According to Ron :
Our 2-car attached garage (my woodworking shop) of our 20-year old home
must not have any insulation above. Either that or the taping job on
the drywall joints must be substandard. Perhaps both.
"Stuff" in now falling on my tools.
The ceiling is trowel textured so it's about 1/8"+ thick everywhere.
Whereever there's a joint, and I mean every(!) ceiling joint in the
garage, the taping has detached from the drywall. By grabbing loose
ends of the paper taping, I can peel it off. The texturing that was
applied directly to the drywall stays put. So, by peeling the loose
stuff off, I end up with ~3" wide strips running in both directions
across the ceiling. It's kind of weird looking, because the texturing
creates some relief and the peeled "runways" are flat and sunken.
How should I repair this problem before repainting the ceiling? Must I
retape? I've never done any taping before. Can I just fill the runways
with joint compound? Either way, I know I won't succeed in getting a
seemless blend into the existing texturing. Does taping have a purpose
in addressing expansion, inferring that I should try to retape it?
Thanks for all advice.

Probably adhesive backed paper tape with inadequate mudding, moisture
and freeze-thaw has finally killed the glue. Paper tape very often
comes loose in unheated buildings.

I would suggest first checking to ensure that attic venting etc. are
working properly, and that the drywall isn't deteriorating.

Assuming attic reasonably good (it probably is), use adhesive fiberglass
mesh tape, and put at least one layer of mud over it. The mud will
penetrate thru the tape and anchor it far better than the adhesive alone.

If you don't tape it at all, it'll crack.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.