OSB or plywood: which board should I use?
OSB and plywood do many of the same jobs, and both come in grades for different conditions. The right choice depends on where the board is going and what goes on top of it.
How they differ
OSB (oriented strand board) is made from wood strands pressed together with resin. Plywood is made from thin layers of veneer glued with the grain crossing. Plywood usually holds screws better near its edges and copes better with repeated wetting. OSB is usually the cheaper of the two for the same thickness.
Grades to know
- OSB3 is the load-bearing grade for humid conditions, and the one most often used in building
- Plywood is sold for interior or exterior use: for anything that may get wet, use exterior-grade structural plywood
- Tongue-and-groove versions of both are available for floors
Where each is usually used
- Flat roof decks: OSB3 or plywood, depending on what the roof covering manufacturer approves
- Floors: chipboard is the usual floor deck in houses, with OSB3 or plywood as alternatives; plywood is often used as an overlay under tiles or vinyl
- Shed and garden room floors and walls: OSB3 or exterior plywood on a treated timber frame
- Hoarding and site use: OSB is a common, economical choice
What to check before ordering
- The thickness your joist or rafter spacing needs
- Whether the roof or floor covering manufacturer names a particular board
- Square edge or tongue and groove
- Whether the board will be exposed to the weather before it’s covered
This is a general guide, not a specification. Your builder, architect, building control or the manufacturer will confirm exactly what your project needs.
Get it priced
Send your sheet materials list, with sizes and thicknesses, for a quote.
Common questions
Is OSB as strong as plywood?
For many building jobs OSB3 does the same job as plywood of a similar thickness. Plywood usually holds fixings better near the edges and copes better with moisture. Where it matters, follow the specification or the manufacturer’s guidance.
Should I use OSB or plywood for a shed floor?
Both are used. OSB3 is the economical choice; exterior plywood copes better if the floor might get damp. Either way, lay it on a treated frame kept off the ground.