Roof Snow Load Calculator
Estimate the design flat-roof snow load and total snow weight on a roof using a simplified version of the ASCE 7 method.
About the Roof Snow Load Calculator
This calculator gives a simplified estimate of flat-roof snow load using the general form of the formula referenced by ASCE 7, the structural standard most U.S. building codes point to. It converts a ground snow load into the design load your actual roof needs to support, then totals the weight of snow the roof area could be carrying at that load.
Formula: Flat Roof Snow Load (Pf) = 0.7 × Ce × Ct × Is × Pg, where Pg is ground snow load, Ce is the exposure factor, Ct is the thermal factor and Is is the importance factor; Total Snow Weight = Pf × Roof Area
This simplified version omits the roof slope factor (Cs) used for steep roofs and the minimum load provisions of the full ASCE 7 standard, so treat it as a planning estimate only. Always confirm the ground snow load and final design values with your local building department or a structural engineer before finalizing roof framing — undersized snow load assumptions are a common cause of roof failure in heavy snow regions.