I'm putting in some new sheetrock in a couple of closets and I've been wondering about how to insulate above them properly after completely gutting them and losing all the insulation above them. Would it work to glue 2" foamboards to the top of the drywall and spray foam the edges for a tight airseal? It's not a huge area, but I have the opportunity to insulate it from scratch above those closets. Spray foam seems cost prohibitive. I figured gluing down 2" of foamboard would give me about R10 then I could rake some of my blown insulation (fiberglass) over top of it. Thoughts? Would this trap moisture? Would it work?

I'd just caulk anywhere that might leak air and then put lots of loose cellulose over it.

can you get to the attic above the closets or are you trying to do it from below?

Yeah I can get up there. Was planning to do it from above. Was thinking I would just glue the boards directly between the joists and on top of the drywall. Then with a can of spray foam seal around the edges. I already have tons of boards.