HL23 by Neil M. Denari: Geometry at its best
The HL23 building, designed by architect Neil Denari, founder of the NMDA firm, is a 14-storey, luxury residential tower and one of the most outstanding examples of contemporary residential architecture in New York.
Located at 515–517 West 23rd Street in the Chelsea neighborhood, the project faced a series of challenges throughout its development.
The challenge
Alf Naman contacted Denari to present a challenging project: an extremely narrow lot that was also partially obstructed by the elevated structure of the High Line.
Denari said that the project took seven years to complete: “We have been doing studies for galleries underneath the High Line for the client Alf Naman. In March 2025, he said: ‘I have a site, you won’t believe it, is a real challenge. Would you liike to take on the project?’ We went through and essentially start the design project that ultimately took seven years to complete”.
Photo By Neil Denari (AI-reconstructed screenshot)
The immediate proximity to these former train tracks, converted into a famous linear public park, required a very specific architectural solution to make the project commercially viable without encroaching on the public space.
“What we had to do for a year, was to convince city planning that the architects weren't egregious, the developer wasn't greedy and that a project of this type needed to be eccentric and restive and problematic rather than conforming”, says Denari.
How high, how wide, what would it be to approach the project?
The conceptual approach
Denari, along with Joseph Chiarelli, partner and operations manager at TG Nickel and Associates, considered themselves very fortunate to have the opportunity to create a building adjacent to a park.
“We were going to do a building on a park that wasn't Central Park or another classic park (...) instead of it being a square, it was a line, so doing a park as a line and a building on a line was really powerful to us”.
In addition, they envisioned that it could become a popular New York landmark, given its prime location, where people passing by the park would see the building every day: “what we also knew and could predict was that was the popularity and the power of this site; but we were going to have a built-in audience every day: everybody was going to come and see our building whether they knew it or not.”
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45% of the sellable floorplate is beyond the zoning for the left side
Photo By Neil Denari (AI-reconstructed screenshot)
3D model and pre-assembly
Using 3D modelling programs to pre-visualise the building during the planning stage was crucial to minimising potential errors during construction, which was carried out in two pre-assembly phases.
“We were able to look with the architect, engineering, and designers at what conflicts we were going to see going up the building before we actually came upon that problem in the field, and it worked flawlessly,” says Joseph Chiarelli.
Photo By Neil Denari (AI-reconstructed screenshot)
About the assembly stage, Denari explained that the first seven floors have concrete poured into the decks every other floor, and cured for 21 days. The lower part of the building was going to be as close as possible to where the steel was supposed to be: “It was like building two separate buildings, the first seven stories and then the last seven because the concrete in the deck finalizes the structure.”
The wall panels were procured from China, because at the time, there was no company in the United States that would take on such a challenging project, according to Chiarelli.
“So not only do we get the benefit of prefabrication, we get the benefit of very thin profile joints, and all of the steel from the frame is wrapped in bead blasted stainless steel, so it's quite an elegant piece”.
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Photo By Neil Denari
Structural innovation
To maximise usable space while adhering to Manhattan’s strict zoning regulations, the team opted for a design featuring gradual widening.
The building's profile, its inclination towards the park, the distinctive features of its facades, and the way the structure is repeated with ceramic cladding all contribute to making it a work that explores the interaction between two-dimensionality and the facade.
From a few blocks away, the building can be seen from the front, but as people pass by, it rotates and becomes a dynamic, three-dimensional structure with a multitude of optical effects.
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Photo By Neil Denari
As the 14-story building rises, its structure expands eastward, creating a pronounced cantilever that leans over the airspace of the High Line itself.
“The luck of the site and the way in which the building essentially is experienced and interfaced at this particular level, 25 feet in the air, where you know if you're walking on the street, you're typically seeing storefronts and signage and so forth, and here you see pure geometry and pure materiality, really, I think at its best.”
Sustainable certification
In addition to its small footprint, High Line 23 incorporates a variety of sustainable building technologies, such as water-saving fixtures and energy-efficient appliances. This has enabled it to acquire LEED Silver certification.
Also, the structure incorporates reused and recycled materials: 75% of construction waste was reused and recycled.
Photo By Neil Denari
Its high-performance building envelope and highly reflective roofing material decrease heat and energy loads and moderate the urban heat island effect.
In terms of its design as a pathway connecting different parts of the city, including HL23, Denari described the architectural evolution of The High Line as a diorama, with important buildings raised alongside it, such as Solar Carve by Studio Gang, Lantern House by Heatherwick Studio or 520 West 28th (known as the Zaha Hadid Building) By Zaha Hadid Architects.
“Because you are moving along, these buildings become kinda like dioramas in a natural history museum.”
Photo By Neil Denari
Sources Front Global, Neil Denari Architect, Consigli, Dezeen
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