(a) Except as provided in subsection (b) hereof, water-resistant building paper or asphalt saturated felt or other suitable approved water-resistant paper or barrier shall be applied over all exterior wall sheathing. Whenever conditions are such that moisture due to condensation may accumulate within the wall assembly, the water-resistant sheathing paper or barrier shall be vapor-permeable.
(b) Exceptions.
(1) The Commissioner may approve the omission of sheathing paper where the building is not intended for human occupancy, or where the exterior finish is metal, and in other instances where it is not deemed necessary by him or her for the protection of the sheathing or structure.
(2) Sheathing paper shall not be required over sheathing that has been covered or treated in an approved manner to render it water-repellent, provided that the sheathing material is closely fitted and cut ends which expose an absorbent core to moisture are sealed by caulking or covered with water-resistant building paper or asphalt saturated felt.