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Source and full text on The Atlantic (it is an interesting read overall)Why Can't We Build Skinny Skyscrapers Everywhere?
Within the next few years, the number of New York City skyscrapers that are 1,000 feet or taller is going to soar. Today, there are seven towers in the 1,000-feet-plus club. If construction proceeds as planned on projects now under way or scheduled to break ground this year, that figure will more than double.
In Manhattan, architects are building highest and fastest in Midtown. There, the supertalls aren't just tall—some of them are superskinny, too. In most cases, each unit is basically its own penthouse suite, occupying an entire floor of its building.
Taken on their own terms, the superskinnies represent a feat of architectural design. The new developments going up on West 57th Street may, in fact, be approaching the outer limits of the tall-to-thin aspect ratio for a structure. Just not for the reasons you might think.
"Structurally, there are a lot of very unique challenges, especially for a building that wants a high degree of special views," says Vishaan Chakrabarti, a partner at SHoP Architects and the director of the Center for Urban Real Estate at Columbia University
With an aspect ratio of 1:23—that's the ratio of the longest dimension of the building to the narrowest—111 W. 57th St. is a true needle.
This new kind of skyscraper is popping up all over Midtown—but so far, only there. There are reasons that superskinnies haven't shown up in Chicago, Los Angeles, San Francisco, Dallas, or other cities. Nor are they likely to get much skinnier in Manhattan.
"From an engineering standpoint, there’s a ways to go," Gill says when I ask him how tall and thin the firm can build. "From an economic standpoint, we’re close to the limit."
there are some places where superskinnies will just never go. "For areas that are seismic, the slenderer buildings are not advisable," Gill says.
"It stops making sense in terms of elevatoring," Chakrabarti says. For a project like 111 West 57th St., where each floor constitutes a single huge apartment, this means that elevators chew up floorplate as you rise. And since the entire tower yields only about 300,000 square feet of residential space, there isn't a lot of square footage to lose.
You could go taller with these skinny towers, but it would require something that no U.S. city has in spades: abundant land downtown available for development. The higher you go, Gill says, "the land area you require increases. Doubles. Triples." At a kilometer high, Kingdom Tower's footprint is still manageable. But at a mile high, the base that a building requires becomes much, much larger.
"You end up carving that stuff up [the base area]," he says. "There’s an economics to it that suggests that at this time, and this place, this is what we can do."
Even in Billionaires Row—where Midtown zoning allows skyscrapers to soar—the oxygen has mostly been used up. To build the towers that are rising now, in many cases, developers purchased air rights from adjacent shorter buildings.
In other words, these superskinnies are unique—a "registration of the market," as Chakrabarti calls them. "It is a typology that’s happening, no question," he says, noting that SHoP has at least two more supertalls coming to New York. "But if I look at our overall portfolio, [superskinny, supertall] is not an enormous percentage in terms of square footage."