I was asked to quote repacing a ceiling in a 12' x 13' room. The existng ceiling is I belive 1/2" thick and sagging. Can 5/8" be placed over this without long term problems? Or should the existing be removed, new vapior barrier and replace existing insulation put back? I know 2-3" long screws would be needed and I would need to be sure to hit the rafters.I am not looking forward to all the insulation coming down on my head.