The room is an extension, single story with a flat roof (yes I know!) approx size is 6.6m * 5.3m (with a corner cut out) the joists run across the short edge (there is a RSJ from the corner of the cut out to the short wall to which the joists 'join'). There was no insulation at all hence it was so hot/cold, I've almost put that right.
The question si as the joists are 15" centres - not a divisor of standard board sizes, which way to run the boards and should I/ do I need to nog the joins/edges of the boards?
My feeling is I need to put quite a bit of wood in there to support board ends/edges to prevent sagging.
As a follow up question 9.5 or 12.5mm board?
Have a good week-end