The Nomad wrote:
Evening all,

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?

TIA

Have a good week-end

Nick

Firstly, if you've never plated a ceiling before, you aren't going to be
able to get it good enough to just tape the joints, it will need plastering.

15in centres is slightly odd as they are normally 16in, but no, you don't
need any extra support or noggins.

You're better off using 6X3 plasterboards and get the thinner ones as they
are easier to handle, and they need to be fixed pale side down.

They have to be jointed in the centre of a joist on the shortest edge, that
is to say, the edge that is 3ft will be fixed, the long edge won't, and
obviously you will need to cut them so that they land on a joist.

If the joists are thin, you might want to get some 2X1 batten to add a bit
of extra width to the joists that the boards meet on - you won't need it on
all the joists.

Before you start, mark a line on each wall where the joists are, and use
screws rather than nails to affix the boards.

--
Phil L
RSRL Tipster Of The Year 2008