Roof Load Capacity Calculator

Dead Load, Live Load and Total Roof Weight in PSF

Roof loads are measured in pounds per square foot, and the difference between roofing materials is far larger than most people expect. A single ply membrane weighs about 1.2 psf and a metal panel around 1.5, asphalt shingles run 2.5 to 4.5 depending on grade, and concrete or clay tile reaches 9 to 12 — which is why switching from shingles to tile is a framing decision rather than a finish decision. This calculator sums the covering (multiplied by the number of existing layers), the sheathing, a framing and underlayment allowance, and an optional solar array at roughly 4 psf including racking, then adds your snow or live load to produce the combined load in psf and the total weight in pounds across the whole roof. It compares the live load against the design value you enter so you can see whether margin remains. It is a planning tool for the conversation with a structural engineer or solar installer, not a structural analysis, and it does not check your rafter size, span or grade.