New York, US | 2002


Designed as part of the competition for a master plan for the site of the former World Trade Center towers, the scheme proposed by a project-specific team called United Architects, whose members have offices in the United States and abroad, is actually five linked towers containing over ten million square feet of space. More than eighty percent of the area is designated for office space; the balance is residential, commercial, and cultural. The towers rise over a proposed memorial at ground level as well as an elaborate transportation and retail complex grade. The ambition of this team in designing the project is clear:" The structural concept for the towers has been developed with the intention of establishing a new tower typology." The principal elements of each tower are twenty-foot-square concrete core and two or more volumes of habitable space, which wrap around the core. The supporting framework for the volumes of space is a diagonally braced exterior skin, which in effect, makes the spaces structural "tubes within tubes" without intervening columns. The geometric flexibility and strength of the triangulated structural skin allows the exterior tubes to expand and contract as they wrap around the core, producing the dynamic appearance of the enemble. Each of the five towers is designed as a self-supporting freestanding structure. When they are conjoined, their individual structural strength is increased, making them able to resist tremendous forces trough mutual support. In the wake of the September 11 disaster and the public's concerns about the safety of tall buildings, the added strength is an important feature, but is not the only design element created by the bundling of the towers. The conjoined towers, unlike the traditional vertical tower with its unitary vertical systems, offer multiple routes of escape and firefighting access following vertical and, if necessary, horizontal routes. This redundancy of circulation can also be found in other systems in the building. For example, the network of sprinkler heads can have multiple sources of water pressure, and in the event of the failure of one another can compensate. The designers have also tried to restore a sense of safety as well as a sense of wonder in tall buildings. A "sky park" at the top of the complex, with public amenities, creates a lofty horizon at the fifty-fifth floor. The sky park links all of the towers and brings public access and social space to the highest common point of the five structures. At floor 108, the apex of the tallest structure, is an observatory. "sky gardens" on the roofs of the towers provide further social amenity as well as positive environmental effects. The connections between the towers create a remarkable silhouette across the skyline, a symbol of collectivity; their gaps also create monumental urban spaces that frame views and channel circulation. Together, the ensemble inspires wonder at its soaring height; but the towers also arc in such a way as to create public space beneath them. The project celebrates the tall building as a technical and cultural artifact.

Project Info

In Collaboration with United Architects: Greg Lynn FORM – UNStudio – Kevin Kennon - FOA – Reiser+Umemoto  |  Type: Mixed-Use Highrise  |  Sponsor: Lower Manhattan Development Corp. Invited International Competition, 6 Teams  |  Height: 1,620 Feet (494 Meters) High  |  Structure: Concrete Core and Diagonally Braced Skin, Tube within Tube


Project Credits


Jesse Reiser + Nanako Umemoto


Design Team

Rhett Russo, Eva Perez de Vega Steele, Wolfgang Gollwitzer, Jason Scroggin, Stephan Vary, Josh McKeown, Akari Takebayashi


Interns and Assistants

Kenji Nonobe, Hidekazu Ota


Structural Engineer

ARUP, 77 Water St, New York NY 10005 USA

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