Case Study: Failure at an Abutting Lower Roof Due to Snowdrift

Abstract

Roof failures can occur at abutting lower roof structures which are susceptible to snowdrift loads. Snowdrift accumulation at abutting lower roofs is dependent on several factors including snow density, quantity of driftable snow, geometry of the lower and upper roofs, and wind directionality. Presented herein is a case study involving the partial roof collapse of an abutting lower roof structure as a result of snowdrift accumulation on the lower roof framing. While the authors' forensic investigation of the partial roof collapse led to the discovery of design and construction deficiencies in the lower roof framing, the authors determined that the code-prescribed design snowdrift height was less than half of the actual observed/measured height of snowdrift on the lower roof. These findings have led the authors to questions regarding the safety and adequacy of the current code-prescribed design loads as they relate to snowdrift at lower roof structures with similar roof geometries and ground snow loads to those presented in this case study.