The World Trade Center was a large complex of seven buildings in Lower Manhattan, New York City, United States. It featured landmark twin towers, which opened on April 4, 1973, and were destroyed in the September 11 attacks, with 7 World Trade Center collapsing later that day due to the damage it suffered when the twin towers collapsed that morning. The other buildings in the complex were severely damaged by the collapse of the twin towers, and their ruins were eventually demolished.
At the time of their completion, the “Twin Towers” — the original 1 World Trade Center, at 1,368 feet (417 m); and 2 World Trade Center, at 1,362 feet (415 m) — were the tallest buildings in the world. The other buildings in the complex included the Marriott World Trade Center (3 WTC), 4 WTC, 5 WTC, 6 WTC, and 7 WTC. All these buildings were built between 1975 and 1985, with a construction cost of $400 million ($2,300,000,000 in 2014 dollars). The complex was located in New York City’s Financial District and contained 13,400,000 square feet (1,240,000 m2) of office space.
Before The World Trade Center
The western portion of the World Trade Center site was originally under the Hudson River, with the shoreline in the vicinity of Greenwich Street. It was on this shoreline close to the intersection of Greenwich and the former Dey Street that Dutch explorer Adriaen Block’s ship, the Tyger, burned to the waterline in November 1613, stranding Block and his crew and forcing them to overwinter on the island. They built the first European settlement in Manhattan. The remains of the ship were buried under landfill when the shoreline was extended starting in 1797, and were discovered during excavation work in 1916. The remains of a second ship from the eighteenth century were discovered in 2010 during excavation work at the site. The ship, believed to be a Hudson River sloop, was found just south of where the Twin Towers used to stand, about 20 feet below the surface.
Later, the area became Radio Row. New York City’s Radio Row, which existed from 1921 to 1966, was a warehouse district on the Lower West Side in the Financial District. Harry Schneck opened City Radio on Cortlandt Street in 1921, and eventually the area held several blocks of electronics stores, with Cortlandt Street as its central axis. The used radios, war surplus electronics (e.g., ARC-5 radios), junk, and parts often piled so high they would spill out onto the street, attracting collectors and scroungers. According to a business writer, it also was the origin of the electronic component distribution business.
The idea of establishing a World Trade Center in New York City was first proposed in 1943. The New York State Legislature passed a bill authorizing New York Governor Thomas E. Dewey to begin developing plans for the project but the plans were put on hold in 1949. During the late 1940s and 1950s, economic growth in New York City was concentrated in Midtown Manhattan. To help stimulate urban renewal in Lower Manhattan, David Rockefeller suggested that the Port Authority build a World Trade Center in Lower Manhattan.
Plans for the use of eminent domain to remove the shops in Radio Row bounded by Vesey, Church, Liberty, and West Streets began in 1961 when the Port Authority of New York and New Jersey was deciding to build the world’s first world trade center. They had two choices: the east side of Lower Manhattan, near the South Street Seaport; and the west side, near the H&M station, Hudson Terminal. Initial plans, made public in 1961, identified a site along the East River for the World Trade Center. As a bi-state agency, the Port Authority required approval for new projects from the governors of both New York and New Jersey. New Jersey Governor Robert B. Meyner objected to New York getting a $335 million project. Toward the end of 1961, negotiations with outgoing New Jersey Governor Meyner reached a stalemate.
At the time, ridership on New Jersey’s Hudson and Manhattan Railroad (H&M) had declined substantially from a high of 113 million riders in 1927 to 26 million in 1958 after new automobile tunnels and bridges had opened across the Hudson River. In a December 1961 meeting between Port Authority director Austin J. Tobin and newly elected New Jersey Governor Richard J. Hughes, the Port Authority offered to take over the Hudson & Manhattan Railroad to have it become the Port Authority Trans-Hudson (PATH). The Port Authority also decided to move the World Trade Center project to the Hudson Terminal building site on the west side of Lower Manhattan, a more convenient location for New Jersey commuters arriving via PATH. With the new location and Port Authority acquisition of the H&M Railroad, New Jersey agreed to support the World Trade Center project. In compensation for Radio Row business owners’ displacement, the PANYNJ gave each business $3,000 each, without regard to how long the business had been there or how prosperous the business was. After the area had been purchased for the World Trade Center in March 1964, Radio Row was demolished starting in March 1965. It was completely demolished by 1966.
