Parapet walls and false mansards shall not extend more than six (6) feet above the height limit. Flagpoles, chimneys, cooling towers, elevator bulkheads, penthouses, finals, gas tanks, grain elevators, stacks, storage towers, radio towers, ornamental towers, monuments, cupolas, domes, spires, standpipes, and necessary mechanical appurtenances may be erected as to height in accordance with existing or hereafter enacted laws affecting the same.