World Trade Center Tower 4

Cost: $2 billion

The progress since the start of construction last spring on the 64-story World Trade Center Tower 4 is a success story on a multi-mega-project program rife with delays, lawsuits and political turmoil that has caused public anger and devastation since the 16-acre site of the Sept. 11 attacks started undergoing redevelopment.

The 975-ft office tower at 150 Greenwich Street, which will face the World Trade Center memorial and the Freedom Tower, will be the fourth tallest skyscraper in the U.S. and the first U.S. office building designed by Pritzker-Prize winner Fumihiko Maki, who clad the concrete-and-steel building with a signature "minimalist" 757,000-sq-ft curtain wall.

Its construction has been anything but minimalist or simple, however.

It took the Port Authority of New York and New Jersey two years to excavate the proposed site, and the process was not without surprises: excavators came across a large pit formed by an advancing glacier in the 40- to 60-ton bedrock necessary to support the weight of the future tower. The team had to first fill it with high-grade concrete, bringing the total amount of required concrete to 114,000 cubic yards (as well as 22,100 tons of steel). The nearby subway line tracks required the Port Authority to put up a retaining wall on the western side of the construction site; its mere existence caused some to say the site was not ready and resulted in arbitration that had the agency--who will lease one-third to two-thirds of the building's office space from Silverstein upon completion in 2012--owing $50 million to the site’s developer, Silverstein Properties, for delays.

Nonetheless, issues resolved, the $2 billion project (originally estimated at a little over $1 billion) is now underway, with the team, headed by New York's Tishman Construction, figuring out ways to meet the deadline.

"In order to maximize the construction schedule, the below-grade work is being done in a tiered or wedding cake fashion," Malcolm Williams, assistant construction manager at Silverstein wrote in an e-mail reply to questions about the project. "As opposed to completing one entire level at a time, one area may have several areas that are two or three levels ahead of areas in a different section of the below-grade work."

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The first three floors, as well as two levels below grade, are reserved for retail podium. Above it, 44,000-sq-ft floor plates will reach to the 46th floor, after which the floor plates turn into 34,000-sq-ft trapezoids. Two elevator banks of eight cars each and one bank with six will serve the lower floors, with the upper floors serviced by two banks of six cards each, a central core running through both types of floor plans. A 45-foot span on the west side will face the memorial, while the 35-ft-span will face east. The building will also provide access to the below-grade transportation and retail concourse connecting to the Santiago Calatrava-designed central PATH terminal, itself scaled back considerably from its original plans. With these connections, ongoing integration with the rest of the projects surrounding WTC 4 became integral.

"The most challenging part of the project is the coordination of constructing 1 of 7 mega projects in a 16-acre site," says Williams. "Knowing what’s happening with the neighboring projects is crucial to the success of all the projects."

Like the completed WTC 7, the tower will seek LEED Gold, through a 20-percent energy need reduction over the city's standards, as well as tapping into the site's proposed 4.8 mW of power generation from fuel cells.

Team Box

Site owner: Port Authority of New York and New Jersey
Owner (public): Empire State Development Corp. and Lower Manhattan Development Corp.
Owner/Developer: Silverstein Properties, New York
Construction Manager at Risk: Tishman Construction, New York
Architect: Maki Associates, Tokyo
Foundation: Yonkers Contracting Co, Yonkers, NY
Mechanical Engineer: Jaros Baum & Bolles, New York
Structural Engineer: Leslie E. Robertson Associates, New York