I have a older addition on my home with loose vermiculite insulation. I want to redo the dry wall including the ceiling as it is cracked and has some water damage and move a fixture. I don't want to pull down th eold dry wall as it is holding up a deluge of insulation. Can you drywall over the existing ceiling and if so what steps are needed. I was thinking of using an adhesive and a layer of 3/8 drywall (to avoid excessive thickness) and then drywall screws throughout. Any help would be appreciated.