I've posted a lot of questions in this newsgroup so I hope I'm not boring
anyone...

Some dry-lining and ceiling questions:

I have fixed vertical battens every 600mm across the face of all the walls
in the shed. I plan to use 12.5mm plasterboard so do I have to fix
horizontal battens (apart from top and bottom)?

Should I fix the ceiling before dry-lining the walls?...

I was planning to nail 12.5mm plasterboard to the ceiling joists. The joists
are 500mm apart. Do I need to put in "cross-pieces" between the joists? I
was palnning to lay lengths of 35mm Celotex between the joists for
insulation. Is this OK?

Thoughts and suggestions please.

Thanks