I have a two-car attached garage. The floor is cement, of course. That cement is connected to a large cement driveway.
There are two standard windows in the garage and an insulated door leading to the house.
The garage is below one of my children's rooms. That room has always been a bit of a challenge to keep cool, perhaps because it's above the hot garage.
My garage gets crazy hot in our Georgia summers. Main door open, door closed - it doesn't seem to make much difference.
Also - it remain very hot at night. In fact, it might cool to 80 degrees at night outside - and at 11:30PM when I go from the garage to outside, it feels cool outside.
I wonder if the driveway heating up transfers heat to the cement driveway floor through the evening.
In any event, is there an easy solution? I haven't tried opening the windows because we don't have screens yet. I also thought about installing some sort of powered vent with thermostat to the outside.
Or, perhaps a simple ceiling fan would help. I'd like to keep electric costs down.
What you need to do, is insulate the ceiling/upstairs floor, then seal. Best thing in your situation, is to use Spray Foam, 1) to seal from any CO from leaking into the upstairs, and 2) to create a airtight seal. Also, is there a cold air return in that room, have you had a HVAC tech come and check temps, air flow, etc.?
How old is the house, and was the room original to the house, or an after thought?