There can't be many tougher briefs than designing an elegant but capacious iconic tower with high rental floor space while pushing boundaries in safety and sustainability. But Rogers Stirk Habour + Partners (RSH) is confident it can deliver just that as it prepares to unveil the detailed design of its 71-storey tower at New York's Ground Zero, one year after being appointed by site developer Larry Silverstein in May 2006.
The tower is one of a cluster of five being built to replace the Twin Towers destroyed in 2001. Under Daniel Libeskind's masterplan, the five towers will start with the highest tower, the Freedom Tower, designed by Skidmore Owings & Merrill, and then step downwards.
Richard Rogers was one of three superstar architects, along with Norman Foster and Fumihiko Maki, appointed by Silverstein on the strength of their body of work – in Rogers' case, constructions such as the Lloyds Building in the City of London, the Pompidou Centre in Paris and, more recently, the Stirling Prize-winning Barajas Airport in Madrid.
"It was just a straight appointment – we were asked to put together a team immediately," says RSH director Richard Paul of appointing a designer for Tower 3 at 175 Greenwich Street, in the middle of the cluster.
For the last year the RSH team has worked with Toronto-based executive architect Adamson Associates under a punishing schedule, punctuated by detailed presentations made directly to Silverstein every three weeks. "Larry is an amazingly informed client and he is very, very involved in the detail of this project," adds Paul.
The result is a 71-storey building, whose foundations will be directly above the new Path railway station designed by Santiago Calatrava (see link). Work will start on site in January 2008.
The building will have two basement levels for parking and shopping. A podium building will contain the triple height lobby space for the office, three floors of shops, a double-height mechanical room and five trading floors. Above the podium there are five mechanical floors and 54 office floors. At its peak, four beacons will provide an iconic addition to the Manhattan skyline.
"Everyone likes halos, but we wanted to illuminate the top vertically," says Paul. "The light peters out into the sky. We felt that having a crown of light at the top had been done before."
The four beacons define a slender central tower that is the highest of three plains. To allay fears that a 2.8 million square foot building on such a sensitive site would look too monolithic, the tower is divided into three plains: with a 400m-high central station, a northern section that stops at level 63 and a southern section that stops at level 47.
The 47-storey southern plain will help open up views between the south facade of Tower 3 and the western facade of the Maki tower, which are just 20m apart. "It's a way of articulating the mass to break down the volume and to ensure it still looks like an elegant tower reaching for the sky," says Paul.
The interior shows it is possible to design an iconic structure that is also commercially driven. "Larry wanted completely column-free corners for the building; all the corners are hung from the structural elements and columns on the outside of the building, which means we can keep them column-free."
Meanwhile, the floor beams have long spans that cut down on columns within the space, making the floors easy to reconfigure for tenants who want to customise their own space.
TOWER 3 PROTECTION
An obvious consideration is making people feel completely safe, allowing them to get on with their everyday tasks.
"A lot of the emotion surrounding the WTC site relates to how the people inside the Twin Towers were not protected, and it became clear that whatever was put in its place needed to have a level of protection far beyond anything that had been done before," says Paul. "The new building is very safe because the structure is very legible."
Security was a primary consideration right from the start of the design process. The building has a robust central concrete core containing all the necessary elevators, escape stairs and services.
The building's mainly glazed facade, based on an aluminium curtain wall system, will also be criss-crossed with steel bracing, ensuring the foundations take much of the vertical load and adding 'redundancy' to the structural stability. "The crossbracing makes the structure very legible, which reassures people," adds Paul.
Tenants will also be reassured by the fact that the building will not use too much energy. In fact, it is hoped that it will be awarded LEED Gold status – the highest rating under the US certificate for environmental performance – for its energy-saving features such as the glazing system to maximise solar gain, the intelligent lighting controls that will turn themselves off when they are not needed and the mechanical plant within the building powered by low sulphur fuels.
Preserving the memory of those who died on 9/11 was another important consideration, particularly for the western facade of Tower 3, which looks onto the World Trade Center Memorial.
The retail spaces on the first three floors of Tower 3 will look onto the eastern elevation on Courtland Street, leaving this quiet space in the footprint of the old Twin Towers free from the surrounding hustle and bustle. "We need to be very reverential, so around the corporate lobby is a very serene and green environment," says Paul.
Peter Walker, the landscape architect involved in the development of the memorial, has also worked on the public spaces around Tower 3 to ensure they reflect the language of the memorial. The landscaping, paving, seating and lighting around the tower are all designed with this in mind.
Meanwhile, the triple-height lobby will have a 'cable net facade' of tensioned steel strands, which Paul likens to a tennis racket. "The strings on a tennis racket absorb pressure right to the edge and enable us to keep the structure as minimal as possible. The cable net will create a connection between the lobby and the public realm nearby and allow people to engage with the entrance to the building."
Paul says it has been a great experience working on such a highprofile scheme, with all the architects involved in the masterplan together in one office. "The eyes of the world are on this site and there are a huge number of interested parties," he says. "You might think it would be difficult with all these architectural egos working so closely together, but it has worked fantastically well."