Approval was also needed from New York City Mayor John Lindsay and the New York City Council. Disagreements with the city centered on tax issues. On August 3, 1966, an agreement was reached that the Port Authority would make annual payments to the City in lieu of taxes for the portion of the World Trade Center leased to private tenants. In subsequent years, the payments would rise as the real estate tax rate increased.
On September 20, 1962, the Port Authority announced the selection of Minoru Yamasaki as lead architect and Emery Roth & Sons as associate architects. Yamasaki devised the plan to incorporate twin towers; Yamasaki’s original plan called for the towers to be 80 stories tall, but to meet the Port Authority’s requirement for 10,000,000 square feet (930,000 m2) of office space, the buildings would each have to be 110 stories tall.
Yamasaki’s design for the World Trade Center, unveiled to the public on January 18, 1964, called for a square plan approximately 208 feet (63 m) in dimension on each side. The buildings were designed with narrow office windows 18 inches (46 cm) wide, which reflected Yamasaki’s fear of heights as well as his desire to make building occupants feel secure. Yamasaki’s design included building facades sheathed in aluminum-alloy. The World Trade Center was one of the most-striking American implementations of the architectural ethic of Le Corbusier, and it was the seminal expression of Yamasaki’s gothic modernist tendencies.
A major limiting factor in building height is the issue of elevators; the taller the building, the more elevators are needed to service the building, requiring more space-consuming elevator banks. Yamasaki and the engineers decided to use a new system with two “sky lobbies”—floors where people could switch from a large-capacity express elevator to a local elevator that goes to each floor in a section. This system, inspired by the local-express train operation that the New York City Subway system used, allowed the design to stack local elevators within the same elevator shaft. Located on the 44th and 78th floors of each tower, the sky lobbies enabled the elevators to be used efficiently, increasing the amount of usable space on each floor from 62 to 75 percent by reducing the number of elevator shafts. Altogether, the World Trade Center had 95 express and local elevators.
The structural engineering firm Worthington, Skilling, Helle & Jackson worked to implement Yamasaki’s design, developing the tube-frame structural system used in the twin towers. The Port Authority’s Engineering Department served as foundation engineers, Joseph R. Loring & Associates as electrical engineers, and Jaros, Baum & Bolles as mechanical engineers. Tishman Realty & Construction Company was the general contractor on the World Trade Center project. Guy F. Tozzoli, director of the World Trade Department at the Port Authority, and Rino M. Monti, the Port Authority’s Chief Engineer, oversaw the project. As an interstate agency, the Port Authority was not subject to local laws and regulations of the City of New York, including building codes. Nonetheless, the structural engineers of the World Trade Center ended up following draft versions of the new 1968 building codes.
The tube-frame design, earlier introduced by Fazlur Khan, was a new approach that allowed more open floor plans than the traditional design that distributed columns throughout the interior to support building loads. The World Trade Center towers used high-strength, load-bearing perimeter steel columns called Vierendeel trusses that were spaced closely together to form a strong, rigid wall structure, supporting virtually all lateral loads such as wind loads, and sharing the gravity load with the core columns. The perimeter structure containing 59 columns per side was constructed with extensive use of prefabricated modular pieces, each consisting of three columns, three stories tall, connected by spandrel plates.
The spandrel plates were welded to the columns to create the modular pieces off-site at the fabrication shop. Adjacent modules were bolted together with the splices occurring at mid-span of the columns and spandrels. The spandrel plates were located at each floor, transmitting shear stress between columns, allowing them to work together in resisting lateral loads. The joints between modules were staggered vertically, so that the column splices between adjacent modules were not at the same floor.
The core of the towers housed the elevator and utility shafts, restrooms, three stairwells, and other support spaces. The core of each tower was a rectangular area 87 by 135 feet (27 by 41 m) and contained 47 steel columns running from the bedrock to the top of the tower. The large, column-free space between the perimeter and core was bridged by prefabricated floor trusses. The floors supported their own weight as well as live loads, providing lateral stability to the exterior walls and distributing wind loads among the exterior walls. The floors consisted of 4 inches (10 cm) thick lightweight concrete slabs laid on a fluted steel deck. A grid of lightweight bridging trusses and main trusses supported the floors. The trusses connected to the perimeter at alternate columns and were on 6 foot 8 inch (2.03 m) centers. The top chords of the trusses were bolted to seats welded to the spandrels on the exterior side and a channel welded to the core columns on the interior side. The floors were connected to the perimeter spandrel plates with viscoelastic dampers that helped reduce the amount of sway felt by building occupants.
