Reuters

The average height of towers is climbing — but how high is too high?

If skyscrapers followed a human course of development, we might say they're about to enter puberty. By 2020 the world's 20 tallest towers will achieve an average height of 1,962 feet (nearly 600 meters). That's more than 500 feet taller than their average height in 2010, and more than 700 feet taller than the average in 2000 — or about the difference of the entire height of the Met Life building in New York, which was the world's tallest when it was completed in 1909. Earlier this month the Council on Tall Buildings and Urban Habitat released a diagram of the what the world's tallest buildings will be come 2020:

The image underscores the global race to the clouds. By 2020, according to the council's accompanying report, nine buildings will eclipse (or nearly break) the "megatall" barrier of roughly 2,000 feet (or 600 meters) — twice the height of the Eiffel Tower. As a point of comparison with today's skyscrapers, consider that the Petronas Towers, which were the tallest in the world when completed in 1998, will rank just 27th when 2020 arrives. In the words of the council's report, "600 m seems to be the new 300 m." Likewise, 300 meters (or 984 feet) seems to be the new snowman: by 2020 an estimated 198 towers will reach that height, compared to just 15 in 1995.

All but one of the towers on the top 20 list will be built in the Middle East or Asia. The lone representative from the Western hemisphere will be One World Trade Center, which will scrape sky at a patriotic 1,776 feet (or a less patriotic 541 meters) with its radio antenna. (Which, by the way, why are skyscrapers allowed to include antennas in their height? If reaching my hand upward counted in my height I'd be playing center for the Knicks.) China leads the list with ten of the towers in seven different cities — the tallest being the Ping An Finance Center, in Shenzhen, at 2,165 feet (660 meters).

The tallest tower in the works is the Kingdom Tower in Jeddah, a city on the western coast of Saudi Arabia. The tower will soar to 3,280 feet (over 1,000 meters), making it more than 500 feet taller than the world's current champion, the Burj Khalifa in Dubai. Built at a cost of $1.2 billion, the completed Kingdom Tower will be a mixed-use facility that includes a luxury hotel, luxury condominiums, and office space, in addition to the world's highest observatory. It will also boast "one of the world's most sophisticated elevator systems," according Adrian Smith and Gordon Gill, the project's lead architect [PDF] — with observatory elevators reaching speeds of 10 meters per second, or over 22 miles per hour.

There's certainly a whose-is-bigger element to the recent height craze, but at some point cities must recognize that a tall building stops generating density and starts creating problems of its own. As a building's height increases, it requires more energy to construct and maintain. With that additional height also comes a drop in space efficiency, with structural support occupying area that might otherwise go toward tenants. Earlier this year the financial analyst Vikram Mansharamani even wondered if China's lust for skyscrapers represents unnecessary spending and, by extension, belies a real estate bubble. In its review of the 20 tallest towers, the Council on Tall Buildings argues that the question is no longer how high can we build, but how high should we build:

At what point are the significant benefits of increased density provided by building tall overtaken by the energy repercussions of height? … Just as we pushed the structural boundaries of height, we must now continue to push the boundaries of environmental engineering in order to progress the tall typology. For, as skyscrapers continue to multiply, their effect on our cities — visually, urbanistically, and environmentally — continues to increase exponentially.

Top photo: The Burj Khalifa tower in downtown Dubai. (Reuters/Jumana El-Heloueh)

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