So it’s currently 100 degrees F in my garage today. I’m sure it will only get worse as the summer goes on. I added some of those insulated garage door panels, but I don’t think they did anything.
Now I’m wondering if I should add fiberglass insulation to the attic space above the garage. Would this help, or just lock in the heat? Would using a radiant barrier up there work better?
Get/borrow a thermal camera, and use that to see where the heat is coming in. Some libraries have thermal cameras, but that might be rare. You can also get very cheap and nasty thermal cameras from Aliexpress for $60 AUD
Good suggestion. Our local Home Depot rents these as well.