Snow load design criteria

Based on the 2014 Oregon Structural Specialty Code

Minimum roof snow load

The minimum design roof snow load for all structures in Oregon is 20 pounds per square foot (psf). This may not be reduced for slope or any other conversion factor, and may be only modified where applicable by a rain-on-snow surcharge. (Oregon Structural Specialty Code (OSSC), Section 1608.1)

Rain-on-snow surcharge

A 5 psf rain-on-snow surcharge will be added to the minimum design roof snow load if either of the following conditions exist:

  • All roofs with a slope of less than 4.76 degrees (1 on 12 pitch)

or

  • Roofs of any slope that constrain runoff, i.e., any roof where the drainage system is impeded by parapets, or any other physical obstructions capable of accumulating more than 1 inch of standing water on any part of the roof when the primary or the secondary (drains or scuppers) means of drainage is blocked by debris, snow or ice. (Structures with a continuous gutter at the low point eave or a comparable system are not be considered as having constrained runoff.)

Snow Load Analysis for Oregon, Structural Engineers Association of Oregon

Ground snow load

To find the ground snow load used to determine the design snow loads for buildings and other structures, refer to the online lookup tool or the online map published by the Structural Engineers Association of Oregon (SEAO). The design roof snow load may not be less than 20 psf with rain-on-snow surcharge as applicable.

For more information

Design snow loads for buildings and other structures are determined based on the American Society of Civil Engineers 7-10 Standard, Minimum Design Loads for Buildings and Other Structures, Chapter 7. More information is available from the State of Oregon Building Codes Division, Statewide Alternate Method No. 15-02.