According to David Childs of Skidmore, Owings and Merrill, the project architect of the new 1 World Trade Center, the tower:
... will be a symbol of the entire project, as well as marking the memorial, and it occupies a very important piece of New York City property: the sky.
We really wanted our design to be grounded in something that was very real, not just in sculptural sketches. We explored the infrastructural challenges because the proper solution would have to be compelling, not just beautiful. The design does have great sculptural implications, and we fully understand the iconic importance of the tower, but it also has to be a highly efficient building. The discourse about Freedom Tower has often been limited to the symbolic, formal and aesthetic aspects but we recognize that if this building doesn't function well, if people don't want to work and visit there, then we will have failed as architects.
Design
One World Trade Center's design includes 2,600,000 square feet (242,000 m2) of office space, as well as an observation deck, parking and broadcast and antenna facilities, all supported by both above and below-ground mechanical infrastructure for the building and its adjacent public spaces. Below-ground tenant parking and storage, shopping and access to the PATH and subway trains and the World Financial Center are also provided.
A 65-foot (20 m) high public lobby, topped by a series of mechanical floors, form a 200-foot (61 m)-per-side visual cubic base to the tower. The next 69 floors, providing tenant office space, rise above the base to an elevation of 1,150 feet (350 m). Mechanical and observation floors culminate in a rooftop observation deck at 1,362 feet (415 m) with a glass parapet extending to 1,368 feet (417 m) — the heights of the original Twin Towers. A shrouded antenna structure supported by cables, engineered by Schlaich Bergermann & Partner, rises to a total height of 1,776 feet (541 m), which is a tribute to the year the United States Declaration of Independence was signed. A plan to build a restaurant near the top of the tower was abandoned as logistically too difficult.
The 200-foot (61 m) sides at the square footprint of the base are almost as wide as the 208-foot (63 m) square of the original Twin Towers. The 185-foot (56 m) window-less concrete base was added to the design in 2005 to increase strength to withstand a truck bomb, and the building was moved further from the West Side Highway. The design was criticized as uninviting and fortress-like. To address this, the base was to be clad in more than 2,000 pieces of prismatic glass designed to draw upon the themes of motion and light.This proved unworkable, however, and a simpler glass facade is planned for the base. Cable-net glass facades on all four sides of the building for the higher floors, designed by Schlaich Bergermann, will be consistent with the other buildings in the complex. They measure 60 feet (18 m) high and range in width from 30 feet (9.1 m) on the east and west sides (for access to the observation deck) to 50 feet (15 m) on the north side and 70 feet (21 m) on the south for primary tenant access. The curtain wall is being manufactured and assembled in Portland, Oregon by Benson Industries using glass made in Minnesota by Viracon.
As the tower rises from this cubic base, its square edges are chamfered back, transforming the square into eight tall isosceles triangles in elevation, or an elongated square antiprism. At its middle, the tower forms a perfect octagon in plan and then culminates in a glass parapet (elevation 1,362 feet (415 m) and 1,368 feet (417 m)) whose plan is a square, rotated 45 degrees from the base. A mast containing the antenna for television broadcasters – designed by a collaboration among SOM, artist Kenneth Snelson (who invented the tensegrity structure), lighting designers and engineers – is secured by a system of cables, and rises from a circular support ring, similar to the Statue of Liberty's torch, to a height of 1,776 feet (541 m). Above the mast will be an intense beam of light that will be lit at night and will likely be visible over 1,000 feet (300 m) into the air above the tower.
New safety features will include 3 feet (91 cm) thick reinforced concrete walls for all stairwells, elevator shafts, risers, and sprinkler systems; extremely wide "emergency stairs"; a dedicated set of stairwells exclusively for the use of firefighters; and biological and chemical filters throughout its ventilation system. The building will no longer be 25 feet (8 m) away from West Street, as the Twin Towers were. At its closest point, West Street will be 65 feet (20 m) away. The windows on the side of the building facing in this direction will be equipped with specially tempered blast-resistant plastic, which will look nearly the same as the glass used in the other sides of the building. The seventy elevators and 9 escalators for 1 World Trade Center will be provided by ThyssenKrupp, with steel counterweights supplied by Concord Steel. The Port Authority has stated: "Its structure is designed around a strong, redundant steel moment frame consisting of beams and columns connected by a combination of welding and bolting. Paired with a concrete-core shear wall, the moment frame lends substantial rigidity and redundancy to the overall building structure while providing column-free interior spans for maximum flexibility."
