Expansion gaps for OSB flooring?

[JT101]

Hi everyone.

Am installing OSB3 square edge sheets (8' x 4') x 18mm as a subfloor straight onto joists. I am aware you need to leave a 10mm expansion gap around the edges, but I have read a few pages which recommend a 3mm expansion gap between boards.
Not sure I've ever seen this done before. Is it necessary? I gather with plywood sheets, they are cross bonded and so expand and contract less.

Thanks

 

[Notch7]

3mm should be enough, although Ive done jobs and they have been butted tight together with no issues. 10mm sounds like a lot!

The reality is that osb is likely to be in an unheated warehouse at the suppliers and if its going into a centrally heated house, its likely to shrink rather than expand.

If you are going onto joists over a vented void with no insulation below then there is a chance of some expansion I suppose. If its first floor, then likely to be in a very dry environment.