Roof decking material estimate
Roof Sheathing Calculator
Estimate plywood or OSB roof sheathing sheets from roof dimensions, sheet size, waste allowance, panel price, H-clips, and roofing nails. Use it before a roof deck repair, shed roof, garage roof, porch roof, or full sheathing order.
How to use the roof sheathing calculator
- Measure the roof width along the eave and the sloped distance from eave to ridge.
- Enter the number of matching roof planes. A simple gable roof usually has two.
- Add extra roof sections such as porches, dormers, or lean-tos if they are not included in the main rectangle.
- Choose the sheet size, waste allowance, sheet price, clip estimate, and nail estimate.
The calculator estimates total roof deck area, area after waste, plywood or OSB sheets to buy, H-clips, nails, nail boxes, and sheet cost.
Roof sheathing estimate example
For a 40 ft wide gable roof with two 16 ft sloped roof planes, the measured deck area is 1,280 square feet. With a 12% waste allowance and standard 4×8 sheets, the project needs about 45 sheets of roof sheathing.
Simple rectangular roofs usually estimate cleanly. Hip roofs, valleys, dormers, skylights, chimneys, and repairs around damaged decking can raise waste and labor time.
Roof sheathing FAQ
How many sheets of plywood do I need for a roof?
Divide the roof deck square footage by the sheet coverage, then add waste. A 4×8 sheet covers 32 square feet, so 1,000 square feet of simple roof area needs at least 32 sheets before waste and 36 sheets with a 10% allowance.
Should roof sheathing be plywood or OSB?
Both plywood and OSB are commonly used for roof decking when the panel thickness and span rating match the roof framing and local requirements. Availability, price, exposure conditions, and builder preference often decide the choice.
What thickness roof sheathing do I need?
Common residential roof sheathing thicknesses include 7/16 inch OSB and 1/2 inch plywood, but the correct thickness depends on rafter or truss spacing, roof load, panel span rating, and local code.
Do I need H-clips for roof sheathing?
H-clips may be required or recommended on unsupported panel edges between rafters or trusses, especially with certain spans and panel thicknesses. Confirm with your local code, plans, or inspector.
How much waste should I include for roof decking?
Use about 10% for a simple rectangular roof and more for roofs with valleys, hips, dormers, chimneys, skylights, or small repair patches. If in doubt, one or two spare sheets can prevent a second materials run.