I'd guess your main concern is keeping cool, right?
There is a foil backed fiberglass batt that might be better in the ceiling and, even on a wall that get's direct sun.
Not sure, but I believe there is an insulating foam board with reflective backing, too.
Does the shop have a gable vent? One at each end would help. We have them in our house and, with a whole house fan blowing into the attic, we get by in sunny AZ without A/C except on the hottest days.
'The true soldier fights not because he hates what is in front of him, but because he loves what is behind him.' G. K. Chesterton
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Last edited by Gene Howe; 07-10-2011 at 03:48 PM.