What is the residential code for ceiling drywall thickness in Ontario(painted surface)
Unless you have a suite in the home, I do not believe the ceiling board is actually for "fire code" but more for rigidity and being able to span the distance between ceiling joists. So 5/8 for 24 " joist spacing and 1/2 fireguard ( once again, not for the fire rating but for rigidity) for 16" on center. I would never recommend regular drywall for any ceiling application, especially if the ceilings are being sprayed.
If there is a residential suite involved, then there are more regulations
Not sure if that is the actual code, but that is recommended in my circles, and what I would do in my own home.
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