Question 1

What is the difference between OSB 2 and OSB 3?

Accepted Answer

OSB 2 is rated for dry conditions only. OSB 3 carries a humid-conditions rating under BS EN 300, making it suitable for roof decks, floor decks, and wall sheathing where some moisture exposure is possible during and after construction. For most UK building projects, OSB 3 is the correct choice.

Question 2

Can OSB 3 be used as a finished floor surface?

Accepted Answer

OSB 3 can serve as a structural sub-floor, but it is not typically left as a finished walking surface in habitable rooms. It is best covered with a suitable floor finish such as carpet, vinyl, or engineered flooring. Where foot traffic is expected during construction, the 18mm thickness offers better load distribution and stiffness.

Question 3

Do I need to treat OSB 3 boards before use?

Accepted Answer

OSB 3 does not require additional treatment for standard structural applications in humid conditions, provided it is incorporated into a complete building system with appropriate weatherproofing above. It should not be left permanently exposed to rain or standing water without a protective covering such as roofing felt, membrane, or cladding.

Property	Detail
Material	Oriented strand board (wood strands bonded with resin)
Grade	OSB 3 - load-bearing use in humid conditions
Standard	EN 13986, BS EN 300
Nominal Size	2440mm x 1220mm
Thickness Options	11mm, 18mm
Use Class	Humid / semi-exposed conditions (protected from permanent wetting)

Specifications

What it's used for

Fitting and handling

FAQ

Orientated Strand Board (OSB)

OSB 3 Sheet 2440mm x 1220mm