Room is a bathroom, 7.5 feet by 9 feet. Old lathe and plaster ceiling. Rough, patchy and I'm having a ceiling mounted fan fitted. So I think I'll take the old one down and replace with plasterboard and get someone to skim it. The ceiling joists are at 12 inch centres. The joists go across the short way, across the 7.5 feet width. So the 'bound' edge of the boards go across the joists and the 'cut' ends butt together at a joist, yes? But do I need to fix the bound edges to noggins between the joists? What board thickness does anybody reccomend? Thinking about it if I use 8' x 4' board (but cut down a lot lengthways) this is going to be 4 pieces, but with long cut edges down the edge, against the wall. I'm expecting to tuck those in above the existing wall plaster. Is that enough or do I need noggins to support those? Many thanks. Presumably foil backed in a bathroom.