This 10,000 square foot triplex penthouse addition on top of the 12 story Clarendon Apartments incorporated an existing 3,000 square foot mansard structure, which used to be the “tapestry gallery” in William Randolph Hearst’s former 5 story apartment. The new structure, which is in the Riverside-West End Historic District, won unanimous approval from the New York City Landmarks Preservation Commission. The mansard has been transformed into the core of a residence for a family and their museum-quality collection of antique “fin-de-siecle” furniture, lighting, vases and paintings, by building a new multilevel addition within and around the mansard structure. The design required a plan of steel transfer girders, extending the building elevator up two floors, adding a residential lift, new mechanical and electrical services and a complete reconstruction of the existing standing seam cooper roof, with new enlarged steel windows. The multi-level plan rotates about a mahogany and brass central stair hall, which is illuminated by a skylight through glass plank floors above.