Nelson Byrd Woltz gets super technical at Hudson Yards.

By Alex Ulam

Until recently, you wouldn’t have wanted to go strolling at any time of the day near Hudson Yards, the two gigantic superblocks located on the far West Side of Midtown Manhattan. There was little street life there and almost no nature. Barbed-wire fences and concrete walls lined the streets and concealed the large, sooty pits packed with commuter and Amtrak trains. Indeed, everything about the place was man-made, even the hilly landscape surrounding the train yards below. Walking around was disorienting because the walls cut off view corridors and limited access to Midtown Manhattan and the adjacent Hudson River Park.

Now this formerly desolate expanse is being transformed by a $25 billion private real estate development, which the Related Companies, the project’s developer, is touting as the largest private build-out in the United States and the biggest in New York City since Rockefeller Center. In place of two gaping holes in the city’s fabric, there will be a 28-acre neighborhood with offices, apartments, and more than 100 stores and restaurants. In a sense, this development, where a projected 125,000 people will live and work, is being created from scratch. Decks made of concrete and steel suspended over the rail yards are providing platforms for much of the 18 million square feet of commercial and residential space that is being built.

Construction is already well under way on the Eastern Yard, slated for completion in 2018. One looming, shimmering glass tower already is complete, and others are under construction, including 30 Hudson Yards, an office building that will be the second tallest in the city. The buildings are being individually designed by leading architecture firms such as Kohn Pedersen Fox Associates (KPF), Diller Scofidio + Renfro, and the Rockwell Group. This seemingly no-expense-spared development is intended to wow, and it features iconic architecture such as a curved Art Wall designed by James Carpenter Design Associates. There also is an enormous retractable performance structure known as the Shed, which expands out into the plaza on rollers to provide an indoor venue for performances. Tying the disparate grouping together and softening the impact of the vertiginous skyline is five acres of plazas and gardens being designed by Nelson Byrd Woltz Landscape Architects (NBW).

The multilevel landscape designed for the Eastern Yard includes garden terraces, a streetside plaza with a forest of birch trees for one of the entrances to the High Line, and a plaza at the site of a new subway station for the 7 train, which the city paid more than $2 billion to build. The main event is the elevated plaza known as the Public Square, which rests atop the platform that covers the trains. Plans call for 1,650 plantings and 200 mature trees and include wind- and shade-resistant species such as large-canopied black tupelo trees. The signature elements will include a 200-foot-long S-curved fountain sculpted to create a natural current like that of a river. Entwined elliptical bands of granite will counterpoint the hard-angled shapes of the buildings and provide continuity to a landscape that transitions from perennial beds to a more wooded area north of the site. At the center of the crisscrossing ellipses, there will be a $150 million undulating sculpture called Vessel by the London-based designer Thomas Heatherwick. This 600-ton spectacle, which looks wrought by M. C. Escher, consists of a series of staircases 15 stories high.

Public open space is a key selling point for the Hudson Yards. At the public review process in 2007 that preceded the award of the contract for the site to the Related Companies, the five different developers bidding all highlighted elaborate plans by prominent landscape architects in which the public space was emphasized more than the buildings. To comply with city zoning, the current plan calls for about 40 percent of the site to be public space open to the sky and 15 percent to be enclosed space.

But figuring out how to move from glossy concept plans to building an actual landscape atop a platform, which at its center is suspended 30 to 34 feet above the train tracks, has been a surgical undertaking. What makes this site especially distinctive is that the platforms and most of the buildings at the site are in a sense one structure supported by 300 caissons drilled into bedrock between the railroad tracks below. In fact, only one of the buildings rests completely on actual terra firma.

Since winning the contract to develop the site, executives at Related repeatedly changed their minds about what type of landscape design they wanted and which landscape architecture firm they wanted to design it. In fact, Related went through West 8 and Michael Van Valkenburgh Associates before deciding to host an invited competition in 2012, in which NBW, OLIN, and Sasaki were invited to participate.

“Originally, our model was Bryant Park,” says Michael Samuelian, a vice president of the Related Companies, referring to the famous midtown park in back of the main branch of the New York Public Library. But he says that NBW’s design for Citygarden in St. Louis ended up being an inspiration for the Public Square at the Eastern Yard. “We had thought that we were creating a green landscape in the middle of these towers, and what it has turned into is much more European,” he says, noting that aside from Citygarden, “we have actually had a hard time finding precedents in the U.S. for really good urban plazas. [Hudson Yards] can be a precedent for creating a great urban landscape that is not dependent upon grass.”

One reason for the changes was that it soon became apparent that it would not be technically feasible for the platform to support a green, parklike landscape without compromising the connections to the adjacent number 7 train and the High Line. “The platform required so much stuff, and if it were to have become too much of a landscape, we would have had to build up the platform so much higher than it is now,” says Marianne Kwok, a director at KPF, which designed several buildings at the site. “What we really wanted was permeability, and it also seems like, on the Eastern Yard, having something that was parklike was not appropriate.”

