Design and Construction

Work on foundations began in 1966. Construction began in 1968.

The foundation for each tower extended more than 70 feet below ground, resting on solid bedrock. More than 1.2 million cubic yards of earth and rock were excavated to make way for the World Trade Center. The excavated material was placed in the Hudson River to create 23.5 acres of land deeded to the City of New York. This landfill is now Battery Park City.

More than 200,000 tons of steel was used in the World Trade Center's construction. The 425,000 cubic yards of concrete used in building the World Trade Center is enough to build a 5-foot-wide sidewalk from New York City to Washington, D.C.

The steel inside the WTC could have made three more Brooklyn Bridges.

There were 43,600 windows in the Twin Towers with over 600,000 square feet of glass window area cleaned by automatic window washing machines traveling on stainless steel tracks.

Each tower had 110 stories and was around 1,360 feet tall. (The roof of WTC1 was 1,368 feet above concourse level, 6 feet taller than WTC2, and supported a 360-foot antenna.) Each floor was 50,000 square feet (approximately one square acre) with each internal wall measuring 206 feet in length.

The 360-foot television mast atop One World Trade Center supported 10 main television antennas, numerous auxiliary antennas and a master FM antenna.

The buildings had their own ZIP codes — 10047 and 10048.

Each tower contained three central stairwells, which ran essentially from top to bottom, and 99 elevators. The sky lobby express elevators were capable of carrying 55 people, with a 10,000-pound capacity. Express elevators traveled at speeds of up to 27 feet per second.

Stairwells A and C ran from the 110th floor to the raised mezzanine level of the lobby. Stairwell B ran from the 107th floor to level B6, six floors below ground, and was accessible from the West Street lobby level, which was one floor below the mezzanine.

All three stairwells ran essentially straight up and down, except for two deviations in stairwells A and C where the staircase jutted out toward the perimeter of the building. On the upper and lower boundaries of these deviations were transfer hallways contained within the stairwell proper.

Each hallway contained smoke doors to prevent smoke from rising from lower to upper portions of the building; they were kept closed but not locked. Doors leading from tenant space into the stairwells were never kept locked; reentry from the stairwells was generally possible on at least every fourth floor.