Roof decking replacement cost

Cost per sheet and per square foot

Deck sheathing replacement runs $2 to $8 a square foot installed. A standard 4 × 8 sheet is 32 square feet, so that is $64 to $256 per sheet, cut in, nailed off and re-covered.

The wide band is access and quantity. Two sheets on a walkable gable sit at the bottom; a scattering of single sheets across a steep cut-up roof, each needing its own set-up, sits at the top.

When the deck has to go

Softness underfoot. Delamination — the plies of an OSB or plywood sheet separating, usually along a long-running leak. Visible rot at the eave, which is where ice dams put water. Sagging between rafters, which means the sheet has taken water and lost stiffness. And spacing: old plank decks with gaps wider than the sheathing rules allow need overlay before a new covering goes on.

Pricing an unknown honestly

The convention that works: a percentage contingency in the estimate — five per cent is typical — plus a stated per-sheet rate for anything beyond it, agreed before the crew starts. On a 21-square roof that contingency covers roughly two to five sheets depending on the rate, which handles the ordinary case. Anything larger becomes a conversation with a number already attached to it rather than an argument on the driveway. The estimate template carries both lines.

What replaces it

Match the thickness of what is there — usually 7/16" OSB or 1/2" plywood on 24-inch rafter spacing — and keep the panel gaps the manufacturer asks for so the sheets can move. Nail off to the schedule, not by eye. And put the new sheet in full: cutting a patch to fit a hole leaves unsupported edges that telegraph through the shingles within a season. Once the deck is right, the sequence resumes at underlayment — see the installation guide and the underlayment guide.