Plaster boards over wooden ceiling

You can board on to wooden ceiling Firstly if the ceiling feels solid with no movement movement. Secondly if you can see where screws are normally there in to joists so you can use that as guild to where joist are placed

You could plasterboard over wooden ceilings, but I would recommend removing it. Most wooden ceilings are tongue and groove and pinned in to place (blind nailing) and more usual the wood is pinned to battening screwed to the joists (the ceiling). So you won’t know where the joists are and I wouldn’t advise screwing 12.5 boards to the wood as if it’s been installed correctly only the pins will be holding it in place and the boards weigh around 25 kg a piece so a strong chance they won’t hold. Safest option is to remove all the wood and break through the ceiling near the walls (a small hole) and locate a joist and do the same along the wall on both sides. Joists are usually around 400 apart and in older properties not always equally spaced though that’s why I locate each joist and then chalk line them. Hope that’s helps.

I’m not sure as to screwing boards , straight on top of wood planking , would be a fire hazard or against building regulations . So I would personally, remove them , insulate between existing joist with rock wool insulation , ( fire proof ) then screw the plasterboard to joist .

Hi you would be fine fixing new boards over the timber ceiling as long as you hit the joist with a decent size screw normally 55m I wouldn’t worry about fire risk as standard plaster board give you 15 minutes fire rate and a two coat skim over gives you a extra 15 minutes fire protection to.