To the best of my knowledge, there is no code that requires a stud wall to be covered with drywall, unless it is serving as a fire barrier. The openings in the wall in this picture are between the existing 16" oc studs - no extra framing was required. We just cut the wall material out between the existing studs, added a nailer at the top and bottom, then wrapped the resulting opening with drywall. My advice would be to check with your local building inspector about your specific application.