Height limitations stipulated elsewhere in this Part 6 shall not apply to the following when attached to the principal structures: chimneys, church spires, belfries, domes, cupolas, flagpoles, monuments, fire towers, cables, or water tanks, elevator housing and similar structures, and no such exception shall cover at any level more than 10% of the area of the roof on which it is located, and further provided that no such structure shall extend more than 40 feet in height above the height of the principal structure, except as may be otherwise specifically provided in this article. All freestanding structures shall be considered as accessory structures and shall meet the height requirements as set forth in the zoning district regulations, except that freestanding lighting structures shall not exceed 16 feet in height in any zone.