Replace Plywood Roof Cost Calculator

Full deck replacement runs [RATE:plywood_roof_decking] installed as an estimate. Divide roof area by 32 to get sheet count, then add 10 percent for waste.

Replace only rotted panels unless roughly 30 percent of the deck is gone. Choose plywood over OSB in humid and coastal climates. Get the per-sheet add-on price in the contract before tear-off, and get photos of the bare deck before underlayment covers the nailing.

The most expensive minute of a reroof is the phone call from the roof. Do not authorize a sheet count over the phone without photos of each panel.

Ask them to hold, get the count, and check it against the calculator. A crew that won't send photos or won't wait ten minutes is telling you something.

Laying new panels or new shingles over failed decking is a code violation and it voids the shingle manufacturer warranty. It also hides the rot so the next owner finds it.

If a contractor proposes it as a way to save money, that's the end of the conversation.

Roof decking, also called sheathing, is the layer of 4x8 panels nailed across your rafters. Shingles and underlayment sit on top of it. Nobody can see it until the shingles come off.

That's why decking is a change order, not a line item. Your roofer quotes the tear-off and the shingles, then calls you from the roof once the deck is exposed. Rot comes from leaks around flashing, ice dams, and poor attic ventilation that traps moisture against the underside of the panels.

Signs you can check before the job: sagging between rafters, dark stains on the attic side of the sheathing, daylight through seams, and soft spots that flex when someone walks the roof. If your attic shows none of those, a claim that the whole deck is bad deserves photos.

Sheets are 4 feet by 8 feet, so each one covers 32 square feet. Divide your roof area by 32 and add 10 percent for cuts and waste.

A 1,200 square foot ranch roof works out to roughly 47 sheets. A 1,600 to 2,000 square foot two story lands near 60 to 75 sheets. A 2,400 to 3,000 square foot house with a hip roof needs 90 to 110, because hips generate more angled cuts and more waste than a simple gable.

Roof area is larger than floor area. A 6/12 pitch adds about 12 percent over the footprint. Steeper pitches add more, and they also slow labor down.

Replace only what's bad. That's the default, and it's what most jobs need.

The working rule among roofers is the 30 percent threshold: once roughly a third of the panels are compromised, patching stops making sense and full replacement is the cheaper path. Below that, spot replacement is fine and holds up. The difference between 12 sheets and a full deck at $3.5–$6 on a 2,000 square foot roof is thousands of dollars, so this is the single biggest number on the page.

Watch for the contractor who quotes partial and then converts to full after tear-off. Get the per-sheet add-on price in the signed contract before anyone touches the roof.

OSB is cheaper per sheet at retail. Plywood costs more. Both meet code, and both are used on new construction every day.

The split is moisture. OSB is compressed strands and wax; when the cut edges get wet, they swell and never fully return. Plywood is cross laminated veneers that dry closer to flat. On a roof that stays dry, OSB lasts fine. On a roof that leaks once, OSB edges telegraph through the shingles as ridges.

If you're on the Gulf Coast, in the Pacific Northwest, or in coastal New England, pay the plywood premium. Dry interior climates with good attic ventilation are where OSB earns its price gap. A material swap without telling you is a red flag either way.

The IRC sets 1/2 inch as the practical minimum for rafters at 24 inches on center. Most roofers install 5/8 inch under heavier architectural shingles or tile, and it costs a little more per sheet.

Nailing matters more than thickness. IRC Table R803.2.3 calls for 8d nails at 6 inches on center along panel edges and 12 inches in the field. Under nailed sheathing is the failure point in high wind, and you can't inspect it after the shingles go on.

Get photos of the bare deck with fasteners visible before underlayment. That's your only window.

The decking rate covers panels, fasteners, and the labor to set them. It does not cover everything else that lands in the same invoice.

Underlayment has to be replaced with the sheathing. Old underlayment laid back over new panels leaves a leak path from day one. Drip edge, ice and water shield at the eaves, dumpster and haul away, and the permit all stack on top.

Rafter rot is the one that hurts. If the sheathing rotted, the rafter tops under it may have too. Sistering a rafter is separate labor and separate lumber, and it's priced per rafter, not per sheet.

This is the moment the money moves. The shingles are off, the crew is standing there, and you're being asked to approve an add-on on the spot.

Ask for one photo of every panel they're calling bad, with something in frame for position. Ask them to count out loud with you. Then multiply: sheet count times 32 square feet times $3.5–$6 gives you the installed range. If their number is well above that, ask what's in it.

You're allowed to say "replace these, leave the rest, and stop." You are not obligated to approve a deck you were never shown.

Three things in writing, every time. A per-sheet add-on price. A statement that decking is billed on actual count, not estimated. A requirement that you approve any count above some number, say 10 sheets, before work continues.

Payment schedule is the other tell. Standard is 10 to 20 percent up front, a draw at material delivery, and the balance at completion. A demand for 50 percent before anyone shows up is worth walking away from.

Verify the license and the certificate of insurance directly with the insurer, not from the PDF they emailed you.

Replacing a few sheets on a low slope garage or shed roof is a real weekend job. Panels, a circular saw, a nail gun, and a helper. The math is simple and the fall risk is manageable.

A two story with a 8/12 pitch is not that job. You need staging, fall protection, and the ability to get the roof dried in before weather. A deck left open overnight in rain costs more than the labor you saved.

Split the difference where you can: buy your own panels, have the crew install them, and pay labor only. Confirm your contractor allows owner supplied material first, since many don't warranty it.

May through August is peak. Crews are booked out weeks and pricing sits above the annual average. December through February is when quotes soften and scheduling opens up, in most of the country.

None of that applies if water is coming in. An active leak spreads rot into rafters and insulation, and the seasonal savings disappear inside a month of damage. Tarp it and book the work.