geraldthehamster wrote:
Having installed appropriate joists in the 30 sq m half of my first
floor that didn't have them, I now want to put down a temporary floor
on which I - and the joiner who will build my dormers - can work, to
complete this part of my renovation. I want to lay loft board or
similar, to avoid dirtying and damaging the pitch pine floorboards
that I have stacked in the garage, that will be the finished floor.
Does anyone have an opinion on the cheapest way to create such a
temporary floor, that will be strong enough? The joists span 3.5m to
each side of a dividing wall, and are at 400mm (ish) centres.

Regards
Richard

Put your pine floor down and cover with hardboard.
Tape the joints.

Andy.