Roof Load Calculator

How It Works

Roof loads have two components. Dead load is the weight of permanent materials — roofing, deck, framing, insulation. Live load is temporary weight — snow, rain, workers, and equipment. Building codes require roofs to handle both simultaneously. Most residential trusses are designed for 20-25 psf dead load and 20-40 psf live load. When switching from light materials (asphalt at 2.5 psf) to heavy ones (tile at 10 psf or slate at 12 psf), the added 7-10 psf may exceed the original design. Always consult a structural engineer before installing tile or slate on a structure designed for shingles. Adding a second layer of shingles adds about 2.5 psf.