SUMMARY:  Should I air-seal a plywood ceiling, or install a vapor retarder, or is there a way to do both?

DETAILS:  I have a bedroom with no finished ceiling (exposed ceiling joists).

I’m planning to install 3/8″ ply-bead (beadboard plywood) because I dislike finishing ceiling drywall, and ply looks nicer.  The ply appears to satisfy building code for fire concerns.

GBA has drilled into my head how important air-sealing is, so where the edges of the boards meet, I planned to install 1x4s over the seams (top side of the ply, in the attic, between the joists), and caulk the 1x4s to the ply.

However, the installation instructions say, “Exterior Walls and Ceilings separating attics from living spaces should be insulated and have a vapor retarder between the panel back and inner face of the studs, furring or solid backing.”

If I install felt paper between the ply and the joists then I can’t very well caulk the ply seams.  I guess I could install the felt paper everywhere except the ply seams, if that would be acceptable.(?)

FWIW, CZ-2, about 12″ of loose-fill cellulose on the attic floor.

What say the experts?