Another example of how drastically plans changed along the way is that key elements from NBW’s winning competition entry were scrapped. “We were constructing a landscape where no landscape exists, so one would assume that it is devoid of culture, history, or ecology,” Thomas Woltz, FASLA, a principal of NBW, told me during a visit to his Manhattan office. Woltz, who was wearing a tie and a fitted, white button-down shirt on a boiling August day, had a genteel calm about him that might come from the time he spends at his firm’s other office in Charlottesville, Virginia. As we spoke about his experiences with the project, it became apparent that his patience and intellectual curiosity were key to his success. “A site that didn’t even exist is still a place of history, culture, and ecology,” he told me. “So the basis of our design was one that revealed and honored these stories.”

To better understand the site’s history, Woltz had included on his design team the urban historian Jill Jonnes, the author of Conquering Gotham, A Gilded Age Epic: The Construction of Penn Station and Its Tunnels, and he delved into archives about the  history of the yards. Woltz says that one of the primary inspirations for the original design was the building of the tunnel from the yards to New Jersey underneath the Hudson River for the Pennsylvania Railroad in the 19th century. At the time, the tunnel was considered on par with other engineering achievements such as the Suez Canal and the Transcontinental Railroad. There is no evidence of that approach in the current plans. “Here the design doesn’t really relate to the history,” Woltz says. “It is sort of heartbreaking for me, because it got us so far.”

However, although the design of the Eastern Yard does not take its cues directly from the tunnel, it honors the memory of the engineering marvel. The plaza at the Eastern Yard may be one of the most complex and high-tech works of landscape ever designed in New York City. To stitch the site into the surrounding street grid, the slab underneath had to be graded and some of the streets elevated. Patrick Cullina, the horticulture consultant for the project, and previously vice president of horticulture and park operations for the High Line, says that the shade, shallow soil, and wind conditions at the Eastern Yard make it one of the most challenging sites that he has ever worked on. “You got the sense that nothing on Earth lives in those conditions,” he says. “With these constructed landscapes, you are looking at tolerances—what plants can adapt to these nontraditional positions.”

Because of the special challenges the site presented, Woltz told the Related Companies that it was imperative that his firm be involved at an earlier stage in the development process and in a more comprehensive way than is typical for landscape architects. He says his design staff members also had to educate themselves about areas outside their immediate expertise, such as engineering, thermodynamics, and physics. “When we started the project, a lot of people said, ‘We won’t need to see you for two or three years,’” he says. “But this was rarely charted territory for landscape architects, and as we began the construction documentation phase, it became evident that we needed to have a coordination role.”

Being involved at an early stage also allowed the designers to prioritize the landscape elements and the pedestrian experience throughout the site. Along with the planting beds and the pathways, NBW was responsible for doglegs of West 31st and West 32nd Streets, which will defy Manhattan’s street grid by curving into the plaza and site from 11th Avenue and emptying out onto West 33rd Street. Because the development is private, it also doesn’t have to abide by city transportation regulations that require curbs, gutters, and standard street widths. Thus, the designers were free to establish a different type of relationship between cars and pedestrians, similar to that of the Piazza del Campidoglio in Rome, by putting the streets at grade with pedestrian pathways that run through the site and demarcating their boundaries with bollards instead of curbs.

Unlike the insular tower-in-the-park model of times past, the Public Square also takes into account its surroundings by establishing connections with the other new, high-profile parks on the city’s West Side: the High Line to its south, and Hudson River Boulevard and Park, under construction directly to the north. When it is complete, the plaza at the Eastern Yard will serve as the hub of a walkable green corridor that extends from the base of the High Line in the Meatpacking District up through Hudson Yards to Hudson Boulevard and ending at West 42nd Street. “Civilians are not going to know the difference between Hudson Boulevard and this park,” Related’s Samuelian declares. “It is going to be one landscape experience.”

There was no textbook strategy for designing the type of landscape that the Related Companies and NBW ultimately decided to build at Hudson Yards. Along with the engineering challenges, the development team had goals to build one of the most sustainable landscapes in New York City. The landscape on the plaza will be fertilized with food-service organic waste from the buildings in the development that will be processed with grinders, dehydrators, and bioreactors. The roofs and plazas also are designed to catch every drop of rainwater that falls on them. The rainwater will be stored in a 60,000-gallon cistern within the slab and used for mechanical operations and to irrigate the plant beds. And although the design does feature raised planters in places, most of the trees and plantings will be placed at grade in large beds of sand-based structural soil to ensure longevity. In contrast to a typical New York City street tree, which has fewer than 100 square feet of soil, each large-canopied tree here will have on average 1,500 square feet of soil. And instead of a series of retaining walls, the design provides large columns with substantial voids that allow soil communication between different planting levels so that root growth will not be impeded.

