Towers, spires, chimneys, machinery, penthouses, scenery lots, cupolas, water tanks, radio aerials, television antennas and similar architectural and utility structures and necessary mechanical appurtenances may be built and used to a height not more than 25 feet above the height limit established for the district in which the structures are located; provided, however, that no such architectural or utility structure in excess of the allowable building height shall be used for sleeping or eating quarters or for commercial advertising purposes.