13th Conference on Applied Climatology and the 10th Conference on Aviation, Range, and Aerospace Meteorology

Thursday, 16 May 2002: 11:00 AM
Climatic probabilities of snow drift loading on gable roofs
Arthur T. DeGaetano, Northeast Regional Climate Center, Cornell Univ., Ithaca, NY; and M. J. O'Rourke
Poster PDF (590.8 kB)
Due to their geometry, gable (peaked) roofs are likely to experience enhanced snow drifting on their leeward slopes. Currently building codes prescribe a uniform drift surcharge for roofs with a moderate slope, while a triangular surcharge (small near the peak and large at the eave) is suggested for small roof slopes. There has been considerable debate in the civil engineering community as to how to best quantify this drift surcharge as a function of the ground measured snow load. Based on the literature and water flume simulations an equation characterizing snow transport and trapping across a gable roof is formulated. As this equation is driven solely by wind speed, it can be used in conjunction with the hourly climate record to compute series of annual maximum snow drift weights. This paper describes the development of a snow drift metric and the resulting snow drift weight climatology. Here the drift metric is a function of the amount (weight) of driftable snow on the windward roof, wind velocity, and the duration of wind speeds above the drifting threshold. The computation requires an hourly budget of driftable snow be maintained for the source roof. This budgeting scheme; which is based on time since new snowfall, temperature, and non-frozen precipitation occurrence; is also discussed. Snow drift metrics are calculated for a network of approximately 50 U.S. first order stations and used to compute 50-year return period snow drift weight surcharges. The spatial pattern of these values will be discussed as will their dependence on the orientation of roof slope with respect to the prevailing wind direction.

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