Insulation

[Ian]

Sooo, I'm gonna type some stuff up and back this thread up with some pictures in the morning.

I have a 2 bay garage with 2 bedrooms and 1.5 baths over it. The space is cold all winter long because it's basically surrounded on 5 sides by cold air.

The full bath has been down to the studs since we bought the house almost 2 years ago and this winter I started sweating in new shower plumbing, insulating, and other core prep for finishing it this spring. The plumber hacked up the primary joist below where the tub used to be and when I was doing some work on the new shower valve, I noticed the floor was pretty noisy. After some additional assessment I could tell the joist was sagging pretty badly and compromising the structural integrity of what is going to be a tiled shower floor.

Fast forward to this weekend, I dropped a portion of the ceiling in the garage to sister a new joist and support the floor. One thing led to another and I found the 8/3 wire the mouse chewed through in 4 different spots and dropped the rest of the ceiling in that garage bay to make sure the wire was good back to the panel. During the process, I found that close to 70% of the insulation had been compromised by mice, meaning a bunch of trips to bulky waste today getting rid of Sheetrock and insulation.

Now I have one bay of the garage completely exposed and and trying to make an intelligent decision on how to re-insulate before putting up new fire rated sheet rock.

Option 1: R38 batts with the vapor barrier facing the conditioned space which essentially replaces what was there with non mouse superhighway stuff.

Option 2: DIY spray foam kit to seal the underside where the floor from above sits on top of the joists, then the appropriate sized (thinking it will be R30 depth) fiberglass batts under that with the sheet rock keeping everything sealed up.

Option 3: Hire someone for $$$ to come in and do it their way.

My questions:

While I have one bay exposed, should I bite the bullet and tear down the other side? I'm assuming the mice made it to that side too.

Should I consider trying to drop the ceiling height by an inch or so using sheets of foam board for some extra R value?

Am I insane?

Is there something else I should remember to do while I have this area exposed down to just the joists? (I'm going to re-route some coax and cat6e cables already)