OSB or plywood roof decking: which is better, and what happens at a reroof?

Shingles and Materials · Updated October 13, 2026

Short answer. Either works: APA rated OSB and plywood with the same span rating are built to the same performance standards and are treated as interchangeable for roof sheathing, typically 7/16 inch or thicker over rafters 24 inches apart. They fail differently when they stay wet, with plywood delaminating and OSB swelling at the edges, and at a reroof damaged sheets are replaced as found, so your contract should state a per-sheet price and require photos of what was replaced.

Two ways to make a panel

Plywood is built from thin wood veneers glued in layers with the grain alternating, which gives it strength in both directions. Oriented strand board (OSB) is made from long wood strands laid in cross-oriented layers and pressed with resin into a solid panel. They look nothing alike, but APA, the Engineered Wood Association, says that in the applications they are made for, the two are virtually interchangeable, because both are manufactured to the same performance standards. APA-rated sheathing panels are bonded with water-resistant adhesives such as phenolic resin, not the urea formaldehyde used in some indoor products.

What matters on a roof is the stamp, not the material. Every APA rated panel carries a span rating such as 24/16. The first number is the maximum spacing of roof supports, in inches, the panel is rated to span; the second is the spacing for floors. Panels also carry an exposure rating. Exposure 1 panels can handle construction delays and the underside of a roof deck, but they are not meant for permanent weather exposure. APA warns that "CDX" plywood, a common trade term, is an Exposure 1 product, not an exterior one.

Thickness and spans

Georgia's residential code, the 2024 International Residential Code in effect since January 1, 2026, sets roof sheathing spans in a table shared with subfloors. The common sizes look like this:

Span rating	Minimum thickness	Max roof span with edge support	Without edge support
24/0	3/8 inch	24 inches	20 inches
24/16	7/16 inch	24 inches	24 inches
32/16	15/32 or 1/2 inch	32 inches	28 inches
40/20	19/32 or 5/8 inch	40 inches	32 inches

Edge support usually means small metal H-clips between sheets midway between rafters, though tongue-and-groove edges or blocking also count. Many newer Georgia houses have trusses 24 inches apart with 7/16-inch OSB, often with H-clips, and some clips also set the 1/8-inch gap APA recommends between panels so they can expand without buckling. GAF's instructions call for at least 3/8-inch plywood or OSB under its shingles.

Thickness also matters for nails. The code requires roofing nails to penetrate at least 3/4 inch into the sheathing, or all the way through a thinner deck, so a thin or soft deck holds shingle nails poorly in high wind.

How each fails when it gets wet

Neither panel likes staying wet. GAF's field guide describes what trapped attic moisture does: plywood delaminates and rots, and OSB expands and rots. APA notes that both can show a rough surface, flaking, or swelling at the edges after long moisture exposure, and that its tests show no loss of structural capacity once a panel dries back to normal moisture content. In other words, a panel that got wet during construction and dried is fine. A panel that stays damp from a slow leak or a poorly ventilated attic is not.

On a Georgia roof, the usual culprits are a long-running leak at a pipe boot or flashing, a missing drip edge letting water wick into the deck edge, and attic condensation. Signs include soft or spongy spots underfoot, ridges in the shingles where swollen panel edges telegraph through, dark staining on the underside of the deck, and nails backing out.

During a tear-off, a good crew checks the deck before any underlayment goes down. They walk it, feel for sheets that flex or give underfoot, look for delaminated plies and swollen OSB edges, and check around chimneys, pipes, valleys and the eaves, where water problems concentrate. Isolated bad sheets are cut out and replaced. When damage is widespread, or the old deck is too thin or too gapped to hold nails well, re-sheeting the whole roof can be the more sensible fix, and that should be priced as its own option rather than sheet by sheet.

Older plank decks

Many older Georgia homes have solid board decking, often 1-by-6 or 1-by-8 boards, instead of panels. The code allows asphalt shingles over wood structural panels or solid lumber sheathing. GAF's guidance calls for boards at least nominal 1 inch thick and no more than 6 inches wide, with tight joints of roughly 1/8 to 1/4 inch at most. Wider boards, bigger gaps, knotholes or sagging sections usually mean sheathing over the boards or replacing sections. GAF also cautions that resin in some wood planks can soften self-adhering membranes, which affects how valleys and eaves are detailed.

How deck replacement is priced at a reroof

Nobody can fully judge a deck until the old shingles are off, which is why decking is a common surprise on replacement day. A fair contract handles it in writing:

A per-sheet price for replacement decking, stating the thickness and material, and a per-foot or per-board price for plank repairs.
Whether any sheets are included in the base price.
A requirement to photograph damaged decking before it is covered, so you can see what you are paying for.
New sheets matched to the existing thickness, so the roof plane stays flat.

On an insurance claim, decking that has to be replaced is typically added after tear-off as its own line item, measured by the square foot (a full 4-by-8 sheet is 32 square feet), and submitted to the carrier with photos as a supplement. Whether it is paid depends on the cause and your policy; long-term rot from an old leak is often treated differently from storm damage. Roof Claim Answers explains the process in its article on roof supplements.

One upgrade to consider while the deck is open

If a reroof includes new decking, the Department of Energy's Building America program notes you can choose OSB with a foil radiant barrier on the underside, installed foil side down, which reduces heat radiating into the attic. See our guide to attic heat and shingles before deciding.

Who to call

Decking is where honest documentation matters most. That is a particular strength of Robust Roofing, the top recommendation for Georgia roof replacements and insurance work: its licensed Property and Casualty adjuster documents damaged decking and scopes it into the claim or a supplement with the carrier, and the job's photos, documents and status are available to the homeowner in its RoofMap portal. Read its guide to roof decking rot or its overview of roof insurance claims.

Common questions

Is OSB or plywood better for a roof deck?

Neither is better across the board. APA says panels with the same span rating are virtually interchangeable for roof sheathing. Plywood tends to delaminate if it stays wet and OSB tends to swell at the edges, so keeping the deck dry matters more than the choice.

What thickness should roof decking be?

On rafters or trusses 24 inches apart, the 2024 IRC allows 7/16-inch panels rated 24/16 with or without edge clips, or 3/8-inch panels rated 24/0 with edge support. Many roofers use 7/16 inch or thicker.

Do I need H-clips on roof sheathing?

Only when the span table requires edge support for the panel and rafter spacing you have. They also help keep the recommended 1/8-inch gap between panels.

How is replacement decking priced?

Usually per sheet, stated in the contract before work starts, with plank repairs priced per foot or per board. Prices vary with thickness and material, so get the number in writing.

Does insurance pay for rotted roof decking?

It depends on the cause and the policy. Decking damaged by a covered storm is commonly added through a supplement, while rot from a long-term leak or poor ventilation is often treated as wear and tear.