Insulation and air sealing on attic side of bonus room
I live in southeastern NC in zone 3. I have a bonus room above my garage. The room does not have typical knee-walls. The pitch of the A-frame was raised to pull most of it out of the room. What I have now is a bonus room that is essentially a normal room with a nearly 8′ ceiling. when the house was built, batts were installed in the stud cavities of the bonus room but were not enclosed on the attic side. So I have batts that are open to the attic with no air barrier of any kind. My understanding is that this is not ideal and the batts should be enclosed on all six sides. My first question is would it be okay to use thermo-ply to sheath or enclose all of the walls on the attic side and seal the seams with foam or tape to air seal? Are there any concerns about trapping moisture if I do this? What is the correct way to go about this?