mini split, insulation question for garage makeover

[SouthLake]

want to install a mini split system...

here is the set up...
2 car garage with insulated doors, garage is 22 feet deep, 20 feet wide, and has a no ceiling to the roof peak, so to the peak its about 14' high. entire garage is totally unfinished and open to exterior walls and roof.

i want to insulate the walls, and install slat board on the lower 8', easy enough.

my question is regarding this ceiling. i need to keep the ceiling open, as the overhead space is required to accommodate vehicles put up on hydraulic lift.

I would like to simply put up R12 (13?) foam insulation panel boards that are about 2" thick (4x8 i think) they have foil covering on both sides. Attach them to face of the rafters on ceiling up to the roof peak. would this be sufficient?

im afraid if i put this mini split system in and leave the ceiling open, or not insulated enough, im not going to be able to cool off the garage or heat it.

 

[edcantu9]

I have a similar set up garage. I ran baffles from soffit to ridge vent at the peak. Put in r13 fiberglass and then covered it up with foil faced foam board. Works great. This was my first summer with it and it cools down quick when I run the through the wall AC. It would be worth it to do the extra work and put in fiberglass then cover it.

 

[SouthLake]

Just wanted to follow up and say thanks for all the help of this forum.

installed a 18000BTU Mitsubishi mini split in my garage. put R13 paper faced in the walls, closed the walls up, installed circulation vents to the ridge vent and stapled R19 foil faced in the rafters... the mini split can get the garage down to about 70 degrees when its 95 outside im really happy with how well that unit works.

installed a threshold seal on the bottom of the garage door (on the floor) which helped get a tighter gap on the bottom of the garage door. had to close off the attic access as well and install a door.

all self installed (except i had a company do the insulation).

installing the mini split took about 6-7 hours from start to finish. self evacuated it with HF kit and it fired right up. I helped a family member put a 22,000btu one in his 4 car garage and the learning curve took us considerably longer, two days for that one. but doing it a second time at my place things went much faster.