I would like to insulate the ceiling in a room with a flat concrete roof.
The obvious first choice is does the insulation go on top of the existing roof or under the current ceiling.
The current roof is asphalt BUR construction. One roofing contractor suggested adding 2" of hard foam insulation on top of the existing roof and then covering it with a new asphalt BUR.
The second option is to add insulation inside. Since the ceiling is nearly 10' high, this is realistic.
What has been suggested is to glue up the same 2" foam board, and then have plaster put directly on the ceiling. Will this really stick?? Do I need to use some sort of lathing? Do I need a special type of foam board so that the plaster will stick?
Finally, I could put up the insulation, studs and a drywall ceiling, however I think that this will turn out to be far more expensive than the other options
Any exeriences with these kinds of jobs?