Phil L wrote:

400mm? do you mean between screws?

IMV this may be fine for wallboards, but ceilings will sag if not fixed
every 150 - 200mm

Well your joist spacing will limit the screw frequency in one direction,
and there seems little point in going that much denser in the other
direction...

Perhaps it depends a bit on if you are using 9 or 12mm board, I usually
use 12mm and have never noticed any sag at all in the space of 400mm
(i.e 32 screws per 8x4' board).

--
Cheers,

John.

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