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Doubts over whether New York's new One World Trade Centre will be the US's tallest tower

The One World Trade Centre's crown as the country's tallest building is at risk Photo: APTN

A change to the design of a needle that will sit on top of One World Trade Center is raising questions over whether the building will still be America's tallest when completed.

The 408-foot-tall needle will no longer be enclosed in a fiberglass-and-steel enclosure called a radome, a feature that was recently removed from the original design because the building's developer says it would be impossible to properly maintain or repair it.

The latest artist rendering of One World Trade Center, released this week, shows an antenna in place of the spire.

The Council on Tall Buildings and Urban Habitat, a Chicago-based organization considered an authority on such records, says antennas do not count when determining building height.

An antenna, the group says, is something simply added to the top of a tower that can be removed. By contrast, a spire is something that is part of the building's architectural design.

Timothy Johnson, Chairman of the Council of Tall Buildings and Urban Habitat, explains:

Without the enclosure, it's unclear whether the needle is an antenna or a spire, a crucial distinction in terms of measuring the building's height. Without the spire, One World Trade Center would actually be shorter than the Willis Tower in Chicago, which currently wears the crown of tallest building in the U.S. at 1,451 feet, not including its own antennas.

Last week, the skyscraper became New York City's tallest building as workers erected steel columns that were just high enough to rise above the Empire State Building's observation deck.

The building is being constructed to replace the twin towers destroyed in the Sept. 11, 2001, terror attacks.

In order to repair or replace a broken panel on the needle's proposed enclosure, a climber would have to scale the spire, attach a cable to the top, lower the cable about 2,000 feet down, and then use it to hoist a 2,000-pound piece of fiberglass back to the top, said Jordan Barowitz, a spokesman for Douglas Durst, the building's developer.

Designs call for the tower's roof to stand at 1,368 feet (416.97 meters), the same height as the north tower of the original World Trade Center. With the needle, the building's total height will be a symbolic 1,776 feet, referring to America's founding in 1776.

Experts and architects have long disagreed about how to measure the height of skyscrapers that have masts, spires and antennas that stretch into the sky.