On 26/04/2020 11:25, Roland Perry wrote:
I've got an 8ft wide room that I wish to fit with a false ceiling.

2x3" battens (maybe an overkill, but they are easy to source) then
plasterboard.

How far apart should they be spaced?

The existing joists, which I won't be relying upon at all, are 15" apart.
Mr Google has loads of info from Building Regs, here's an example picked
at random:
https://www.fdean.gov.uk/media/3225/...march-2016.pdf
- suggests 400 centres, and that 2x3 is maybe slightly on the skimpy
side for 8ft.