Roof Decking Replacement Calculator
Decking surprise is the #1 cost variability on a roof replacement. This calculator estimates the sheet count and total cost (material + labor) for the percentage of decking you expect to replace — so you can spot a sandbagged or inflated bid.
Decking inputs
Most contractor bids quote a per-sheet replacement price assuming an unknown number of bad sheets. Get this itemized in writing. A bid that says "decking included" or quotes a flat decking allowance is hiding the variability — you can end up paying $1,000+ more (or, with an honest contractor, less) than expected.
Signs you'll need more replacement
- Visible sag between rafters — soft spots underfoot during inspection.
- Stains on the ceiling below — especially around chimneys, vents, valleys.
- Multi-decade roof age — 30+ year asphalt, 50+ year metal, 60+ year tile.
- Past leak repairs — caulk and patch over wet decking creates rot incubators.
- No vapor barrier — moist Texas attics rot decking from below.
OSB vs plywood
OSB (Oriented Strand Board)
Cheaper, lighter, and code-acceptable for most residential roof sheathing. The downside: OSB swells when it gets wet and doesn't fully recover. In a humid attic with marginal ventilation, OSB can soften over years even without a leak. 7/16″ is the most common thickness; 19/32″ is required by code in some high-wind regions.
Plywood (CDX)
Slightly more expensive, slightly heavier, but tolerates moisture cycles much better. 1/2″ is the standard upgrade; 5/8″ is required by some HVHZ codes (Florida) and is often specified in Gulf-coast hurricane zones.
How decking replacement actually plays out on a job
- Tear-off begins. Crew rips shingles and underlayment down to bare deck.
- Crew lead walks the deck looking for sponginess, soft spots, visible rot, fasteners that don't hold.
- Bad sheets are marked, removed, and replaced with new material — typically the same thickness as the original.
- Sheet count is documented; you're charged per sheet (or per the contracted decking allowance).
The contractor sandbag
Some contractors quote a flat "decking allowance" (e.g., $500 included). What you don't see: their bid assumes the allowance is exhausted and they pocket the difference if it's not. A more honest contractor itemizes:
- Per-sheet price for replacement (including labor)
- Crew documentation: which sheets were replaced, photos before/after
- Final true-up: you pay for what was actually replaced, not a flat allowance
Ask for itemized decking pricing in writing. Get the per-sheet number agreed before tear-off — not after the crew is already on the roof.
Signs you'll need more replacement than typical
- Roof age 25+ years — the longer it's been on, the more cumulative moisture exposure.
- Past leak history — caulk-and-patch repairs trap moisture under shingles.
- Visible sag between rafters — soft spots underfoot during walk-around.
- Ceiling stains below — chimney, vent, valley areas are common rot zones.
- Inadequate attic ventilation — moisture builds up, decking rots from below.
- Multi-layer roof — second layer holds heat and moisture against the first.
About this calculator
Reviewed by Eurocraft, a Texas-licensed general contractor. Material pricing reflects current South-region lumber-yard cost; labor reflects Houston-market crew economics.