Finishing off our large attic space and we went with 3" of closed-cell spray foam (hot roof application) on the slanted ceilings.
My concern is heat transfer through the joists. We live in MN and the winters get cold. Some options I've considered for the ceiling:
1) Just drywall. Pros: It's easy and less expensive. Cons: I'm concerned that the heat transfer through the joist will somehow show on the drywall and instead of a nice smooth ceiling, you'll see joist lines.
2) 1/2" of rigid foam (R-3) and then drywall. Pros: Creates a buffer between the visible drywall and the cold joists. Cons: May not be enough R-value to really protect the drywall and ideally rigid foam should go on the exterior side of spray foam. So maybe it's just a waste of money.
3) Drywall and then covered with a layer of shiplap. Pros: I'm not sure this has any pros other than that this is a look that the wife likes and provides another layer of material that might stand up to cold spots better. Cons: I don't really think it's any better than just drywall in terms of heat transfer on the joist.
What's the smart thing to do in this situation?