The plastered ceiling in my living room (15'X 15')is sagging around 3-4" in the center. I need to remodel the room, but I need to fix the ceiling first. I am planning on slowly jacking up the existig ceiling (plaster and all) and sistering in new joists. The attic over the room is not finished and has vermiculite insulation blown in between the 2X6 joists. I don't want to remove the plaster because of the mess the insulation dust would create in the house. My question is has anyone done this or anything like it before? Any suggestions are greatly appreciated.