I should know better than this, but it sure would be easier if I could get away with it.
I have a 24’ X 28’ double car detached garage that I’ve turned into a woodshop. I started out by completely gutting the interior walls. I then stubbed out the wall studs with 2X4’s ripped down the center. This gave me a total of 5 1/4” depth to my walls. I then insulated the walls with 6” insulation. I than took off the old cedar shake roof and put a monier lifetile heavy shake roof on it, which matched the house. As an underlayment I used Grace ‘Ice & water shield’. This product makes my roof completely water proof. The trusses are open (I prefer it that way) and I would like to insulate the rafters, but I am not sure how to go about this. I live in the Pacific NW and it can be humid and wet most of the year. Because my roof is water proof, could I get away with putting 6” unfaced batts up against the underside of the roof without creating a moisture problem. My shop is a hobby shop and I heat it only when I want to. This can be two to three times a week. Would there be enough air flow through the batts to dry any condensation that would appear? I’m temped to try a section to see what happens. Does anybody have expertise in this category?