lath and plaster ceiling

I need to overboard a ceiling for plasterboard. The existing ceiling is old lath and plaster and pretty cracked. Do I need to get the old ceiling down first or can I just find the joists and screw the new boards to them over the top? Thanks!

Hello! I had my lath and plaster ceiling taken down a couple of weeks ago. I am planning on plasterboarding soon. I'm wondering if there is anything that I need to do while I have access to the area that is soon to be covered. The electrician has already been in to tidy away the wires and...