This tool is critical for anyone building in the mountains or the north. It visualizes the difference between Ground Snow Load (what the weatherman says) and Roof Snow Load (what your rafters actually feel).
It features a “Snow Shedding Simulator” that demonstrates how increasing your roof pitch can drastically reduce the weight on your structure by allowing snow to slide off before it accumulates to dangerous levels.
Snow Load Calculator
Ground Load vs. Roof Load: Pitch matters.
Check your local building codes.
Designing for the White Stuff
Building codes allow you to reduce the snow load calculation for roofs steeper than 30 degrees (approx 7:12 pitch). If your roof is slippery (metal) and steep (12:12), the snow slides off immediately, drastically reducing the weight your rafters need to hold.
Ground Load (Pg) is the weight of snow on the ground.
Roof Load (Ps) is the actual weight on your house.
Formula: Ps = 0.7 × Pg × PitchFactor. Even flat roofs get a 30% reduction because wind blows some snow away.