OSB (Oriented Strand Board) is a panel material made from large wood strands that are pressed and bonded in cross-layered directions. The strands are oriented: in the outer layers they run lengthwise, in the inner layer crosswise. This gives the board strength in all directions. OSB is recognisable by its coarse, visible strand pattern.
Types of OSB
| Type | Application | Moisture resistant |
|---|---|---|
| OSB/1 | Interior, decorative | No |
| OSB/2 | Structural, dry | No |
| OSB/3 | Structural, humid | Yes (limited) |
| OSB/4 | Heavy structural, humid | Yes |
OSB/3 is the standard for building projects — suitable for structural use in a humid environment (but not for permanent outdoor use).
Where is OSB used?
- Timber frame construction — As wind bracing (racking board) on the studs
- Roof decking — As a substrate for roof covering
- Floor panel — As a sub-floor on joists
- Formwork — Temporary for concrete pouring
- Wall and ceiling finish — Industrial/rugged look
OSB in timber frame construction
In a timber frame wall, the OSB board sits on the outside of the studs:
1. Studs and rails (the skeleton)
2. OSB board on the outside — gives the wall rigidity (wind bracing)
3. Breathable membrane over the OSB
4. Ventilation cavity
5. External cladding (weatherboard)
On the inside:
1. Insulation between the studs
2. Vapour barrier
3. Plasterboard or cladding
Dimensions
| Board size | Thicknesses (mm) |
|---|---|
| 122 x 244 cm | 9, 12, 15, 18, 22 mm |
| 125 x 250 cm | Same |
Common thicknesses:
- 9 mm — Wind bracing, light applications
- 12 mm — Standard structural
- 18 mm — Floor, roof decking, heavier structural
OSB vs. plywood
| OSB | Plywood | |
|---|---|---|
| Composition | Pressed strands | Cross-layered veneer |
| Appearance | Coarse, industrial | Smooth, more refined |
| Strength | Good | Better |
| Price | Cheaper | More expensive |
| Exposed use | Only for an industrial look | Yes |
| Moisture resistant | OSB/3: limited | WBP grade: good |
Related terms
- Timber frame construction
- Plywood
- Breathable membrane
- Battening