My apartment ceiling remodel has ground to a halt. The contractor
discovered that there are no wood studs above my horsehair plaster and
steel lathe ceiling (circa 1895), only metal and concrete. (The
building was originally a hotel.) He thought (eronneously) that he'd
be able to screw 5/8" drywall directly to the plaster and that it
would hold. The city inspector thought otherwise, and advised that we
hire and architect to design framing to support the drywall.

BUT, I was wondering, can 1/4" or 3/8" drywall (because of its much
lighter weight) be scewed directly into the horsehair paster and steel
lathe ceiling without falling down, if it is not screwed into any
studs? I've done a test by screwing a drywall screw into the plaster
(which is about an inch thick), and it holds very well. It's only
when you rock it from side to side with a good amount of force, using
the extractor-side of a hammer, that the plaster starts to crumble and
the screw falls out.

So, which do you think would be the better/cheaper/safer option,
framing and then attaching 5/8" drywall to the frame, or somehow
fastening thinner drywall directly to the plaster ceiling?

Thanks very much.