Debate rages over whether the 125m spire counts as part of the building. Do you know your antenna from your radome?

One World Trade Center rises above the lower Manhattan skyline. Photograph: Mark Lennihan/AP

800 tonnes of steel was set to be hauled into place at the top of One World Trade Center on Monday, eventually crowning the glassy shaft with a 125m spire, making this the tallest building in the western hemisphere. It will rise to the symbolic height of 1,776ft (541m), the year of America's independence – a touch of PR genius dreamt up by the building's original architect, Daniel Libeskind, which he announced to assembled gasps on the Oprah Winfrey show in 2003.

Ten years on, Libeskind's splintered vortex of shards has been replaced by a blandly corporate obelisk by SOM, predicted to be the most expensive office building in the world, at $3.8bn. But it retains the all-important numerology of 1776.

Monday's weather didn't co-operate, the steely spire was not raised, and the building still stands at around 415m – already New York's tallest building, but less than half that of the tallest in the world, Dubai's Burj Khalifa. The lift will be attempted again today, but the spire will not be assembled for some time – and even then, doubts remain as to whether this shiny needle actually counts as a part of the building's total height: the crucial definition being whether it is an antenna or a spire.

This strange debate flared up last May, when the design of the mast was changed, removing the cladding of the "radome" (short for radar dome), and saving around $20m. SOM had originally designed a decorative sheath of interlocking triangles of fibreglass and steel, 7m at its widest point. Without the cladding, the mast is left exposed as a straightforward pole of steel trusses, about 2m wide and intersected by wider maintenance platforms.

Aspiring ambition … Will the mast count without its cladding? Image: One World Trade Center

"This definitely raises questions," said Kevin Brass, the public affairs manager for the Council on Tall Buildings and Urban Habitat, the body that passes official judgment on such things as whether your erection is tall, supertall or megatall. "Our criteria are very specific. We include spires and not antennas. If this is an antenna, it won't be part of the height measurement. The cladding was an integral part of the design and made the extension part of the permanent look and feel of the building."

You might think that measuring the height of a building is a fairly straightforward task. Not so for the Council on Tall Buildings. The non-profit agency has three different methods for determining how high a tower actually is, from the Height to the Architectural Top, to the Highest Occupied Floor, to the Height to Tip. The first is the yardstick it uses to compile its World's Tallest Buildings List – and will determine if One World Trade Center truly meets its claim.

The Council has yet to reach a decision, as it has not received the final construction drawings of the project. Once the papers are sent, a "height committee" will be convened to make the final judgment as to whether the spire does indeed count as a piece of architecture or not. If not, One World Trade Center will only be the third tallest building in America, trumped by both the Willis (formerly Sears) Tower in Chicago, which stands at 527m, and (somewhat appropriately) by the Trump International Hotel and Tower, also in Chicago. Even with its spire, it will not reach the height of Mecca's 600m clock-tower in Saudi Arabia, where the 1km Kingdom Tower is also being planned in Jeddah to overshadow them all.

Such details are of little concern to the developer: "If truth be told, this discussion is irrelevant," said Steve Coleman, spokesman for the Port Authority of New York and New Jersey. "One WTC will be the tallest building in the Western Hemisphere." But for how long remains to be seen. Perhaps they should have opted for a telescopic mast.

via the guardian

http://www.guardian.co.uk/artanddesign/architecture-design-blog/2013/may/02/one-world-trade-centre-tallest-building