These stories contain terracotta veneers that harmonize with the marble facade below it and the mansard roof above. At the center of the Central Park South facade, the five center bays at the twelfth and thirteenth stories (floors 11 and 12) contain an arcade composed of arches with paired pilasters. On the Grand Army Plaza side, there are horizontal band courses above the thirteenth story. The 58th Street facade is a scaled-down version of the two primary elevations on Central Park South and Grand Army Plaza. A marble balcony runs above the thirteenth story on all sides. The top floors are within a green-tile mansard roof with copper trim. The Grand Army Plaza side contains a gable, while the 58th Street and Central Park South sides have dormer windows on the sixteenth through nineteenth stories, corresponding to interior floors 15 through 18. The turrets on the northeastern and southeastern corners are topped by domed roofs. The twentieth story (floor 19) is the top story of the mansard roof; above it is a twenty-first-story penthouse, labeled as floor 20. Mechanical features The hotel originally contained three sets of pneumatic tube mail systems: one for guest mail, another for guests to order food from the kitchen, and a third for the hotel's various operating departments. The hotel also originally had 10 passenger elevators, 13 dumbwaiters, and three sidewalk elevators. These elevators included four at the Central Park South lobby, three at the 58th Street lobby, and two near Central Park South, for long-term residents. The hotel's water storage tanks had a capacity of , and the hotel could filter of water from the New York City water supply system each day. The mechanical plant in the subbasement originally contained nine boilers; a coal plant with a capacity of ; fourteen ventilating fans; and an electric generating plant with a capacity of . Also in the subbasement was a refrigerating plant that could make of ice every 24 hours, as well as a switchboard made of Tennessee marble, which controlled the hotel's power and lighting. Interior The hotel has a steel frame superstructure with hollow tile floors, as well as wired-glass enclosures around all stairways and elevators. Originally, five marble staircases led from the ground floor to all of the other floors. As constructed, the stories above the ground floor surrounded a large courtyard, which was covered over with office space in a