Permitted Exceptions. Height limitations stipulated elsewhere in this chapter shall not apply to church spires, belfries, cupolas and domes, monuments, chimneys, flagpoles, fire towers, water towers or masts and aerials or to necessary mechanical appurtenances or to parapet walls, except that no parapet wall may extend more than four (4') feet above the limiting height of the building, or to farm silos, provided that the silo is located no less than one hundred (100') feet from any lot line.