Permitted exceptions. Height limitations stipulated elsewhere in this chapter shall not apply to open amusement uses, church spires, belfries, cupolas and domes, monuments, water towers, chimneys, smokestacks, flagpoles, radio and television towers, masts and aerials; or to parapet walls, except that no parapet wall may extend more than four feet above the limiting height of the building; or to farm buildings or structures on farms, provided that these farm buildings are not less than 40 feet from every lot line.