The designed for the final World Trade Center tower were revealed last month, marking a major milestone for the 16-acre complex, but there is good reason why tower no. 2 is the final one. Yes, funding and future tenants played a part, but Capital New York reports that the bigger issue is that the site itself is extremely complicated. Why? There is a giant ventilation system on the property that can not be moved and it must remain operational. It circulates air for the transit hub and underground stairwells, and 2 World Trade Center needs to be constructed around it. Bjarke Ingels, the new architect for the tower, told Capital, "I think you probably couldn't find a more difficult place in the world to build a 1,300-foot tower."

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Capital says, "to keep the ventilation system online, Ingels' team has been asked to figure out how to 'weave' the building's support columns through all the machinery."

Construction crews will have to assemble the first three floors without disturbing the equipment. Then they must "duplicate" all of it; that is to say, they will build a replica of the machinery inside the tower. New air pipes will be snaked up the building. Then, somehow, the systems will be switched over without severely disrupting PATH train service or the underground retail shops. "The machinery has to keep running to keep the hub alive," Ingels said. "Duplicate the machinery, switch it on, and then we can start clearing the ground floor for our purposes. So, baked into the site is already a few additional challenges, above and beyond the programmatic and sort of gravity requirements."

Have fun with that! For what it's worth, developer Silverstein Properties and other building experts don't foresee any issues.

· For final World Trade tower, a construction obstacle course [Capital]

· The Final World Trade Center Tower's New Design, Revealed! [Curbed]

