Except as regulated by Part 20, Airport Zoning Regulations, of this Chapter, the maximum height limitation of this Chapter shall not apply to church spires, cupolas, monuments, silos, domes, or any other structure not intended for human occupancy nor to chimneys, ventilators, skylights, water tanks, or other necessary mechanical appurtenances normally built above the roof level. Such building appurtenances, however, shall be erected only to such height as is necessary to accomplish the purposes they are to serve. Neither shall the maximum height limitations apply to architectural elements (including but not limited to parapet walls, cornices, entrance and building accents), provided that the architectural element is set back an additional foot from all building setback lines for each foot above 35 feet up to a maximum height of 55 feet, and the horizontal width of all architectural elements above 35 feet is no greater than 20% of the linear frontage of the building for each individual tenant.