Agricultural or industrial structures, such as barns, silos, grain elevators, water storage or cooling tanks, discharge stacks, or similar types of structures generally erected to heights exceeding the maximum limits established in the district regulations for the zones where they may be located, may also exceed the designated height regulations, provided such appurtenances shall be erected only to such height as is necessary to accomplish their intended purpose and, in the case of industrial structures, are set back a distance equal to their height from all property lines.