Hat trusses (or “outrigger truss”) located from the 107th floor to the top of the buildings were designed to support a tall communication antenna on top of each building. Only 1 WTC (north tower) actually had an antenna fitted; it was added in 1978. The truss system consisted of six trusses along the long axis of the core and four along the short axis. This truss system allowed some load redistribution between the perimeter and core columns and supported the transmission tower.
The tube frame design, using steel core and perimeter columns protected with sprayed-on fire resistant material, created a relatively lightweight structure that would sway more in response to the wind compared to traditional structures, such as the Empire State Building that have thick, heavy masonry for fireproofing of steel structural elements. During the design process, wind tunnel tests were done to establish design wind pressures that the World Trade Center towers could be subjected to and structural response to those forces. Experiments also were done to evaluate how much sway occupants could comfortably tolerate; however, many subjects experienced dizziness and other ill effects. One of the chief engineers Leslie Robertson worked with Canadian engineer Alan G. Davenport to develop viscoelastic dampers to absorb some of the sway. These viscoelastic dampers, used throughout the structures at the joints between floor trusses and perimeter columns along with some other structural modifications, reduced the building sway to an acceptable level.
The structural engineers on the project also considered the possibility that an aircraft could crash into the building. In July 1945, a B-25 bomber that was lost in the fog had crashed into the 79th floor of the Empire State Building. A year later, another airplane nearly crashed into the 40 Wall Street building, and there was another near-miss at the Empire State Building. In designing the World Trade Center, Leslie Robertson considered the scenario of the impact of a jet airliner, the Boeing 707, which might be lost in the fog, seeking to land at JFK or at Newark airports. The National Institute of Standards and Technology (NIST) found a three page white paper that mentioned another aircraft impact analysis, involving impact of a jet at 600 mph (970 km/h), was indeed considered, but the original documentation of the study was lost when Port Authority offices were destroyed in the collapse of the World Trade Center.
Sprayed-fire resistant materials (SFRMs) were used to protect some structural steel elements in the towers, including all floor trusses and beams. Gypsum wallboard in combination with SFRMs, or in some cases gypsum wallboard alone, was used to protect core columns. Vermiculite plaster was used on the interior-side and SFRMs on the other three sides of the perimeter columns for fire protection. The 1968 New York City building codes were more lenient in some aspects of fire protection, such as allowing three exit stairwells in the World Trade Center towers, instead of six as required under older building codes.
In April 1970, the New York City Department of Air Resources ordered contractors building the World Trade Center to stop the spraying of asbestos as an insulating material.
More fireproofing was added after a fire in February 1975 that spread to six floors before being extinguished. After the 1993 bombing, inspections found fireproofing to be deficient. The Port Authority was in the process of replacing it, but replacement had been completed on only 18 floors in WTC 1, including all the floors affected by the aircraft impact and fires on September 11, and on 13 floors in WTC 2, although only three of these floors (77,78, and 85) were directly affected by the aircraft impact.
The 1968 New York City building codes did not require sprinklers for high-rise buildings, except for underground spaces. In accordance with building codes, sprinklers were originally installed only in the underground parking structures of the World Trade Center. Following a major fire in February 1975, the Port Authority decided to start installing sprinklers throughout the buildings. By 1993, nearly all of 2 WTC and 85 percent of 1 WTC had sprinklers installed, and the entire complex was retrofitted by 2001.
In March 1965, the Port Authority began acquiring property at the World Trade Center site. Demolition work began on March 21, 1966, to clear thirteen square blocks of low rise buildings in Radio Row for construction of the World Trade Center. Groundbreaking for the construction of the World Trade Center took place on August 5, 1966.
The site of the World Trade Center was located on landfill with the bedrock located 65 feet (20 m) below. To construct the World Trade Center, it was necessary to build a “bathtub” with a slurry wall around the West Street side of the site, to keep water from the Hudson River out. The slurry method selected by Port Authority’s chief engineer, John M. Kyle, Jr., involved digging a trench, and as excavation proceeded, filling the space with a “slurry” mixture composed of bentonite and water, which plugged holes and kept groundwater out. When the trench was dug out, a steel cage was inserted and concrete was poured in, forcing the “slurry” out. It took fourteen months for the slurry wall to be completed. It was necessary before excavation of material from the interior of the site could begin. The 1,200,000 cubic yards (920,000 m3) of material excavated were used (along with other fill and dredge material) to expand the Manhattan shoreline across West Street to form Battery Park City.
