Insulating a metal shop?

Right now that's the plan for the ceiling but it could change. I might leave the ceiling uncovered in case I need to add extra insulation. I'd like to test it out this summer and see how it feels. As long as it's not miserable then I should be alright.

I'd prefer to lay the sheets horizontally but I think the corners will look better if I hang them vertically.

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That looks like it'll work nice. The air space seems like a good idea too. How are you attaching the foam and spacers?