Snow Load Calculator

The slope factor Cs stays at 1.0 for any roof up to 30°, then declines linearly down to zero at 70°, reflecting the physical reality that snow simply slides off a steep enough surface rather than accumulating. This calculator only models the warm-roof version of that reduction, so it applies regardless of your thermal factor input — a cold or unheated roof, which ASCE 7 treats less generously for slope reduction, isn't distinguished here.

No — this calculator uses a simplified 1.5× multiplier on the flat roof snow load rather than the full ASCE 7 leeward-drift geometry, which actually depends on the upwind fetch length and the height of any adjacent roof step or parapet. Treat the reported drift load as a rough placeholder for typical cases, and calculate the real drift formula by hand for any roof condition where drift is a genuine design concern (like a lower roof next to a taller adjacent structure).

That 0.7 coefficient reflects the statistical relationship in ASCE 7 between the 50-year ground snow load and the generally lighter load that actually accumulates on a roof, which loses some snow to wind and thermal effects that the ground doesn't experience. It's a baseline reduction applied before the exposure, thermal, and importance factors adjust the load further for your specific site and building.

It's one of three multipliers directly scaling the flat roof load, ranging from 0.7 for a fully exposed, wind-scoured site (like an open ridge) up to 1.2 for a sheltered site in dense forest — nearly a 2x swing between the extremes. Since Ce multiplies linearly against ground snow load along with thermal and importance factors, choosing the wrong exposure category for your actual site can shift your design snow load by close to that same proportion.