In January 1967, the Port Authority awarded $74 million in contracts to various steel suppliers, and Karl Koch was hired to erect the steel. Tishman Realty & Construction was hired in February 1967 to oversee construction of the project. Construction work began on the North Tower in August 1968; construction on the South Tower was underway by January 1969. The original Hudson Tubes, carrying PATH trains into Hudson Terminal, remained in service as elevated tunnels during the construction process until 1971 when a new PATH station opened.
The topping out ceremony of 1 WTC (North Tower) took place on December 23, 1970, while 2 WTC’s ceremony (South Tower) occurred later on July 19, 1971. The first tenants moved into the North Tower on December 15, 1970; the South Tower accepted tenants in January 1972. When the World Trade Center twin towers were completed, the total costs to the Port Authority had reached $900 million. The ribbon cutting ceremony was on April 4, 1973.
In addition to the twin towers, the plan for the World Trade Center complex included four other low-rise buildings, which were built in the early 1970s. The 47-story 7 World Trade Center building was added in the 1980s, to the north of the main complex. Altogether, the main World Trade Center complex occupied a 16-acre (65,000 m2) superblock.
On a typical weekday 50,000 people worked in the towers with another 200,000 passing through as visitors. The complex was so large that it had its own zip code: 10048. The towers offered expansive views from the observation deck atop the South Tower and the Windows on the World restaurant on top of the North Tower. The Twin Towers became known worldwide, appearing in numerous movies and television shows as well as on postcards and other merchandise, and became seen as a New York icon, in the same league as the Empire State Building, Chrysler Building and the Statue of Liberty.
North and South Towers:
One World Trade Center and Two World Trade Center, commonly the Twin Towers, the idea of which was brought up by Minoru Yamasaki, were designed as framed tube structures, which provided tenants with open floor plans, uninterrupted by columns or walls. They were the main buildings of the World Trade Center. The North Tower (One World Trade Center), the tallest building in the world at 1,368 feet (417 m) by the time of its completion, began construction in 1966 with the South Tower (2 World Trade Center); extensive use of prefabricated components helped to speed up the construction process, and the first tenants moved into the North Tower in December 1970, while it was still under construction. When completed in 1973, the South Tower, Two World Trade Center (the South Tower) became the second tallest building in the world at 1,362 feet (415 m); the South Tower’s rooftop observation deck was 1,362 ft (415 m) high and its indoor observation deck was 1,310 ft (400 m) high. Each tower stood over 1,350 feet (410 m) high, and occupied about 1 acre (4,000 m2) of the total 16 acres (65,000 m2) of the site’s land. During a press conference in 1973, Yamasaki was asked, “Why two 110-story buildings? Why not one 220-story building?” His tongue-in-cheek response was: “I didn’t want to lose the human scale.”
When completed in 1972, 1 World Trade Center became the tallest building in the world for two years, surpassing the Empire State Building after a 40-year reign. The North Tower stood 1,368 feet (417 m) tall and featured a telecommunications antenna or mast that was added at the top of the roof in 1978 and stood 362 feet (110 m) tall. With the 362-foot (110 m)-tall antenna/mast, the highest point of the North Tower reached 1,730 feet (530 m). Chicago’s Sears Tower, finished in May 1973, reached 1,450 feet (440 m) at the rooftop. Throughout their existence, the WTC towers had more floors (at 110) than any other building. This number was not surpassed until the advent of the Burj Khalifa, which opened in 2010.
