On 22 May, 14:49, Donwill wrote:
I've started fixing bearers at 24" centres using up my stock of 50mm
celotex in-between.
What is the cheapest material to use for covering the celotex, I thought
of using 12mm plywood but is there a cheaper alternative that is rigid
enough to take lightly loaded screws for small narrow shelves etc. What
about flooring grade chipboard or similar. Any ideas?

Don

12mm OSB is best as it is so saturated with epoxy that it will act as
the damp proof membrane (ack. to Bob Minchin for that piece of
knowledge ! :~)). It is also strong enough to take things screwed to
it. Plus of course it is cheap ~£9 a sheet even in the sheds.
Rob