The stair and elevator shafts of all buildings except private dwellings, hereafter erected more than two stories high, shall be enclosed continuously by incombustible material, consisting of reinforced gunite not less than 2½ inches thick, or of solid portland cement plaster not less than 2½ inches thick on metal lath and metal frame or of reinforced concrete not less than three inches thick, or of any fireproof material or construction that will pass the standard fire test of the Underwriter's Laboratories of a period of at least two hours. The thickness must in all cases be sufficient to give rigidity.
('72 Code, § 151.038) Penalty, see § 10.99