Loads due to Drifted Snow

Roof failures due to snow loads are often the result of heavy drifts rather than uniform snow loads. Codes and standards such as Standard A58.1 of the American National Standards Institute (ANSI) and the National Building Code of Canada contain procedures for estimating snow loads on basic structures only. An understanding of elementary fluid mechanics and snow accumulation phenomena allows a designer to predict regions of potentially heavy snow loading in situations not covered by the codes. Several basic principles are presented and illustrated by examples of air flow around commonly shaped structures and the regions of snow accumulation. Modeling of snow drifting supplies qualitative information on snow accumulation in complex situations; advantages and limitations are examined.