Ceiling sheetrock for basement apartment

Question

My house consists of two units, the main and basement apartment to which the main is not connected indoors.

I was planning to put fiberglass insulation between the joists and use ultra light 1/2" sheetrock but then a friend told me to use 5/8 for fire resistance reasons. Assuming this is not subject to code inspection, would it be acceptable to go with 1/2"? I've seen sagging between joists as a reason but I'm not seriously concerned about that. In addition to being lighter and easier to work with, I prefer 1/2 to allow that 1/8" extra ceiling space, which is scarce.

Answer 1

Yes, 1/2” thick gypsum board can be installed on 16” o.c. Joists for ceilings with batt insulation. (24” o.c. spacing would require 5/8” thick gypsum board without sagging between supports.)

The Code does not require any special fire separation between units, because there are only 2 units. I also doubt a Building Permit is required because it’s not structural, fire code, energy, or exit related, etc. (That’s why we don’t get a Permit for replacing carpet, painting, etc.)