Height. The height limitations of this chapter shall not apply to church spires, belfries, cupolas, nor to chimneys, ventilators, skylights, television and radio antennas, water tanks, bulkheads, similar features, and necessary mechanical appurtenances usually carried above roof level. Such features, however, shall be erected only to such height as is necessary to accomplish the purpose they are to serve. The provisions of this chapter shall not apply to prevent the erection above the building height limit of a parapet wall (without windows) or cornice for ornament extending above such height limit not more than five feet. Public and quasi-public buildings, schools, churches, and recreational uses where no reasonable opportunity for occupancy by persons at a level above 38 feet exists, provided that such uses shall increase the front, rear, and side setbacks by one foot for each foot by which such building exceeds the height limit herein established for such zone in which it is located.