Penthouses or roof structures for the housing of stairways, tanks, ventilating fans, air-conditioning equipment or similar equipment required to operate and maintain the building and fire or parapet walls, skylights, spires, cupolas, steeples, flagpoles, chimneys, water tanks, silos or similar structures may be erected above the height limits prescribed by this chapter but in no case more than 25% more than the maximum height permitted in the district, except that spires, steeples, silos, water towers and radio and television towers shall have no height restrictions except where stipulated by the Federal Aviation Agency.