A 1931 office and 1965 annex converted into luxury condos, adding floors, retail, and a pool. Engineers used innovative methods to ensure stability and adapt the structure for sustainable modern use.

The transformation of Manhattan’s One Wall Street’s—a 50-story, limestone-clad, 1931 office tower and 30-floor, 1965 steel-framed annex—into luxury condominiums, is feat of engineering innovation, NYC’s largest historic conversion, totaling 1.6 MSF, including a massive vault 72 feet below and an addition of six floors atop the annex and 175,000 SF of retail at its base. The landmarked building’s fluted exterior, with “wedding cake” setbacks, sits on a tight site above a subway station, flanked by landmarked buildings.

Giving this worn beauty a second act meant balancing technical ingenuity with a respect for architectural heritage. We assessed the limits of the structures to support new residential floors and a rooftop pool.

To ensure the additional height and weight didn’t destabilize the structure, particularly after removal of lower floors for retail, we designed a reinforcing stiffening system utilizing innovative materials to control wind sway, meet current codes, and support added mass.

Setting back the six-floor-addition meant new and existing columns didn’t align, so we redistributed loads with a reinforced concrete transfer slab. Sustainable, voided concrete slabs reduced embodied carbon—and the structure’s weight by 40%. Accommodating the pool’s depth, required creating a long-span, steel structure for a column-free space below. A glass retail addition cantilevered over the street level avoided the need to drill into the subway station.

To bring light into the interior, we punched new openings into the masonry, reduced and relocated scores of elevators and stairs, and removed beams for utilities—all requiring highly creative engineering.

“In the face of an daunting array of challenges—adding six floors , a rooftop pool, and new retail space to a landmarked building with a cavernous, dark office interior just above an active subway station—my team of DeSimone engineers embraced from the outset that nothing short of creative, out-of-the-box thinking could assure the integrity of the structure, preserve and restore the historic facades, and reimagine One Wall for modern, luxury living.”
—Mark Plechaty
Managing Principal
DeSimone Consulting Engineering