How this calculator works
For vertical snow depth, mass per horizontal area is bulk density times depth; multiply by standard gravity for pressure. Roof pitch changes sloped surface area but does not reduce the weight of an entered vertical snow column. Density presets are illustrative points within broad published ranges. Design mode evaluates entered factors using the legacy ASCE 7-16 balanced equation or the Canadian factor equation; it does not supply local climate values, current-code risk coefficients, drifting, sliding, partial loading or load combinations. Capacity mode needs an independently assessed capacity and does not infer one from climate loads.
Formula
pressure = density x 9.80665 x vertical depth; total mass = pressure x horizontal area / 9.80665; legacy US ps = 0.7 Ce Ct Is pg Cs; Canadian S = Is [Ss Cb Cw Cs Ca + Sr].
Worked example
A 0.1 m vertical layer at 100 kg/m3 imposes 98.0665 Pa. Over 100 m2 its mass is 1000 kg. The legacy US expression with pg = 2 kPa and all entered factors equal to one gives 1.4 kPa.
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Frequently asked questions
Can this tell me whether a roof is safe?
No. Roof capacity requires structural assessment, and real snow may form uneven drifts or accumulate rain and ice. Do not treat a design climate load as existing roof capacity.
Why are there no city selectors?
Design loads depend on code edition, location, elevation and the authority having jurisdiction. Enter verified climate values and coefficients for the project instead of relying on an unsourced city table.
Does pitch automatically shed the snow?
No. Actual shedding depends on surface, temperature and obstructions. In design mode enter a verified slope factor; in measured-depth mode the entered vertical snow layer retains its full weight.