FEMA: Snow Load Safety Guidance

FEMA: Snow Load Safety Guidance

Key Safety Issues and Risks Snow accumulation in excess of building design conditions can result in structural failure and possible collapse. Structural failure due to roof snow loads may be linked to several possible causes, including but not limited to the following: • Unbalanced snow load from drifting and sliding snow. When snow accumulates at different depths in different locations on a roof, it results in high and concentrated snow loads that can potentially overload the roof structure.

• Rain-on-snow load. Heavy rainfall on top of snow may cause snow to melt and become further saturated, significantly increasing the load on the roof structure.

• Snow melt between snow events. If the roof drainage system is blocked, improperly designed or maintained, ice dams may form, which creates a concentrated load at the eaves and reduces the ability of sloped roofs to shed snow. On flat or low slope roof systems, snow melt may accumulate in low areas on roofs, creating a concentrated load.

• Roof geometry. Simple roofs with steep slopes shed snow most easily. Roofs with geometric irregularities and obstructions collect snow drifts in an unbalanced pattern. These roof geometries include flat roofs with parapets, stepped roofs, saw-tooth roofs, and roofs with obstructions such as equipment or chimneys. Unbalanced Snow Load from Drifting and Sliding Snow on Reside

Click here for the pdf from FEMA providing more information on Snow Load Safety.