The height limitations of this chapter shall not apply to chimneys, silos, church spires, gables, cupolas, standpipes, flagpoles, monuments, television and radio antennas or towers, cables, scenery lofts or water tanks and similar structures and necessary mechanical appurtenances for that zone in which the building is located provided that no exceptions, when connected to and a part of a principal building, shall cover at any level more than 10% of the area of the roof on which it is located. All items in excess of the height regulations shall be set back from the property line at least a distance equal to their height.