In case anyone was wondering, or for future reference in case anyone
in the future is *stupid* enough to install a drywall ceiling, my
building inspector in New Jersey said that 1/2" sheetrock for the main
ceiling is fine. They only require 5/8" for the firestopping between
the stud wall and foundation since a fire can spread very quickly
behind the wall since the studs provide fuel, and go all the way up to
the joists.