I have a large roof (100 square) that I put R6 Zip sheathing on. I unfortunately had to first put an entire layer of OSB down first so the zip insulation wouldn’t compress on the rafters. So I have 2 decks, and not sure if that is a good or bad thing?

Now I have to figure out how to insulate the roof. Of course there has been 15 price increases in the last 6 months on everything under the sun, including foam. The cost for closed cell is real high. I originally wanted to do the entire roof with 7 inches of closed cell for R49 plus the exterior R6 zip for a nice R55. However, its way too expensive to hit the whole roof with that much closed cell. I am thinking about doing 2″ of closed cell for a nice vapor barrier and adding some rigidity. Then filling the remaining 8″ of the rafter with open cell? I am so confused. Some people say just put all open cell. The whole “never knowing when a leak surfaces” with the closed cell is a non issue for me. 

I went nuts elsewhere in the home with closed cell. I put 2″ under the slab, and also put 2″ under garage slab. 

The more I read about insulation I get more confused. I have mineral wool in my mind that I cant shake, but I like the idea of all spray foam because its seems like it gets in the nooks and crannies better. I am aiming for an extraordinary score on the blower door test.