Manhattan is seeing a building boom, and supertalls, or skyscrapers over 1,000 feet tall, seem to be the new Starbucks. And they have just as many critics, with many decrying the new supertalls for their design, the long shadows they will cast, and their status as conspicuous signs of excessive wealth. No one person is behind the development rush, but Kenneth Lewis would be a good place to start. As managing partner at architecture firm Skidmore, Owings & Merrill, Lewis was the senior designer on the Time Warner Center's 750-foot-tall twin towers and project manager on the Western Hemisphere's tallest building, One World Trade Center. Lewis talked to City & State about some of the things architects have to consider when building super tall. - JC

Airplanes
Airplanes

The primary force dictating supertalls' heights isn't gravity, it's the FAA. Lewis said the agency has placed a 2,000-foot cap on buildings in Manhattan due to its proximity to nearby airports. That means any New Yorker who wants to reclaim the "world's tallest building" title and top Burj Khalifa's 2,722 feet will need to do some serious Washington lobbying. Lewis said preliminary plans had One World Trade reaching the 2,000-foot limit before the master plan settled on its current 1,776.

Wind
Wind

"Once you get above 1,000 feet, wind becomes the critical factor for structure," Lewis said. One reason why: "It makes the building bend. When it bends, it has to come back." He said the human body is more sensitive to this movement when it is lying down, so office buildings and residential buildings are made with subtle differences in structure, with offices "tending to be a little looser, a little more movement to them that's allowable than a residential building."

Money
Money

"These buildings start to lose their efficiencies after about 1,200 feet," Lewis said. Beyond that height, the amount of area in the floor plan that must be devoted to structure or mechanical operations, like elevator shafts, increases compared with the usable area. But just because they are inefficient does not mean they are losing money. "Views are driving value," Lewis said. "The higher you are in a building, the more money you can ask for it."

Geology
Geology

There's a persistent myth that the buildings are taller in Midtown and lower Manhattan because the bedrock there is stronger, or more accessible than in areas in between, like the Village. "It has nothing to do with that!" Lewis said. The clusters were determined by society, not geology, he said, with access to trade and markets driving development near Wall Street and access to the train lines driving it in Midtown. Lewis said Manhattan's bedrock is pretty much available at 20 feet below grade in Manhattan. Builders then drive about 10 to 15 feet into the rock to stabilize their construction.

Prestige
Prestige

With the three tallest completed buildings in the world in Asia, and Dubai having twice the number of supertalls than New York, some long for the days when the Empire State Building was the undisputed champion. But as Lewis sees it, Chinese society is urbanizing quickly – "massive cities need iconic buildings," and New York is no exception. But that doesn't mean the city's skyscraper era is over. "We're about to see another round of this over the next 10 years with the upzoning of Midtown East and the upzoning of Hudson Yards and Midtown West projects and the World Trade Center being completed in 2020. I just see this as the beginning of the next cycle."