Ice Dams

A condition which can occur with snow and freezing conditions. When snow or ice melts on a roof over a heated or partially heated attic space, the melting water may refreeze over an unheated areas such as a roof overhang. This re-frozen water may create a "dam" and allow additional melt water to back up under shingles and cause leaks.(See:Illustration "A").

Solutions include: proper roof venting and insulation (See: illustration "B"), membrane roofing or roofing underlayment, and heat tapes.

Once an ice dam occurs, remedies are difficult and or dangerous. Working on a frozen roof should be avoided, as should the use of any open flames. The use of hot water to melt the ice may help, it may also increase the amount of leakage.

Ice Dams

Illustrations are from Wood-Frame Construction by L.O. Anderson - Agriculture Handbook #73 p. 72.