Eigenvector wrote:
If I have ceiling joists that are 48" apart, will 5/8" drywall sag if
mounted on it?

I'm not seeing too much information about that around, even though I'm
pretty sure 48" is pretty standard framing for a basement.


Maybe you're trying to solve the wrong problem.

Forget the drywall - it's too heavy.

Perhaps ceiling tiles - they're 48" and should be quite easy to install
flush with your joists.