In article , george [dicegeorge]
writes
On 12/11/10 20:43, 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
The book I'm reading says put 3" by 1" battens perpendicular to the joists,
correctly spaced for your boards, and shimmed if there's any unevenness.
I havent tried yet myself,
I wonder what those who have will suggest..
(the book says the hardest thing is taping over the joins)
[g]

The alternative is to cut the boards short to suit the joist pitch.
Using 2400 x 1200 boards you're cutting 120mm off the length of each
board which is an easy task with a stanley knife

I'd recommend using 2400 x 1200 boards as it means fewer joints, your
35sqm with cropped 2280 x 1200 boards comes out at about 13 boards
whereas using 1800 x 900 mm minis comes out at 22 boards or a lot more
joints.

If you want to keep it DIY then use taper edge boards and don't skim. I
view 9mm as little better than cardboard so would use 12.5mm but you
will need help to fit them.

I wouldn't add extra support for the tapered edges (which are running
cross joist) but would leave a 3mm gap, scrim tape and be generous with
the board finish jointing mix to fill the gap and add strength.

The end joints aren't tapered and will be (slightly) noticeable but you
can save the cost of a plasterer if that is important.
--
fred
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