The drywall ceiling in this 60 year old house has had waves since I bought the place 30 years ago. It didn't have AC for the first 30 years so that explains the waves and sags .
Added another 10" of insulation in the attic and now there's cracks forming . Instead of crawling around in the attic and installing backing I'm thinking of screwing OSB to the room side of the existing ceiling to get things flat again then putting new 1/2" rock on that. Any problems with that idea other then additional costs?