Pinching a skyscraper.People have an innate desire to build higher and higher, and modern skyscrapers seem to scratch that itch pretty well. They capture our imaginations, showcase human ingenuity, and look pretty damn cool to boot. (Exhibit A: The Burj Khalifa in Dubai. The thing is over half a mile tall!)

High-rises make some compelling economic sense, too: They cram a ton of floor space into expensive real estate markets like Tokyo and New York City. Economist Ed Glaeser, in his book The Triumph of Cities, goes so far as to say they’re the saviors of our cities. If you worship at the Church of Density, then skyscrapers are not just your Bible, they’re your ticket to the afterlife.

But while skyscrapers may save your soul, they won’t save the environment. Michael Mehaffy at the New Urban Network has written an extensive paper explaining why.

On a pound-for-pound basis, skyscrapers don’t make a lot of environmental sense. As the floors stack higher, the amount of concrete and steel bound up in the building increases nonlinearly, as does the energy required to make the raw materials and assemble them into final form. High-rises require 60 percent more energy per floor in raw materials than low-rise development, according to one study. And while you’d think the places would be cheaper to heat and cool, owing to shared walls, ceilings, and floors, those gains are often lost due to exposure to the wind and sun. To top it off, most high rises don’t have operable windows, meaning you can’t just crack the window to cool the place off — that air has to be conditioned.

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Ah, you say, but if cities grow up, they’ll stop mowing down farms and forests as they expand endlessly outward. But skyscrapers have done a questionable job of reducing sprawl. In part, that’s because many are office buildings. Office towers do a marvelous job of concentrating brainpower downtown, but they have done little to increase the density of people living in cities. When quittin’ time comes, most office workers go home to a more thinly populated neighborhood. Writes Mehaffy:

Office buildings, of course, don’t do anything by themselves to increase residential density, and depend for many of their benefits on their location and the pattern of commuting. If they are confined to largely single-use office districts whose employees empty out in the evening, decamping to remote residential enclaves, then this is clearly not much of an ecological benefit.

An obvious solution would be to build residential towers next to office towers. But residential high-rises have their own set of problems. High-rises have also been called vertical gated-communities, isolating their wealthy residents from the neighborhoods outside. Many of the more plebeian towers were built in the 1950s and 1960s to house people displaced when neighborhoods were bulldozed to make way for freeways. They were badly neglected and quickly became symbols of urban blight.

There are other reasons why people are loath to live 50 stories above the ground. Many of us prefer to be closer to the action on the street. Families also tend to shy away from tower living, with its limited or non-existent outdoor space.

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Mehaffy advocates for lower-slung, higher-density development like that found in many neighborhoods built at the end of the 19th and beginning of the 20th centuries. He says the “sweet spot” is around 50 people per acre, or about 32,000 people per square mile. (Think Brooklyn or Baltimore.) Beyond that point, he says the beneficial effects of density begin to level off.

It’s not clear where he got that number, but I can say it’s startlingly high: New York City has around 30,000 people per square mile. Can you hit that kind of density without stretching toward the sky? It’s possible: The city of Paris clocks in at about 54,300 people per square mile, and height restrictions have kept the height of most buildings there to five or six stories, tops. Still, New York City and central Paris are expensive places to live — not everyone can afford it. That highlights one of the confounding factors in the quest to densify cities: It drives up the cost of living. High-rises only contribute to the problem because they’re so expensive to build and maintain.

Creating dense, livable cities is a difficult problem, and difficult problems are seldom solved simply. High-rises have been pitched as that easy solution. They’re not.

That’s not to say skyscrapers don’t have a place in cities — they absolutely do, whether they house offices, condos, or shops. But they’re not a silver bullet. I’d hate to see us start stacking floor on top of floor until we’ve lost touch with the world. We’re more creative than that, right?

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