Eave Ice Dams

Abstract

Water seepage into interior spaces and the resultant staining of wall and/or ceiling surfaces is a common problem with eave ice dams. If the outdoor temperature is below freezing, the roof is poorly insulated, and if the roof snow layer is thick enough, the temperature at the bottom of the snow will be at freezing. A portion of the thermal energy goes into melting some of the roof snow, that is, meltwater is generated which flows downslope toward the eaves. Some of the meltwater refreezes at the cold eave, forming an ice dam. The potential for water seepage is related to the horizontal extent of the ice dam. Mitigation usually involves placing an impermeable “ice and snow guard” layer for some distance from the eave. This paper presents information on the horizontal extent of expected eave ice dams with various returns period for 15 U.S. cities. In addition a correlation between ice dam size and the 50-year ground snow load is presented which allows one to estimate ice dam size for any U.S. city.