I'm wondering the same thing. I have a larger taller garage/workshop attached to my smaller, shorter two car garage. It's board and batten siding on the exterior, and so looking from the inside of the two car garage toward the attached shop, the divider wall is exterior siding. I can't figure how to make the interior portion drywall and the exterior stay board and batten. Tried trimming out a section of the wall, but that messes with the footings and other things.