Flat Roof Snow Loads

Section 7.3 in ASCE 7-22 provides for calculation of the flat roof snow load and prescribes a minimum roof snow load. Areas with infrequent snowfalls and small accumulations tend to have higher ground-to-roof conversion factors than colder areas with substantial ground snow accumulation. The exposure factors are a function of the terrain or surface roughness category and the location of the structure with respect to various obstructions within the given surface roughness category. The intent of the ASCE 7 thermal factors is to quantify the differences in ground-to-roof conversion factors specifically due to heat loss through the roof layer. The roof snow loads prescribed in ASCE 7-22 are based on the ground snow load, modified by various exposure and thermal factors. However, there are other surfaces such as near ground decks and roofs of subterranean spaces for which the usual building related exposure and thermal factors do not apply.