For the purpose of this chapter, the term
FIREPROOF CONSTRUCTION means a building in which all parts that carry loads and resist strains, all exterior walls, all interior walls or partitions, all stairways or elevator enclosures are made of incombustible materials, and in which all metallic structural members are protected against the effects of fire by being imbedded in a material which shall be entirely incombustible and a slow conductor of heat. However, if the metal framework of the roof is more than 18 feet above any floor or balcony it may be protected by a suspended ceiling of metal lath and cement plaster not less than one inch thick, and if the metal framework of the roof is not less than 25 feet above any floor or balcony, fireproofing of the members of the roof framework may be omitted.
(‘82 Code, § 15.04.010)