What thickness roof sheathing should I use?

Use 7/16-inch OSB for 16-inch on-center rafter or truss spacing. Step up to 1/2-inch OSB or CDX plywood for 24-inch spacing. In heavy snow load areas or for tile roofing, 5/8-inch or 3/4-inch panels may be required. Check the panel span rating stamp to confirm it matches your framing spacing.

How do I calculate roof area?

Multiply your building footprint area by the roof slope factor. Common slope factors: 4/12 pitch = 1.054, 6/12 = 1.118, 8/12 = 1.202, 10/12 = 1.302, 12/12 = 1.414. For hip roofs, add 10% to the calculated area for the additional cuts and waste at the hip lines.

How many sheets of roof sheathing do I need?

Divide the total roof area by 32 sq ft per sheet and add 10% for waste. A 1,500 sq ft roof needs about 47 sheets net, or 52 with waste. Hip roofs and complex geometries generate more waste (15-20%) due to angled cuts along hips and valleys.

What are H-clips and do I need them?

H-clips are small galvanized metal clips that slide between adjacent sheathing panel edges at mid-span between rafters or trusses. They support the panel edges and prevent sagging under load. H-clips are required for 24-inch framing spacing with 7/16-inch or 1/2-inch panels and are generally good practice for any roof.

OSB vs plywood for roof sheathing — which is better?

Both are code-compliant. OSB is 20-30% less expensive and the most widely used. Plywood handles moisture better and is preferred in high-humidity climates or where extended weather exposure during construction is expected. For the best performance, CDX plywood or ZIP System roof sheathing panels are the top choices.

Can I install roof sheathing in the rain?

Avoid installing sheathing in active rain, as wet surfaces create a slip hazard and panels can absorb moisture that leads to mold. If panels do get wet during construction, allow them to dry before applying underlayment. Exposure 1-rated panels can handle brief weather exposure without structural damage.

Roof Sheathing Calculator

How many OSB sheets to sheathe my roof? Free roof decking calculator for 1200×2400 mm panels — factors in roof pitch and waste.

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Enter Your Measurements

How to Use This Calculator

1Calculate roof area (slope length × roof length × 2 for gable, or use a slope factor).
2Click Calculate — includes H-clip count.

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About This Material

Roof sheathing creates the structural deck that supports roofing underlayment, shingles, and all roof loads. The standard material is 7/16-inch OSB for 16-inch rafter or truss spacing, and 1/2-inch OSB or CDX plywood for 24-inch spacing. Panels are 4x8 feet (32 sq ft each) and are installed horizontally starting from the eave, with staggered end joints between rows. H-clips — small metal clips inserted between panel edges at mid-span — are required wherever unsupported panel edges span between rafters or trusses to prevent sagging under load. OSB roof sheathing costs $15 to $30 per sheet, while CDX plywood runs $25 to $45. In regions with frequent wind-driven rain, radiant barrier sheathing (OSB with a reflective foil face) helps reduce attic heat gain. Always use Exposure 1-rated panels since roof sheathing may be exposed to weather during construction. The nailing schedule is critical for wind uplift resistance — 8d nails at 6 inches on edges and 12 inches in the field.

Next Steps:

Shingle Calculator →Roofing Underlayment Calculator →Roof Area Calculator →

Roof Sheathing Calculator

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About This Material

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