Construction of One World Trade Center

One World Trade Center is the main building of the rebuilt World Trade Center complex in Lower Manhattan, New York City. After the old World Trade Center was destroyed, plans for a new building took time because of disagreements between the Port Authority of New York and New Jersey and the developer.

Construction started in 2006, with Tishman Realty & Construction chosen to build it. The building reached ground level on May 17, 2008, and after many years of work, it was finished on May 10, 2013.

The new One World Trade Center opened to tenants on November 3, 2014. Later, on May 29, 2015, the One World Observatory opened to the public, offering great views of the city.

2004–2007

One World Trade Center was the first big building to use a special 3D plan for its design. A special ceremony to start building happened on July 4, 2004, but building didn’t start right away until 2006. The delay was because of arguments about money and safety. These problems were fixed in April 2006 with an agreement between the builder Larry Silverstein and the Port Authority of New York and New Jersey.

In the summer of 2006, safe explosions cleared the ground for the building’s base. In November 2006, a large amount of concrete was poured into the foundation. In December 2006, people signed a big steel beam, which was then added to the bottom of the building.

In early 2007, more beams were added on top of the first ones. That year, plans said the building would cost about $3 billion. Money from insurance and loans helped pay for it. By the end of 2007, the building’s foundations were almost finished, and work continued on putting up the structure.

2008

In January 2008, two construction cranes arrived at the construction site. The tower’s strong center, called the concrete core, began to grow in early 2008. By February 22, 2008, 9,400 short tons of steel had been ordered. That was about one-fifth of the steel needed.

In March, the steel for the tower reached 70 feet high, but it was still below street level.

From late March to early April, a 40-foot tall model of a wall section with twenty-four windows was tested in Ontario, California, and another model was tested south of Albuquerque, New Mexico. The tests checked if the all-glass exterior could stay strong during earthquakes and very bad weather, and both models passed. In mid-April, a batch of concrete had to be replaced because it failed a test.

On May 17, 2008, the tower’s steel reached street level as new sections were added to two of the twenty-four large steel columns marking the building’s footprint. In June, the steel skeleton of the tower’s concrete base started to take shape, and concrete was poured for the floor of the tower’s basement level B3. By the end of June, about 90 percent of the construction contracts had been bid.

By August, 1 WTC had reached 25 feet above street level. In September, the Port Authority board approved contracts for security and building management systems, and 95% of the contracts needed to finish the tower had been signed. On October 10, more concrete was poured for the tower’s concrete core, raising it just above street level.

2009

By February 11, 2009, the tower reached 105 feet (32 m) above street level. On July 2, 2009, builders poured a lot of concrete to help make the area near the street.

On August 13, they placed a huge piece of steel — the largest column put in so far. Each steel column came from a factory and was about 60 feet (18 m) long. By November 1, 2009, all the outer columns of the tower were up, and work on the second floor was almost finished.

2010

In 2010, workers kept building One World Trade Center. They finished the fifth floor in January and started on the sixth floor in February. By the end of March, they began putting up steel beams for the second office floor. In April, they added a special shape to the building and completed the base with concrete.

In May, builders were adding about one floor each week and planned to finish 55 stories by the end of the year. They also added a new safety system to the steel structure, the first of its kind in the city.

In July, workers found pieces of an old ship from the 1700s while digging for an underground area. They discovered part of the ship's hull and an anchor. The ship was probably used long ago to help build up the land in Manhattan.

By October, the building had reached 44 stories. In November, they started putting on the glass outer walls, beginning on the 20th floor. By December, the building had grown to 52 stories and was higher than 600 feet, halfway done with its steel frame.

2011

By February 2011, the tower had reached 56 floors and was 667 feet tall. The glass panels had reached up to the 27th floor. On May 12, 2011, plans to add special glass to the base of the building were stopped because of technical issues.

By June 15, 2011, One World Trade Center had reached the 70th floor. The glass on the outside had reached the 45th floor, and concrete floors had been built up to the 63rd floor. On August 1, 2011, some workers stopped working for a short time because their work agreement had ended. They started working again on August 3.

2012

In early 2012, work on One World Trade Center slowed because of cold weather and wind. There were also delays getting steel from a supplier. By March, the weather got better and work continued above the 92nd floor. In May, there was a plan to change the top of the building, but this idea was later changed back.

In June 2012, the building reached its highest roof level and was around the 30th tallest skyscraper in the world. Hot weather caused more delays, but by July, workers started putting up the top parts of the building. A special beam signed by the U.S. President Barack Obama and others was placed on August 2, 2012.

By August 30, 2012, the main structure of the building was finished. In the next few months, workers got ready to add a very tall spire to the top of the building. The spire was made in pieces in a factory near Montreal, Quebec, Canada, and brought to New York City. In December 2012, the first pieces of the spire were lifted to the top of the building.

2013–2015

On May 10, 2013, the last two pieces of the building's tallest point were put in place. This made it the tallest building in the Western Hemisphere and the third tallest in the world.

Work on the outside of the building finished in June 2014. The inside was done by November that same year. The building opened on November 3, 2014, for some workers. Later, on May 29, 2015, the observation area at the top opened for everyone to visit.