Beware of Snow Buildup On Open Roof Areas
An important and frequently overlooked requirement for checking snow loads on open roof systems such as pergolas, trellises, and mechanically louvered roofs is the snow ‘buildover’ effect.
This occurs when the snow accumulates on open patio roof components to the point where it builds ‘up and over’, touching the snow on the adjacent roof component.
ASCE 7-16 & ASCE 7-22 section 7.13.3 state that when the spacing between open components is less than the buildup height of the snow, an additional uniform cornice load shall be applied to the space in between.
This is illustrated on ASCE figure 7-13 shown below, along with some illustrative examples.
Engineers must consider this loading when evaluating the design capacity of open roof patio enclosures, as well as all uplift, gravity, and lateral forces, snow drift, seismic, and dead load considerations & combinations.
Figure from ASCE 7-16 & 7-22 Illustrating snow buildup on open roof areas
Illustrative Examples
The engineers at Engineering Express are experts in this field and frequently design open patio structures for review by project engineers, architects, and plan reviewers across the US.
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Last Update: December 4, 2024