Every other line on a roofing quote can be measured from the ground. Decking cannot. The sheathing is under the shingles, and nobody — including an honest roofer — knows how much of it is rotten until the tear-off is done and the deck is walking-inspected.
So decking is quoted as a rate, not an amount. Understanding that rate, and the wording around it, is the difference between a fair change order and a bad afternoon.
What it costs
Sheathing on a modern house is 7/16" OSB in 4×8 sheets — 32 sq ft each. Replacement is priced per sheet, and the installed rate carries material, labour, and the fact that a crew has to stop shingling to do it.
| Item | Typical range |
|---|---|
| 7/16" OSB sheet, material only | $25 – 48 |
| 1/2" or 5/8" CDX plywood, material only | $45 – 90 |
| Installed replacement, OSB | $70 – 130 per sheet |
| Installed replacement, plywood | $95 – 170 per sheet |
| Per square foot, installed | $2.20 – 4.00 |
| Plank / board decking, per board | $25 – 60 |
Typical US contractor pricing at the time of writing, not a quote. Plywood costs more than OSB and most contracts specify matching what is already there — mixing thicknesses leaves a step under the shingles.
The per-sheet rate on a change order is normally higher than the per-sheet cost inside a full re-deck, and that is legitimate: a full re-deck is a rhythm, a scattered eight sheets is eight interruptions.
How much you should expect to need
On a roof being torn off for the first time, in a dry climate, with no known leaks: often zero to three sheets. Contractors commonly build two or three sheets into the base price for exactly this reason.
Where it goes badly:
- Around penetrations. Chimney flashing, plumbing boots and skylight curbs are where water has been getting in. Rot clusters there.
- At the eaves. Ice damming backs water up under the shingles and soaks the first few feet of deck. This is why the ice and water shield requirements exist, and why houses built before they were enforced tend to have soft eaves.
- Under valleys. Same reason: concentrated water, old flashing.
- Under a second layer. A roof shingled over once already has had a warm, damp sandwich sitting on it. See tear-off vs roofing over.
A whole-deck replacement — 20 to 40 sheets — happens on houses with long-standing leaks, on old plank decking too gapped for modern shingle nailing, or when the existing sheathing is thinner than code allows for the new fastener schedule.
The contract wording that matters
This is the part worth reading twice. Look for three things:
1. An included allowance. "Includes replacement of up to 3 sheets" is good. It tells you the rate applies only past that point.
2. A stated unit rate. "$95 per 4×8 sheet, installed" is good. "Decking replaced at cost plus 20%" is workable. "Decking replacement billed as required" is not — that is a blank cheque.
3. Proof of what was replaced. Ask for photographs of the bad sheets in place, before they come off. Any crew will do this if asked at signing; asking afterwards is a different conversation. It costs them thirty seconds and it removes the entire category of dispute.
If two quotes are close and one has a decking allowance and a stated rate while the other does not, they are not the same quote.
Whether it changes the decision
For a typical job, decking lands at 2–8% of the total. Three sheets on a 21-square roof at $95 is $285 against a $12,000 job — real money, not a decision changer.
The case where it is a decision changer is a full re-deck: 30 sheets at $110 is $3,300, which can move a re-roof close to the point where the repair or replace arithmetic looks different, or where a longer-life material starts to make sense because you are paying for the deck work only once.
The short version
Budget $70–130 per sheet installed, expect zero to three sheets on a sound roof, and make sure the contract names both an included allowance and a unit rate before you sign. The rate is rarely the problem. The absence of a rate is.