1 World Trade Center will be green in several ways. Although the roof area of any tower is comparatively limited, the building will implement a rainwater collection and recycling scheme for its cooling systems. The building's fuel cell will generate 4.8 million watts (MW), and waste steam will help generate electricity. One World Trade Center is expected to receive a Gold Certification by Leadership in Energy and Environmental Design. Like all of the new facilities at the World Trade Center site, One World Trade Center will be heated by steam, with limited oil or natural gas utilities located on site.
Close to the building are the below-ground memorials featuring two glass reflecting pools. These pools are approximately 30 feet (9.1 m) below the surface, and are located on the exact locations of the former Twin Towers. The pools are intended to fill out the "footprint" of the towers, each being equal to the exact perimeter of the North and South Tower. Trees surround the area containing the pools, and the area is intended to be a contemplative and quiet area separated from the city. The names of the nearly 3,000 victims of the attacks on September 11, 2001 and 1993 World Trade Center Bombing will be inscribed in bronze and placed around each pool. Under the pools, there will be a museum of the World Trade Center attacks, called the National September 11 Memorial & Museum. The memorial is scheduled to be completed by September 11, 2011, the tenth anniversary of the attacks on the World Trade Center.
Height
The roof (including a 33 ft 4 in (10.16 m) parapet) of the top floor of One World Trade Center will be 1,368 feet (417 m), the same as the original One World Trade Center. With its spire height (the criteria of two categories of the Council on Tall Buildings and Urban Habitat), One World Trade Center will stand at 1,776 feet (541 m), a figure symbolic of the year of the United States Declaration of Independence.
With a structural height of 1,776 feet (541 m), One World Trade Center will surpass the 1,671 feet (509 m) height of Taipei 101 to become the world's tallest all-office building and the tallest building in the Americas, surpassing the Willis Tower (formerly known as the Sears Tower) in Chicago. However, its roof height will still be 83 feet (25 m) shorter than the Willis Tower. When completed, One World Trade Center will be the third tallest building in the world, behind the Burj Khalifa and the Mecca Royal Hotel Clock Tower.
The Chicago Spire (with a planned height of 2,000 feet (610 m)) was expected to exceed the height of One World Trade Center, but its construction was cancelled in 2009 due to financial difficulties. A new 2000 ft+ tower is currently planned in Chicago's Old Post Office Redevelopment project.
The World Trade Center's South Tower had an outdoor rooftop observation deck at 1,380 feet (420 m) and another indoor observation deck at 1,310 feet (400 m). One World Trade Center's indoor observation deck will be at a height of approx 1,313 feet (400 m).
Space allotment and security
One World Trade Center will have a top floor denoted as 82. The first office floor of the building atop the 200-foot (61 m) square base will be designated as Floor 20, and the building will have 74 usable above-ground floors. Sixty-nine floors will be designated as office floors. Additionally, roughly 55,000 square feet (5,100 m2) of retail space will exist below-grade, part of an overall 500,000 square feet (46,000 m2) of retail space to be spread throughout the site both in the below-grade concourses and on the lower floors of Towers 2, 3, and 4.
In addition to the protection offered by the reinforced, window-less base, a number of other design and security features are planned for the building. For example, all vehicles will be screened before they enter the site via the underground roadway, including for radioactive materials. Visitors to the September 11 memorial will undergo an airport-style screening. 400 closed-circuit surveillance cameras will be placed in and around the trade center site. Live feeds will be monitored around the clock by the NYPD, and a computer system will use "video analytic" computer software designed to detect potential threats like unattended bags and retrieve images based on descriptions of terror or other criminal suspects. New York City and Port Authority police will patrol the site.
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