingles and sheathing.
Sealing
warm air leaks from interior rooms to the attic
is probably the most effective way to prevent
ice dams. These warm air leaks are typically found
around vent pipes, exhaust fans, chimneys, attic
hatches, wall and ceiling framing joints, wiring
and lighting fixtures.
