Any portion of the roof structure above that which is used in measuring the height of a building as defined in subsection 22-2.2 as well as penthouses or roof structures for the housing of elevators, stairways, tanks, ventilating fans, air conditioning equipment, or similar equipment required to operate and maintain the building and fire or parapet walls, skylights, towers, spires, cupolas, steeples, flagpoles, chimneys, smokestacks, monuments, watertanks, 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 spires, steeples, silos, water towers, and radio and television towers shall not exceed 50 feet in height above the ground level. In addition all structures are subject to regulations of the Federal Aviation Agency.