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I have a 20×25 detached metal garage that I'm turning into a climate controlled workshop. I'm installing a 36K BTU mini-split A/C. I live in North Central Florida so I will be cooling 9-10 months of the year. I'm gutting this building down to the studs, adding some wiring and then insulating and running drywall 8' high.

My question is this- since I'm going to be running the A/C full time most months do I need to install a vapor barrier? And if so, what would be the best combination of vapor barrier and insulation.

I'm considering sprayfoam in the ceiling(underside of roof) since theres not alot of wiring up there and it's not getting sheathed but then using fiberglass Batts in the walls.

Also, what happens to spray foam if there's a roof look. Will there be a mold infection that I just can't see?

Any and all advice is welcome. Thank you.
 

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I have a 30 x 70 metal building outside of Tucson. I have seen condensation down the inside of my building. I have decided that I am going to spray 4" of closed cell foam over the exterior walls and roof.
This does two things stiffens up the panels and removes the area where moisture will attach to the steel. Fiberglass is crap when it gets wet. Rockwool/mineral wool will not be as bad but the water still has to go some where. Then there are the undulations of the metal panels with either of the other insulation's perfect place for condensation.
I have looked at a lot of insulation for steel buildings and have decided like the foam that they use for steel to steel connections it is crap. I used 1/8" thick glastic for my metal to metal connections. The inspector asked me what was the insulation value of the glastic, I said zero. It is not insulation it is there to be a thermal break. He asked me what the rating of the glastic was
I told him it is 340C. Which should be good enough for an Arizona summer.

The pic is where the water heater location. There is red steel Z beam and you can see the glastic on the exterior of the red iron. Also installed at the floor. With the hat channel the walls will be 8.5 inches thick. Take that electric company
 

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