The new World Trade Center tower in New York knocked Chicago's Willis Tower off its pedestal as the tallest building in the U.S. when an international panel of architects announced Tuesday that the needle atop the New York skyscraper that is set to open next year can be counted when measuring the structure's height.

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One World Trade Center, the main tower on the rebuilt site, is still under construction and is due to open next year. (Kathy Willens/Associated Press)

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The height committee of the Council on Tall Buildings and Urban Habitat said the needle is not an antenna but a spire, and thus is a permanent part of the building. The World Trade Center's needle, measuring 124 metres, was more than enough to knock down the Chicago building formerly known as the Sears Tower to second place, in a decision made by a Chicago-based panel.

"The committee was well aware of the gravity of the situation," Antony Wood, the council's executive director, said during a news conference.

With the needle, 1 World Trade Center is 541 metres tall, a height that when calculated in feet (1,776) is meant to symbolize America's founding year: 1776. Without it, the building would have been well short of the 442-metre Willis Tower.

Height committee has final word

Dubai's Burj Khalifa is the tallest building in the world at 828 metres. With Tuesday's decision, the Willis Tower will be the 10th-tallest and the new World Trade Center will be the third-tallest building in the world.

At stake was more than just bragging rights in two cities that feast on superlatives and the tourist dollars that might follow: 1 World Trade Center stands as a monument to those killed in the Sept. 11, 2001, attacks, which destroyed the two signature towers of the original World Trade Center that had been a distinct feature of the Manhattan skyline since the 1970s.

The building's 417 metre height without the needle is also symbolic: it is the height of the original World Trade Center.

Willis Tower

Chicago's Willis Tower, formerly the Sears Tower, is no longer the tallest building in America at 442-metres. (Charles Rex Arbogast/Associated Press)

The 30 members of the height committee are industry professionals from all over the world and the committee is widely recognized as the final arbiter of official building heights around the world. They conferred behind closed doors last week in Chicago, where the world's first skyscraper was completed in 1884.

Broadcast antennas don't count in height

The new World Trade Center tower remains under construction and is expected to open next year.

The designers originally had intended to enclose the mast's communications gear in decorative cladding made of Fiberglas and steel. But the developer removed that exterior shell from the design, saying it would be impossible to properly maintain or repair. Without it, the question was whether the mast was now primarily just a broadcast antenna.

Under the council's current criteria, spires that are an integral part of a building's aesthetic design count. Broadcast antennas that can be added and removed do not.

Daniel Safarik, an architect and spokesman for the nonprofit council, said it might consider amending its height criteria. Such a move would have much broader implications that could force a reshuffle in the rankings of the tallest buildings in the world.