An analysis of rain-on-snow loads for building roofs is presented. Surcharge loads on building roofs due to rain-on-snow events are functions of roof geometry, rainfall and snowpack characteristics. The current rain-on-snow surcharge specified by ASC 7-95 is 5 psf for roofs with a slope less than 1/2 on 12 for locations where the ground snow load p_g is 20 psf or less. This provision is based to a significant extent upon engineering judgement. A review of rain-on-snow case histories as well as statistical analyses of precipitation data is presented herein. Based upon this new information, simple procedures are suggested for incorporating the effects of rain-on-snow.
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