This residential project involved the combination of two stacked, independent apartments that overlook Central Park on the Upper East Side of New York. The existing structure relies on two-way spanning, pre-war concrete slabs with draped, welded wire fabric bearing on a concrete-encased steel frame. The main structural feature of the space is a signature staircase that joins the two levels and penetrates through a demolished bay in the intermediate floor slab. Imagined by Workshop/APD as a spiral stair, it occupies the center of the removed slab bay.
A unique structural solution evolved from the architect’s design direction when considering the constraints of the site conditions. As the spiral portion of the stair was intended to occupy the center of a structural bay, this meant that the base of the stair would land directly at the midspan of a concrete slab without the capacity to accept such a load. At the upper floor, it also meant that a bridge element was necessary to access the top of the spiral stair.
The structural solution imagined the entire stair and bridge as a combined, cantilevered element, reaching out into the double-height space from the strengthened edge of the existing second-floor structure. CRAFT worked closely with the stair fabricator, Caliper Studio, to design a stair structure that was intentionally short, which hovered above the existing lower slab when installed. Once loaded, the structure then deflected under dead load in a controlled and intentional manner to make contact with the floor below without imparting loads to the slab. Workshop/APD then created a shadow line at the base of the stair to emphasize the nature of the stair floating above the floor.
PROJECT TEAM
Architect: Workshop/APD, Fabricator: Caliper Studio
