(1) Except in dwelling units and except as provided in Sentence (2), the surface flame-spread rating of wall and ceiling surfaces in corridors and walkways, exclusive of doors, shall not exceed 25 over not less than 90 per cent of the exposed surface area and not more than 150 over the remaining surface area.
(2) Except within dwelling units, corridors that provide access to exit from sleeping rooms and that have a fire-resistance rating of not less than 45 min shall have a flame-spread rating conforming to the appropriate requirements in Subsection 9.10.17.