Roof sheathing, also called roof decking, is the structural layer of plywood or OSB (oriented strand board) panels fastened directly to your roof's rafters or trusses. It's the foundation everything else — underlayment, shingles, flashing — is installed on top of.
Why Sheathing Matters
Sheathing isn't visible once a roof is finished, but it's what gives shingles something solid to grip and what keeps the roof structurally sound under wind and weight loads. If sheathing is rotted, delaminated, or sagging, no amount of premium shingle can compensate for it.
Common Sheathing Materials
- OSB (oriented strand board): the most common choice in new construction today, made from compressed wood strands.
- Plywood: thin layers of wood veneer glued together; historically the standard, still widely used and preferred by some builders for its moisture resistance.
Signs Your Sheathing May Need Attention
- Soft or spongy spots when walking the roof
- Sagging areas visible from the ground or attic
- Water stains or daylight visible through the roof deck from inside the attic
- Missing or curling shingles concentrated in one area, often a sign of decking movement underneath
Sheathing and Your Roof Replacement
Whenever we replace a roof, we inspect the decking underneath once the old shingles come off. If any sections are rotted or damaged, we'll show you before replacing them — this is one of the most common reasons a final roofing bill can differ from the initial estimate, and it's something we always walk homeowners through directly rather than surprising you with it.
