At 4 p.m. on a bright spring day, if you’re positioned along the High Line, you’ll feel the sun’s rays beating down on you. This makes sense—the High Line is an elevated outdoor park exposed to the elements—but sunshine isn’t a guarantee here. The High Line cuts through the heart of New York City’s booming westside development, bookended by high-profile buildings like Renzo Piano’s Whitney Museum of Art and the gleaming towers of Hudson Yards with lots of new construction in between to block the sun from the popular pedestrian walk.
Bound by water on all sides, New York City has always been forced to grow vertically; but this stretch of land along Manhattan’s West Side Highway is becoming a fortress of glass and concrete as developers eye its waterside proximity. At this particular location along the High Line—between 13th and 14th Streets—the park is mostly boxed in by glassy towers. The park’s gardening zone, the Washington Grasslands and Woodland Edge, is filled with light-loving prairie grasses and perennials like little bluestem and coneflower that increasingly don’t see the sun.
“We’re pretty sure that all the plants there would have died if we had done the as-of-right massing,” says Weston Walker, design principal and partner at the architecture firm Studio Gang.
He’s telling me this on a cloudy spring afternoon while standing at the eighth floor windows of the firm’s newly opened office building, 40 Tenth Avenue. In front of us, the High Line snakes past The Standard Hotel and cuts between two tall glass buildings. Like its neighbors, Gang’s 10-story structure is built from steel, glass, and concrete, but as Walker hinted, there’s something noticeably different about it.
Viewed straight-on from the Hudson River, 40 Tenth looks like a simple rectangle. Shift to the right or left, though, and the building cuts inward, creating a dramatic faceted facade. The new development is part of Gang’s exploration into “solar carving,” a marketable term the firm uses to describe its process of shaping buildings based on the sun’s location and its desired effect. Architects have done some form of this for thousands of years, but Gang has advanced the practice by using software to create detailed solar path diagrams that allow the studio to shift, tuck, and slant a building’s massing into an optimized shape.
You can see this with Gang’s other buildings including Solstice on the Park, a 26-story residential tower built last year in Chicago’s Hyde Park neighborhood whose angled windows are oriented to the city’s latitude in order to maximize sunlight in the winter and minimize heat transfer in the summer.
Forty Tenth is similar to Solstice in that the studio used modeling software to analyze a host of parameters including neighboring buildings, plot orientation, and the sun’s path to determine where the building should be “carved” so as much light as possible hits the High Line over the course of a year. In this case, the tower was set back from the elevated park to make space for a second-story outdoor plaza. Both sides of the building slant downward, bowing out at the eighth floor before tapering back inwards toward the bottom of the site. The effect is as if a jagged-toothed giant took a couple nibbles of the facade. According to the firm, the design increases the amount of sunlight to hit the High Line from 351 hours per year for a conventionally designed building to 1,164 hours per year.
Gang’s 40 Tenth is an extravagant bellwether for a tension that’s been rippling across major metropolises: As cities grow, density increases, often in the form of more and taller buildings. Urban density is generally considered a good thing when it comes to sustainability efforts (the more people sharing resources and taking public transit, the better, the thinking goes), but big buildings can also come with trade-offs like shadows and reduced public space.
Architects and city planners have tried to minimize these trade-offs for decades by creating zoning regulations that aim to increase the amount of sunlight that reaches the ground-level of neighborhoods. In 1916, New York City became the first city in the United States to implement a zoning provision that set a limit on how high and how large a building could be. The rule was a reaction to the Equitable Life Building, a 40-story stone skyscraper designed by Edward H. Kendall and Arthur Gilman in 1915 that cast a seven-acre shadow on the surrounding buildings and streets. The provision resulted in the classic “wedding cake” building design that New York is known for, in which the tops of buildings are a series of stepped setbacks that create more open skyspace.
In 1961, the city implemented floor-area-ratio limits that capped the square footage of buildings. Developers who wanted to build taller could create ground-level public plazas, for which in return they were given more space to build upward. Then in 1982, the city took the protection of open sky even further, implementing the first zoning ordinance that limited the amount of sky a building could obscure—in this case 75% of the sky surrounding any new building had to remain open. As a time capsule of a news story from the New York Times explains it, “Compliance can be complicated, but basically a structure succeeds if someone standing 250 feet away can see about three-quarters of an imaginary sphere above and around its top.”
Before the time of advanced parametric modeling, these blanket regulations were some of the most effective ways to advocate for the street level of cities. Today, these rules still exist, but they’re not the only lever architects and city planners pull when it comes to protecting access to the sun.
A couple years ago, the international architecture firm NBBJ came out with a provocative proposal for a “shadowless” skyscraper that used the building’s reflective facade as a way to bounce light onto London’s darkened streets. Renderings depicted a pair of skyscrapers whose tops expanded outward to capture as much sunlight as possible before transferring the light between the buildings and down to the street via optimally positioned angles in the glassy facade.
The rendering garnered attention for its unorthodox problem solving, but the skyscraper was never built. “You don’t necessary have to build these things,” says Tim Johnson, head of NBBJ’s New York and former president of the Council on Tall Buildings and Urban Habitat. “You can prove them in a digital world.” He says the building really wasn’t that crazy of an idea, anyway. After all, buildings have been harnessing light for thousands of years. “It’s not like we just figured this out,” he says. “Think about the Pantheon—the architect essentially made the building capture the sun. Open the doors on the first day of spring, and the sun is blasting you right in the eyes.”
Of course, the world is a different place today than it was during ancient Roman times. The rate at which cities, particularly in developing countries, are growing has prompted the UN World Habitat to declare that we need to be building a city for a million people every week for 30 years if we’re to keep up with population growth. The truth is, cities need to grow—and fast—which has prompted architects to get creative about how they think about designing dense but liveable cities.
Danish architecture firm Henning Larsen recently won a competition to help design the master plan for a district in China’s Shenzhen City, a megatropolis of more than 20 million people. Instead of building roads above ground as it’s traditionally been done, Henning Larsen’s plan calls for a network of underground highways that would allow the development’s street level to become a sprawling plaza designed for pedestrians. Likewise, the mega malls China is known for will be pushed underground into sunken plazas and retail arcades, creating space for open plazas and smaller buildings above ground that will be interspersed with tall skyscrapers.
For cities like New York, where development has already consumed much of the available land, totally reimagining the master plan isn’t realistic. Instead, incremental changes are cropping up, like a new bill that requires new buildings and major renovations to include green roofs, solar panels, or wind turbines. It’s likely that many of these spaces will remain privately accessible to building residents and tenants, but projects like Seattle’s vegetative Amazon Spheres, which are open to the public, show how office buildings can also become an amenity for neighborhoods. Johnson of NBBJ says his firm is actively thinking about how they can design buildings where the first two floors are open to the public as programmable spaces that the community can interact with. Opening the building as a public amenity doesn’t change the fact that the building and the shadow are there, but it does help a city to feel less closed off.
As for 40 Tenth, it’s a glimmering reminder of how buildings, despite their relative permanence, can respect the dynamism of a city. Cities shift, morph, expand, and sometimes even contract. Buildings, by contrast, stand resolutely in place, often for decades at a time. It’s getting easier for architects to ensure that discreet buildings are designed with an eye toward the long-term livability of cities. “With the technology we have now, we’re in a position where we can really make bespoke specific responses to unique site conditions,” Walker says.
But even with the best modeling software, it’s impossible to predict how a city will change. The best architects can do is to peer into a cloudy crystal ball and think about how their buildings can live among a constantly growing, consistently altering landscape.