Park Avenue Townhouse, New York by David Hotson

"In order to create ample spaces for family life, creative work, and gatherings of all kinds, this 19th century Queen-Anne brownstone was enlarged to the maximum amount permitted by the underlying zoning and landmark regulations. Two stories were added at the top of the building under a raked roofline that keeps the enlargement hidden behind the existing mansard roof. The cellar was excavated to create a suite of sauna and steam rooms. The five original stories where structurally rebuilt and furnished with enlarged rear windows, exterior terraces, and new plumbing, electrical, heating and central air-conditioning systems.

With such a pronounced vertical organization, the stair provides the focal element in the organization, use, and experience of the house. The new staircase passes from cellar spa to rooftop studio as a continuously transforming sculptural element. As the stair rises through the building, adjusting to the varied ceiling heights of the rebuilt stories, the enclosing walls around it gradually peel away, opening the stair to the surrounding spaces. As it reaches the double-height family room with its vaulted roof rising behind the exterior mansard, the stair completes its transformation to a pure freestanding helix, turning upward to access the new bedroom mezzanine and ascending through a skylit light shaft to the rooftop studio and exterior terrace." [psa-publishers.com]