The height limitations of this chapter shall not apply to barns, silos, residential chimneys, spires, cupolas, elevator penthouses, domes, flagpoles, birdhouses, flues, monuments, radio towers, television antennae or aerials, water towers, water tanks, transmission towers and cables, smokestacks, air-conditioning units or other similar roof structures and mechanical appurtenances, provided that:
A. No such structure when located on a building roof shall occupy an area greater than 25% of the total roof area.
B. No such structure shall be used for any purpose other than a use incidental to the main use of the building.
C. Any antenna located in a district permitting residences shall be limited to a height that is equal to or less than the distance from the base of the antenna to the closest property line.