If you're standing in front of a stack of 12mm OSB and a stack of plywood wondering which one to load onto the van, you're not alone — it's one of the most common questions we get asked. Both are structural sheet materials, both come in similar sizes, and both will do the job on plenty of projects. But they're not interchangeable, and picking the wrong one can cost you money or cause problems down the line.
Here's a straight answer, without the marketing spin.
The short version
- Choose OSB when you want strong, cost-effective sheet material for roofing, flooring, wall sheathing, or hoarding, and appearance doesn't matter.
- Choose plywood when you need a smoother finish, higher moisture resistance, better screw-holding at the edges, or you're doing something structural that needs a specific grade (like marine or WBP-rated work).
Now let's get into why.
What's actually different between them
OSB (Oriented Strand Board) is made from compressed wood strands bonded together with resin, layered so the strands run in alternating directions for strength. It's what most of the trade buys for general structural work because it delivers strong, consistent performance at a lower cost per sheet than plywood.
Plywood is made from thin layers ("plies") of real wood veneer, glued together with the grain of each layer running perpendicular to the next. That construction is what gives plywood its smoother face, better screw-holding at cut edges, and generally more predictable behaviour when it gets wet — particularly with WBP (Weather and Boil Proof) grades.
Head-to-head comparison
| OSB | Plywood | |
|---|---|---|
| Typical cost | Lower per sheet | Higher per sheet |
| Strength (structural) | Very good, consistent | Very good, slightly better edge strength |
| Surface finish | Rougher, visible strand pattern | Smoother, more even |
| Moisture resistance | Good with the right grade (OSB3), but edges can swell if left exposed | Excellent with WBP/marine grades |
| Screw/nail holding at edges | Can be weaker at cut edges | Generally stronger |
| Best for | Roof decking, wall sheathing, sub-flooring, hoarding, general structural use | Flooring in wet areas, furniture-grade work, marine applications, anywhere appearance matters |
When OSB is the right call
OSB3 (the "3" means it's rated for humid conditions, not just dry) is the workhorse of UK construction sheet material. It's what you'll reach for on:
- Roof sarking and decking — strong, consistent, and cost-effective across large areas
- Wall sheathing — bracing timber frame structures
- Sub-flooring — under carpet, laminate, or tile, where the surface won't be seen
- Site hoarding and temporary works — where cost matters more than finish
If you're covering a lot of ground and the material is going to be hidden behind plasterboard, roofing felt, or flooring, OSB almost always makes more financial sense. 12mm OSB is the most commonly specified thickness for general sheathing and flooring — it hits the sweet spot between rigidity and cost for most domestic and light commercial jobs.
When plywood earns its higher price tag
Plywood costs more, but there are jobs where that's exactly the right spend:
- Visible or finished work — worktops, shelving, built-in furniture, anywhere the surface will be seen or painted
- Wet or exposed applications — marine-grade and WBP plywood are built to handle sustained moisture exposure far better than standard OSB
- Structural work needing certified performance — plywood graded to EN636/2S (like our Structural Hardwood WBP Plywood) gives you a documented, consistent structural rating that's often specified on drawings
- Anywhere you're screwing close to a cut edge repeatedly — plywood's cross-laminated construction holds fixings better at edges than OSB does
A quick note on thickness
Both materials are commonly stocked in 9mm through 18mm. As a rough guide:
- 9mm–11mm — light sheathing, hoarding, non-structural cladding
- 12mm–15mm — the most common range for flooring, roofing, and general structural sheathing
- 18mm — heavier structural applications, larger joist spans, or where extra rigidity is needed
If you're unsure which thickness your specific job needs, it's always worth checking span tables or asking a structural engineer before ordering — getting this wrong is a more expensive mistake than the cost difference between OSB and ply.
The bottom line
Neither material is objectively "better" — they're built for different jobs. If you're weighing up cost against a large area of hidden structural work, OSB will save you money without costing you strength. If the job involves moisture, visible finish, or edge-fixing demands, plywood is worth the extra spend.
Still not sure which one your project needs? Give our team a call — we quote both OSB and plywood daily and can point you to the right thickness and grade for your specific job.