Roof Deck & Sheathing Replacement in Toronto & the GTA

Nobody budgets for roof decking. It's the layer you can't see from the ground — the plywood or boards your shingles are nailed to — and it only announces itself as a spongy spot underfoot, a sag visible from the street, or the smell of rot in the attic. Most rotten roof deck is discovered mid-reroof, when the old shingles come off and the crew finds what years of slow leaks and attic condensation have been doing quietly.

Sheathing fails for two reasons: water from above through failed shingles or flashings, and moisture from below when a poorly vented attic lets warm indoor air condense on the underside of cold wood all winter — a classic GTA problem that mimics a roof leak. Repair means cutting out the bad sections back to the rafters, replacing with proper exterior-grade plywood, and fixing whichever moisture source caused it, or the new wood rots on the same schedule.

We quote sheathing repair honestly: on most reroofs it's a few sheets, not a whole deck, and our quotes state the per-sheet arrangement up front so mid-job discoveries don't become mid-job surprises. Full roof plywood replacement is reserved for widespread rot or old plank decks too gapped to hold nails. Note that replacing the deck as part of structural changes needs a municipal permit; nailing new sheets over rafters during a reroof normally doesn't.

• Deck inspection across the full roof once old material is off — walked, not eyeballed
• Cutting out rotten, delaminated or mould-affected sheathing back to sound framing
• New exterior-grade plywood or OSB, matched to existing thickness and gapped for expansion
• Overlay sheathing on plank (board) decks too gapped or split to hold modern fasteners
• Renailing of loose but sound existing sheathing
• Rafter-edge checks, with minor sistering of surface-damaged framing where needed
• Diagnosis of the moisture source — leak path or attic ventilation — that caused the rot
• Full integration with the new underlayment and roof covering going on above

• How many sheets need replacing — the difference between a few soft spots and a full redeck
• Plywood thickness and grade required to match your roof
• Plank versus plywood original deck, since board decks often need full overlay
• How accessible the damage is once the roof is open
• Whether rot has reached rafters or trusses, which moves the job toward structural repair
• The ventilation or leak fix needed so replacement wood doesn't meet the same fate
• Lumber market pricing at the time of the job

Every home is different, so we don’t publish flat prices — the quote is free and based on your actual job.