What thickness roof sheathing should I use?

7/16" OSB for 16" OC rafters/trusses. 1/2" for 24" OC. CDX plywood is a premium alternative with better moisture resistance.

How do I calculate roof area?

Roof area = plan footprint × slope factor. Slope factors: 4/12 = 1.054, 6/12 = 1.118, 8/12 = 1.202, 10/12 = 1.302, 12/12 = 1.414.

Roof Sheathing Calculator

Calculate how many 4x8 OSB sheets you need to sheathe your roof deck.

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Enter Your Measurements

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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 (7/16" or 1/2" OSB or 1/2" CDX plywood) creates the structural deck for roofing materials. H-clips are required between unsupported panel edges to prevent sagging.

Installation Tips

•Start from the eave, working toward the ridge.
•Stagger end joints between rows.
•Leave 1/8" expansion gaps at all edges.
•Install H-clips at mid-span between rafters/trusses.

Common Mistakes to Avoid

Forgetting H-clips — required for 24" OC framing.
Not staggering end joints.
Using interior-rated OSB in wet climates — use Exposure 1 or exterior rated.