Outside the fire limits, when any building is to be erected of brick, stone, hollow block or concrete that could under this chapter be constructed of wood, the inspector or other designated official shall allow reasonable modifications of this chapter relating to brick buildings, in consideration of the use of incombustible material instead of wood. Such modifications, however, shall not permit variations from the requirements of Sections 5-25-650, 5-25-830, 5-25-840, 5-25-880, and 5-25-890.