Calculating Roof Pitch for Snow Load

Proper roof geometry is essential for managing snow accumulation in colder climates.

The 30-Degree Rule

• A pitch of 30 degrees or steeper allows heavy snow to slide off naturally, reducing the weight on the structure.
• Shallower roofs trap snow, creating a significant load that can exceed the design limits of standard rafters.
• Steep pitches also improve drainage, which prevents ice dams from forming at the eaves.

Material Selection

• Continuous roof decks provide a uniform surface that helps snow slide off more easily than trusses.
• Proper ventilation under the roof deck keeps the surface temperature above freezing.
• Installing snow guards can be beneficial on steep roofs to prevent large slabs from sliding onto walkways.

Engineers use specific load tables to determine the maximum allowable snow weight for a given roof geometry.