No building shall be erected, converted, enlarged, reconstructed or structurally altered to exceed the height limit hereinafter established for the district in which the building is located, except that penthouse or roof structures for the housing of elevators, stairways, tanks, ventilating fans or similar equipment required to operate and maintain the building, and 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 may be erected above the height limits herein. Such structure shall not have a total area greater than 25% of the roof area of the building, nor shall such structure be used for any residential purpose other than a use incidental to the main use of the building. Radio, television and wireless aerials or masts for individual residential or commercial site use may not be erected higher than 50 feet or 20 feet above the roof line for safety purposes without Planning Commission approval. All antenna, towers or other similar structures for commercial purposes must comply with §§ 154.495 through 154.506 as applicable. Nothing in this section or in this chapter shall be interpreted to permit the erection of any structure in violation of any applicable provisions of any airport zoning regulations.