Top of the World observation deck:
Although most of the space in the World Trade Center complex was off-limits to the public, the South Tower featured an indoor and outdoor public observation area called Top of the World Trade Center Observatories on its 107th and 110th floors. Visitors would pass through security checks added after the 1993 World Trade Center bombing, then were sent to the 107th floor indoor observatory at a height of 1,310 feet (400 m). The columns on each face of the building were narrowed on this level to allow 28 inches of glass between them. The Port Authority renovated the observatory in 1995, then leased it to Ogden Entertainment to operate. Attractions added to the observation deck included a simulated helicopter ride around the city. The 107th floor food court was designed with a subway car theme and featured Sbarro and Nathan’s Famous Hot Dogs. Weather permitting, visitors could take two short escalator rides up from the 107th floor viewing area to an outdoor viewing platform on the 110th floor at a height of 1,377 ft (420 m). On a clear day, visitors could see up to 50 miles (80 km). An anti-suicide fence was placed on the roof itself, with the viewing platform set back and elevated above it, requiring only an ordinary railing and leaving the view unobstructed, unlike the observation deck of the Empire State Building.
Windows on the World restaurant:
The North Tower had a restaurant on its 106th and 107th floors called Windows on the World, which opened in April 1976. The restaurant was developed by Joe Baum at a cost of more than $17 million. Aside from the main restaurant, two offshoots were located at the top of the North Tower: “Hors d’Oeuvrerie” (offered a Danish smorgasbord during the day and sushi in the evening) and “Cellar in the Sky” (a small wine bar). Windows on the World also had a wine school program run by Kevin Zraly. Windows on the World was closed following the 1993 World Trade Center bombing. Upon reopening in 1996, Hors d’Oeuvrerie and Cellar in the Sky were replaced with the “Greatest Bar on Earth” and “Wild Blue”. In 2000, its last full year of operation, Windows on the World reported revenues of $37 million, making it the highest-grossing restaurant in the United States. The Skydive Restaurant, opened in 1976 on the 44th floor of the North Tower, was also operated by Windows on the World restaurant, but served only lunch.
Five smaller buildings stood around the 16 acres (65,000 m2) block. One was the 22-floor hotel, which opened in 1981 as the Vista Hotel, and in 1995 became the Marriott World Trade Center (3 WTC) at the southwest corner of the site. Three low-rise buildings (4 WTC, 5 WTC, and 6 WTC) in the same hollow tube design as the towers also stood around the plaza. 6 World Trade Center, at the northwest corner, housed the United States Customs Service and the U.S. Commodities Exchange. 5 World Trade Center was located at the northeast corner above the PATH station and 4 World Trade Center was at the southeast corner. In 1987, a 47-floor office building called 7 World Trade Center was built north of the block. Beneath the World Trade Center complex was an underground shopping mall, which in turn had connections to various mass transit facilities including the New York City Subway system and the Port Authority’s own PATH trains connecting Manhattan to New Jersey.
One of the world’s largest gold depositories was stored underneath the World Trade Center, owned by a group of commercial banks. The 1993 bombing detonated close to the vault. Seven weeks after the September 11 attacks, $230 million in precious metals was removed from basement vaults of 4 WTC, which included 3,800 100-Troy-ounce 24 carat gold bars and 30,000 1,000-ounce silver bars.
February 13, 1975, fire:
On February 13, 1975, a three-alarm fire broke out on the 11th floor of the North Tower. Fire spread through the tower to the 9th and 14th floors by igniting the insulation of telephone cables in a utility shaft that ran vertically between floors. Areas at the furthest extent of the fire were extinguished almost immediately and the original fire was put out in a few hours. Most of the damage was concentrated on the 11th floor, fueled by cabinets filled with paper, alcohol-based fluid for office machines, and other office equipment. Fireproofing protected the steel and there was no structural damage to the tower. In addition to damage caused by the fire on the 9th – 14th floors, water from the extinguishing of the fires damaged a few floors below. At that time, the World Trade Center had no fire sprinkler systems.
February 26, 1993, bombing:
The first terrorist attack on the World Trade Center occurred on February 26, 1993, at 12:17 p.m. A Ryder truck filled with 1,500 pounds (680 kg) of explosives, planted by Ramzi Yousef, detonated in the underground garage of the North Tower. The blast opened a 100 foot (30 m) hole through five sublevels with the greatest damage occurring on levels B1 and B2 and significant structural damage on level B3. Six people were killed and 1,042 others were injured during escape attempts complicated by smoke infiltration from the base of the building up to the 93rd floor of both towers. Many people inside the North Tower were forced to walk down darkened stairwells that contained no emergency lighting, some taking two hours or more to reach safety.
