Exceptions. In Rural, Agricultural Research, Commercial and Industrial Districts, the maximum height requirement shall not apply to the following: barns and silos, belfries, bulkheads, chimneys, church spires, domes, flagpoles, grain elevators, masts and aerials, monuments, observation towers, skylights, smokestacks, utility poles and towers, ventilators, water tanks, windmills and solar collectors, provided:
(1) They are erected only to such height as is necessary to accomplish the purpose they are to serve.
(2) If over 40 feet in height, they shall not exceed a height equal to their setback distance from any property line.
(3) They are not intended for human occupancy as dwellings.