One World Trade Center, the giant monolith being built to replace the twin towers destroyed in the Sept. 11 attacks, laid claim to the title of New York City's tallest skyscraper today.

Workers erected steel columns that made its unfinished skeleton a little over 1,250 feet high, just enough to clear the roof of the observation deck on the Empire State Building.

The milestone is a preliminary one. Workers are still adding floors to the so-called "Freedom Tower" and it isn't expected to reach its full height for at least another year, at which point it is likely to be declared the tallest building in the United States and third tallest in the world.

However, those bragging rights will carry an asterisk: Crowning the world's tallest buildings is a little like picking the heavyweight champion in boxing. There is often disagreement about who deserves the belt. In this case, the issue involves the 408-foot needle that will sit atop the tower.

Count it, and the World Trade Center is back on top. Otherwise, it will have to settle for No. 2, after the Willis Tower (formerly the Sears Tower) in Chicago.

"Height is complicated," said Nathaniel Hollister, a spokesman for the Council on Tall Buildings and Urban Habitats, a Chicago-based organization considered an authority on such records.

Experts and architects have long disagreed about where to stop measuring super-tall buildings outfitted with masts, spires and antennas that extend far above the roof.

Consider the case of the Empire State Building: Measured from the sidewalk to the tip of its needle-like antenna, the granddaddy of all super-tall skyscrapers actually stands 1,454 feet high, well above the mark surpassed by One World Trade Center on Monday.

Should antennas count?

Purists say antennas shouldn't count when determining building height.

Workers ride an elevator in the building that on Monday became New York City's tallest. (David Common/CBC)

An antenna, they say, is more like furniture than a piece of architecture. Like a chair sitting on a rooftop, an antenna can be attached or removed. The Empire State Building didn't even get its distinctive antenna until 1952. The record books, as the argument goes, shouldn't change every time someone installs a new satellite dish.

Excluding the antenna brings the Empire State Building's total height to 1,250 feet. That was still high enough to make the skyscraper the world's tallest from 1931 until 1972.

Neither of the Willis Tower nor One World Trade are as high as the CN Tower, in Toronto, which stands at 1,815 feet. However, it isn't considered a building at all by most record-keepers, because it is a television broadcast antenna and observation platform with little interior space.

As for the world's tallest building, the undisputed champion is the Burj Khalifa, in Dubai, which opened in 2010 and reaches 2,717 feet — not counting about five feet of aircraft lights and other equipment perched on top, of course.