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This in-depth comparison covers every dimension of choosing between plywood and OSB for roof sheathing: installed cost (OSB is 10-15% cheaper), strength under load (similar), moisture behavior (plywood dries faster, OSB swells at edges), nail-holding (plywood slightly better), weight (plywood is lighter per sheet), and code approval (both APA-rated). Includes recommendations by climate zone and project type, plus links to our Plywood Calculator and OSB vs Plywood for Roof page.
For roof sheathing, OSB and plywood are equivalent under code at the same span rating. The differences that matter in practice are what happens when they get wet, what they cost, and how long the deck will sit exposed before it is dried in.
| OSB | Plywood | |
|---|---|---|
| Cost per sheet | Lower | Higher |
| Weight | Heavier at the same thickness | Lighter |
| Span rating | Equivalent at the same stamp | Equivalent at the same stamp |
| Edge swelling when wet | Swells, does not fully recover | Swells, mostly recovers |
| Drying | Slow | Faster |
| Internal voids | None — very consistent | Occasional |
| Nail holding after a soaking | Weakens noticeably | Holds better |
If the roof goes on and gets dried in the same day, OSB and save the money. If the deck will sit open, if the climate is wet, or if the roof is over a cathedral ceiling where a leak would go unnoticed, pay for plywood. Either way, install it properly — a well-laid OSB deck outlasts a badly laid plywood one comfortably.
They are equivalent under code at the same span rating. Plywood dries faster and recovers better after getting wet; OSB is cheaper and very consistent. Read the stamp, not the material name.
7/16 inch OSB or 1/2 inch plywood at 16-inch rafter centres, and 19/32 or 5/8 inch at 24-inch centres. Heavy tile or snow load calls for 5/8 regardless.
It absorbs water at the cut edge and does not fully recover. Most of the swelling seen in the field comes from sheets butted tight with no expansion gap rather than from the material itself.
Yes, provided both carry the right span rating and the thicknesses match so the deck stays flat. That is common when replacing individual bad sheets on an older deck.