Located on 23rd Street in Manhattan’s West Chelsea District, HL 23 sits next to and under the High Line historic railway district, which bisects the site. Completed in 2010, this project contains 14 floors and 42,000 square feet of ultra-luxury residential space with generous ceiling heights and expansive column-free zones, as well as 3,585 square feet of street level gallery space and an elevated terrace/garden area.
The HL 23 project is a testament to the versatility and beauty of steel and showcases the ability of the Owner, Architect, Structural Engineer, and Contractors to work together for inventive solutions in a unique site.
Innovative Aspects of the Project
The site is 40-by-49 feet at the ground floor. The floor plate of the building, which is smaller at the base than at the top, owes its uniqueness to the existing elevated exposed Highline Railway, which was retrofitted into a city park facility. The primary steel structure is clad with a mega-panel glass and stainless steel curtain wall system. The glass mega panel system is located on the North, South and part of the East facades, with the remainder of the East façade clad with an all stainless steel system.
HL 23’s distinct reverse-tapering shape comes from the dramatic sloping of the South and East facades, creating a dynamic and undulating three-dimensional composition. The building slopes East from bottom to top, creating a large, destabilizing cantilever over the high line. The building’s dual-lateral support system is the most intriguing element of the structure. A sleek Steel Plate Shear Wall System (SPSW) is located at the elevator and stairs in combination with a full-building, perimeter-braced frame system. As a true sign of synergy between form and function, the architect incorporated the perimeter lateral pipe braces into the final interior aesthetic of the residences.
Architectural requirements played a large part in the final structural layout. The use of structural steel was driven by three primary factors – minimizing the overall weight of the structure for the capacity of the raft foundation, minimizing the amount of interior columns, and providing the perimeter diagonal architectural expression. With the choice of steel, the SPSW system provided the project with the benefits of increased stiffness and smaller dimension – both tremendous advantages for this site.
In New York City, most residential buildings are designed using a cast-in-place reinforced concrete flat plate system to maximize floor-to-floor height. However, due to the unique geometry of the building, the sprawling architectural layouts, the quality of the soil, and the hybrid gravity and lateral load system on the perimeter of the building, steel was the more economical and the efficient material of choice. Floor beams are composite with the concrete slab-on-deck; however, many of the intermediate steel beams were removed to increase headroom in the living areas.
2013 Ideas2 – National Recognition; 2012 ACEC National – National Award; 2012 ACEC New York – Diamond Award; 2012 AIA – Merit Award; 2011 NCSEA – Outstanding Project; 2011 SEAoNY – Finalist
Alf Naman Development, Developer; Neil M. Denari Architects, Architect; Marc Rosenbaum Architects, Collaborating Architect; Stephen V. DeSimone, Principal In Charge; Ahmed M. Osman, Project Manager; T.G. Nickel & Associates, Builder