Yousef fled to Pakistan after the bombing but was arrested in Islamabad in February 1995, and was extradited back to the United States to face trial. Sheikh Omar Abdel Rahman was convicted in 1996 for involvement in the bombing and other plots. Yousef and Eyad Ismoil were convicted in November 1997 for their carrying out the bombing. Four others had been convicted in May 1994 for their involvement in the 1993 bombing. According to a presiding judge, the conspirators’ chief aim at the time of the attack was to destabilize the north tower and send it crashing into the south tower, toppling both landmarks.
Following the bombing, floors that were blown out needed to be repaired to restore the structural support they provided to columns. The slurry wall was in peril following the bombing and loss of the floor slabs that provided lateral support against pressure from Hudson River water on the other side. The refrigeration plant on sublevel B5, which provided air conditioning to the entire World Trade Center complex, was heavily damaged. After the bombing, the Port Authority installed photoluminescent markings in the stairwells. The fire alarm system for the entire complex needed to be replaced because critical wiring and signaling in the original system was destroyed. As a memorial to the victims of the bombing of the tower, a reflecting pool was installed with the names of those who had been killed in the blast. However, the memorial was destroyed following the September 11 attacks. Names of the victims of the 1993 bombing are included in the National September 11 Memorial & Museum.
January 14, 1998, robbery:
In January 1998, Mafia member Ralph Guarino, who had gained maintenance access to the World Trade Center, arranged a three-man crew for a heist that netted over $2 million from a Brinks delivery to the eleventh floor of the World Trade Center.
In 1974, French high wire acrobatic performer Philippe Petit walked between the towers on a tightrope, as shown in the documentary film Man on Wire (2008), based on Petit’s book To Reach the Clouds: My High Wire Walk Between the Twin Towers (2002) (released in paperback with the title Man on Wire (2008) and depicted in the feature film The Walk (2015). Petit walked between the towers eight times on a steel cable.
In 1977, Brooklyn toymaker George Willig scaled the exterior of the South Tower (2 WTC).
In 1983, on Memorial Day, high-rise firefighting and rescue advocate Dan Goodwin successfully climbed the outside of the North Tower (1 WTC). His stunt was meant to call attention to the inability to rescue people potentially trapped in the upper floors of skyscrapers.
The 1995 PCA world chess championship was played on the 107th floor of the South Tower.
In 1998, the Port Authority approved plans to privatize the World Trade Center. In 2001, the Port Authority sought to lease the World Trade Center to a private entity. Bids for the lease came from Vornado Realty Trust, a joint bid between Brookfield Properties Corporation and Boston Properties, and a joint bid by Silverstein Properties and The Westfield Group. By privatizing the World Trade Center, it would be added to the city’s tax rolls and provide funds for other Port Authority projects. On February 15, 2001, the Port Authority announced that Vornado Realty Trust had won the lease for the World Trade Center, paying $3.25 billion for the 99-year lease. Vornado outbid Silverstein by $600 million though Silverstein upped his offer to $3.22 billion. However, Vornado insisted on last minute changes to the deal, including a shorter 39-year lease, which the Port Authority considered nonnegotiable. Vornado later withdrew and Silverstein’s bid for the lease to the World Trade Center was accepted on April 26, 2001, and closed on July 24, 2001.
August 25, 1966
1 WTC: August 1968
2 WTC: January 1969
3 WTC: December 1979
4, 5, and 6 WTC: 1970
7 WTC: 1983
1 WTC: December 23, 1970
2 WTC: July 19, 1971
3 WTC: July 1981
4, 5, and 6 WTC: 1975
7 WTC: May 1987
April 4, 1973
1 WTC: 1,730 feet (530 m)
1 WTC: 1,368 feet (417 m)
2 WTC: 1,362 feet (415 m)
3 WTC: 250 feet (76 m)
4 and 5 WTC: 120 feet (37 m)
6 WTC: 110 feet (34 m)
7 WTC: 610 feet (190 m)
1 WTC: 1,350 feet (410 m)
2 WTC: 1,350 feet (410 m)
1 and 2 WTC: 110 floors
3 WTC: 22 floors
4 and 5 WTC: 9 floors
6 WTC: 8 floors
7 WTC: 47 floors
1 and 2 WTC: 4,300,000 sq ft (400,000 m2) each
4, 5, and 6 WTC: 500,000 sq ft (50,000 m2) each
7 WTC: 1,868,000 sq ft (170,000 m2)
1 and 2 WTC: 99 each