I would have to add that I had a large chunk of ceiling fall in my
house several years ago and have never been complacent about
ceilings since. Problem we had was a CeilHeat ceiling which was
installed with 3/8 wallboard above and troweled plaster below.
Because the ceiling joists weren’t level the lower layer, which was
full of heavy sand, was troweled on thick to level the ceiling.
Years later more insulation was added, and when the dew got heavy
in the insulation …fortunately no one was underneath …
broke an antique chair.
There are lots of ways for ceilings to get unstable. Another
thing to think about, especailly if you have lots of glass cases