Hi All
I'm planning to board up the loft properly this winter - putting down 4x2s
at right-angles to the current joists and filling in between with a new
layer of insulation (Celotex/Kingspan or the normal roll insulation stuff),
then boarding over the result.

I'm unimpressed with the T&G chipboard panels the sheds sell for this
purpose and was thinking of using OSB, probably cut into eg. 4ft x 2ft
panels for easy of fitting.

Any thoughts on the right thickness of OSB to use? 18mm seems a whisker OTT,
but I don't think I would trust 11mm. I guess I'm thinking of around 400mm
'joist' spacing.

Thanks
J^n