A Climatological Measure of Extreme Snowdrift Loading on Building Roofs

Abstract

A physical model of snow transport and deposition is used in combination with historical climatological data to derive a climatological measure of extreme snowdrift loads on building roofs. The snowdrift metric used relies on hourly wind speed, temperature, and weather occurrence data and daily observations of snow water equivalent, snowfall, and snow depth. The model is applicable to both roof steps and gable roofs. On average, the maximum drift surcharge corresponds to 10%–20% of the snow on the upwind roof snow source area. There is some degree of spatial variation in this maximum drift surcharge. Values range from about 3% at stations that receive minimal snow to a maximum of 24% in the northern plains and eastern Great Lakes regions of the United States. The amount of drifting is strongly influenced by wind direction. For instance, under easterly winds, the drift-load ratio averages only 3% over all stations. These findings are in general agreement with current building-code provisions for roof steps but indicate that existing provisions for gable roof drifts may be too conservative.