Many of the aboveground landscape design decisions called for tinkering inside the slab. One of the biggest challenges was finding a way to lower the slab’s temperature so that the city’s increasingly frequent heat waves would not kill off the plant life that in many places is literally embedded within the platform. A ventilation system consisting of 15 large fans comparable in size to jet engines is embedded in the platform to remove the heat generated by covering over the trains and also to provide fresh air to the tracks below. But the ventilation system is not enough to cool the platform and the landscape that rests on top of it. Tests show that the top of the slab can reach temperatures of 105 degrees Fahrenheit during a heat wave, and heat generated by the trains below can cause the bottom of the slab to reach 150 degrees. Because of these unusual conditions, the plant roots above the slab would be in danger of baking.

To ensure plant survival, NBW teamed up with Pine & Swallow Environmental Services and developed what in effect is an air-conditioning system for the roots. The relatively novel approach required threading the planted areas with tubes of cooled glycol, a viscous liquid that holds temperature and cools plant beds. Robert Pine, FASLA, the director of environmental planning and engineering at Pine & Swallow, says although the glycol system uses a lot of energy, there was no alternative. “It is a unique situation, largely because of the scale of the heat coming up below and in terms of the actual temperature of the slab,” he says. “As an environmentalist, I care about not wasting energy, but I tried every other technique, and in the end, there was no other system than a cooling system.”

However, it was a challenge to persuade the Related Companies that the glycol system was essential for the success of the plants. “Related, at first, was like, ‘We are not paying for soil cooling. This is ridiculous [that] you cannot find plants that can adapt to this,’” says Mark Strieter, a senior associate at NBW and one of the project managers. “So we went through a rigorous process modeling it, and finally it came down to proving it to the executives through physics, and you cannot argue with physics. The executives, they got that. They understood it.”

Available structural soils such as Silva Cell and CU Soil also didn’t address the conditions at Hudson Yards, so the designers needed to custom design their own planting medium to accommodate large trees that would have no more than four feet of soil depth and plants that would have no more than 18 inches. One example is a sand-based soil for the large root zones underneath the paving. The issue that obviated the use of available products was the weight of the paving over soil. “If you used regular structural soil, you would have to compact it to such a degree that you wouldn’t get root penetration,” says Pine, who adds that the sand-based structural soil solved that problem with its ability both to support the weight of the paving and to allow roots to expand.

The landscape architects had to find space for their fancy glycol cooling system in the slab along with the various building systems such as high-voltage electric lines, drainage, sewage pipes, and the enormous cistern for stormwater. As the design advanced, it became apparent that costly changes in the design of the slab were going to be necessary to accommodate the landscape design and to bridge the changes in grade necessary to connect to the streets that border the site and to the High Line. These costly changes involved switching the design in places from a plate girder system to a standard steel framing and from precast concrete to set-in-place concrete and metal deck to allow more flexibility in adjusting the platform’s thickness. “Generally, it would just be plate girders, but that doesn’t allow for the grading,” says Robin Fitzgerald-Green, an associate principal at KPF. Changing the slab’s structure, Fitzgerald-Green adds, “allows us to compress the structural sandwich to a level that we could have the finished grades necessary for paving and planting.”

Perhaps the most striking thing about the design process at the Eastern Yard was the flexibility on the part of the various players. Close collaboration among the many designers, rather than just technical knowledge, was crucial to the project’s success. Early in the design process, there was a forum in which all of the architects working at Eastern Yard met with NBW to discuss the project. “During this conversation, we all decided that Thomas had the hardest job, and that he was kind of the glue that brought this all together,” says Kwok of KPF. “It was so critical for him that the landscape negotiated all these pieces.”

Diplomacy was critical, too, in dealing with the engineers who worked on the project. “Nobody prevented us from being at the meetings,” Woltz says, “but it was just clarifying that landscape architecture had to be involved in all the decisions in order to make it successful.” Currently, in addition to construction management on the Eastern Yard, NBW is working on the master plan for the Western Yard. Woltz says that being involved at an even earlier stage in the process with the Western Yard should save on unexpected cost overruns.

To Related’s Samuelian, one of the key successes of the landscape at the Eastern Yard lies in what it conceals. “It is not like digging a hole and planting a tree. It is so much more complex than that,” he says. “And this is just one aspect of that—the waterproofing, the stormwater, the soil cooling, the engineering, all of the utilities running in here—there is a phenomenal amount of infrastructure that supports this landscape, but nobody will know that it is there.”

Alex Ulam is a freelance journalist who writes frequently about urban design and landscape architecture.