Chicago’s Willis Tower can no longer lay claim to being the tallest building in the U.S.
The Council on Tall Buildings and Urban Habitat convened its Height Committee to rule on the official height of One World Trade Center (1WTC) in New York. The committee reached a consensus that the New York building’s height to its architectural top is 1,776 feet.
The two issues regarding the true height of the building were:
- The nature of the mast structure on top of the tower.
- The datum line (bottom point) from which the height to architectural top was determined.
Due to design changes that resulted in the removal of the architectural cladding around the mast at the top of the structure, it became unclear whether the structure was in fact a “spire” – a vertical element that completes the architectural expression of the building and is intended as permanent, or whether it was an antenna – a piece of functional-technical equipment that was subject to change.
The spire-antenna distinction makes a difference in the measurement of “height to architectural top,” which includes spires but does not include antennae, signage, flag poles or other functional-technical equipment. Determining the topmost structure to be “functional-technical” potentially could have significantly impacted 1WTC’s ranking against other buildings, as the next obvious point to take a measurement of “architectural top” would have been the building’s roof slab, at 1,334 feet, 8 inches – 441 feet, 4 inches lower than claimed.
“We were very satisfied with the detailed information presented by the team, in particular, that which affirmed that the structure on top of the building is meant as a permanent architectural feature, not a piece of functional-technical equipment,” said Timothy Johnson, Chairman of CTBUH and Design Partner at NBBJ.
The second issue at 1WTC was the location from which the 1,776-foot measurement had been taken. The building has four entrances, one on each side. Three of those entrances are flush with the 9/11 Memorial Plaza, which is level with the base of the original World Trade Center towers. These three entrances lead directly into the elevator lobby, while a fourth entrance is 5 feet, 8 inches lower than the lobby, on Vesey Street, due to the change in grade from south to north. If measured from this point, the height to architectural top would have been 1,781 feet, 8 inches.
A presenter showed plans indicating that the main entrance of the building was the south entrance facing the 9/11 Memorial plaza, and that the north entrance at the lower elevation does not provide direct access to the elevators, but requires negotiating steps or using a disabled-access lift to ascend to the lobby. To be considered “significant,” an entrance must “be predominantly above existing or pre-existing grade and permit access to one or more primary uses in the building via elevators.” Therefore, the lower Vesey Street (north) entrance was not considered “significant” by the committee.
Upon completion, the building is expected to be the world’s third tallest building.