Structural snow loads

Snow loads on flat roofs are affected by local conditions, as well as the roof geometry, wind exposure and thermal environments. The dimensionless thermal factor Ct proposed by American National Standards Institute is examined in this study. Continuously monitored heat flux and temperature data for a structure with four distinct thermal environments were combined with National Weather Service data and snow core samples from the roof and ground during the winter of 1982-83. Models were developed based on these data and a standard energy balance to predict snow load for the four roof enviromnents and the ground. Ground-to-roof thermal conversion factors (Ct), both predicted and observed, were found to be a function of roof heat flux and substantially higher than those recommended by the American National Standards Institute.