Roof structures for the housing of elevators, stairways, tanks, ventilating fans or similar equipment required to operate and maintain the building; fire or parapet walls, skylights, towers, steeples, stage lofts, and screens, flagpoles, chimneys, smokestacks, radio and television aerials, wireless masts, water tanks or similar structures shall be permitted to exceed the maximum height set forth for the district in which the structure is located provided:
(a) No such structure shall exceed the height limits of the district in which it is located by more than 15 feet; and
(b) No such structure shall have a total area greater than 25 percent of the roof area of the building.