Yasmin Sabina Khan

One World Trade Center (1WTC) in New York, originally known as the Freedom Tower, has become “The Top of America,” as this week’s issue of Time magazine puts it. According to the Council on Tall Buildings and Urban Habitat (CTBUH), the organization that determines how a building’s height is measured, 1WTC’s height to architectural top is 1,776 feet. This includes the 408-foot-tall spire that rises above the main structure of the building. In announcing the CTBUH decision to include the spire in its measurement, the organization’s executive director noted the symbolic importance of the spire reaching to 1,776 feet and the Height Committee’s confidence that the spire will remain a permanent architectural feature of the building.

So, the Sears Tower (now Willis Tower) in Chicago has lost its title as the tallest building in North America (it was the World’s Tallest Building from its completion in 1974 to 1996, when it lost that title to the Petronas Towers). The main roof level at the top of the building structure is actually higher at the Willis Tower in Chicago than at 1WTC: 1,451 feet at the Willis Tower vs. 1,368 feet to the steel parapet at 1WTC. But since the late 1990s the CTBUH has evaluated buildings according to several measurements, with height to architectural top determining the official building height. Initially there were four measurement categories; these have been reduced to three, eliminating the height to roof measurement.

The current three categories of measurement are:

1. Height to architectural top. Permanent spires are included in this measurement. 1WTC’s height to architectural top is 1,776 feet; the Willis Tower’s height to architectural top is 1,451 feet.
2. Height to highest occupied floor. 1WTC’s highest occupied floor is at 1,268 feet; the Willis Tower’s highest occupied floor is at 1,354 feet.
3. Height to tip. This measurement includes antennas. 1WTC’s height to tip is 1,792 feet; the Willis Tower’s height to tip measures 1,729 feet.