The height limitations of this chapter shall not apply to silos, belfries, cupolas and domes not used for human occupancy, nor chimneys, ventilators, skylights, water tanks, communications towers, similar necessary mechanical appurtenances usually carried above the roof level. Such features, however, shall be erected only to such height as necessary to accomplish the purpose they are intended to serve. The provisions of this chapter shall not apply to prevent the erection above the building height limit of a parapet, wall or cornice for ornament (and without windows) extending above such limit not more than five feet. Public and quasi-public buildings and other similar permitted uses shall increase the required front, rear and side yards by one foot for each foot by which such building exceeds the height limit herein established for such zone in which it is located, and further provided that in no case shall any building have a height greater than 35 feet overall unless it is specifically permitted by the Schedule of District Regulations.