Will this work? Insulating a garage ceiling

Just saw the Roxul in Lowes after looking at the website. Why would anyone NOT use that stuff? I hope I can take some of my R19 back and use this stuff. I am certain to use it in the garage when I finish that this fall...

i cannot wait for the energy savings this winter with the pellet stove and 2 wood stoves fully operational, refurbished old addition with R50 ceiling and garage ceiling [LR & Kitchen above] redone...

Any down side to the Roxul?

Got an airloss audit done last ~July. Home was modestly leaky and had 4 main points of air penetration. I finished 3 of them and since then have also had the house re-sided with foam and taped tyvek. I'm guessing the house is now borderline too tight - I'm expecting to have small draft issues with my stove this winter and already considering where I'd want to introduce some fresh cold air from (i.e. crack a window near the stove?)

I really want to consider it, but I'm going to price out batts + 1" of foam insulation over the walls first. I can't see spray foam being done for under $800 (a sales call to provide a quote + someone coming out and doing it over 4 hours or so + materials).

If I'm still doing batts on top of that, we're not talking a whole lot of savings in labor and cost vs. putting batts in myself and then 1" of foam on top of the studs (reducing thermal bridging).

Foam is great but has a very long breakeven period compared to the pink stuff. I could not justify it. I looked into it when I was building my house. Half of the year I am heading with wood and the other half cooling with a heat pump so I had to double my payback due to no utility cost with the heat. The same was the case with the tankless water heater. With only 2 people in my house there was no justification for it.

Foam is great but has a very long breakeven period compared to the pink stuff. I could not justify it. I looked into it when I was building my house. Half of the year I am heading with wood and the other half cooling with a heat pump so I had to double my payback due to no utility cost with the heat. The same was the case with the tankless water heater. With only 2 people in my house there was no justification for it.

Just put a sheet of 1/2" right on top of the existing drywall, then blow in additional cellulose or fiberglass right on top of the existing insulation. No need to tear it down, and foam panels will not save much heat and cost a lot of money.

EDIT: didn't see that a room was above it. Disregard. Tear it down and do it right. You won't regret it. I was thinking this was open attic above the ceiling.

I believe to be bedrooms on top of the garage. Yea a couple of feet of blown in would be Cheap.