Decking (or sheathing) is the plywood or OSB skin nailed to your rafters — the surface your roof is actually attached to. If it is rotten, delaminated, or too thin for modern fastening schedules, sections must be replaced during your re-roof. It is the single most common "surprise" line item in roofing, and it cannot be counted from the ground or from a satellite.
What it costs
Published guides put installed decking replacement at $65 – $95 per 4×8 sheet, including material, cutting, and fastening. A typical roof needs anywhere from zero sheets (sound deck) to 10–20% of its surface replaced on leak-prone older homes.
How to keep it honest
- Per-sheet pricing in writing. Agree the per-sheet rate in the contract before tear-off, so there is nothing to negotiate with your roof open.
- Photo documentation. Good roofers photograph every replaced sheet. Ask for it.
- Budget a contingency. On homes over 25 years old in wet climates — the Pacific Northwest especially — budgeting 10% of roof area as potential decking is a reasonable planning allowance, which is one reason our estimates are ranges.
Our real-prices step states this to both sides: roofer prices are good-faith and subject to on-site verification of decking and layers. That sentence protects you from lowball-then-surprise bidding as much as it protects the roofer.
Run your own numbers: the satellite estimator and the roof cost calculator are both free, and both use the published dataset on our methodology page.