Foam board insulation is easy to use and a great DIY way to add some insulation. It comes in standard-size 4×8 sheets and smaller sizes, in thicknesses from 1/4-in. to two inches.

I realize that R20 is a bit light for a roof in Canada, but I plan to use ice and water shield as a vapour barrier on the warm side of the installation. After all, it’s just a shop.