Calculate the number of plywood or OSB sheathing boards needed to deck a roof, allowing for pitch and waste.
A pitched roof has a larger surface area than the flat footprint beneath it. We multiply the footprint by the slope factor (1 ÷ cosine of the pitch angle), then divide by the area of one 8 × 4 ft sheet and round up.
For most domestic roofs, 11–18 mm (7/16–23/32 in) OSB3 or plywood is used, depending on the rafter spacing.
Use a roof pitch calculator from your rise and run, or measure the angle directly. A common house roof is around 30–45 degrees.
Yes. Complex roofs generate more offcuts, so allow 15% waste rather than 10% if your roof has hips, valleys or dormers.
18 mm (3/4 in) OSB or plywood is common for roofs; thinner boards may be allowed at closer rafter spacing. Always check the board span rating.
Divide the sloped roof area by the sheet area (about 2.98 m² for an 8×4 sheet) and add waste. The calculator does this allowing for pitch.
Calculate roofing materials including shingles, underlayment, and ridge caps for your roof.
OpenCalculate the true sloped surface area of a roof from its footprint and pitch, in square feet, square metres and roofing squares.
OpenFind the pitch, angle, and slope of your roof from rise and run measurements.
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