NEW YORK -- Eager to avoid creating a fortress that overshadows the World Trade Center memorial, the architects of the Freedom Tower unveiled a new approach yesterday: They would wrap its 187-foot-high, bomb-resistant concrete base in a screen of glass prisms rather than metal panels.
This and other refinements were described by the lead architect, David M. Childs of Skidmore, Owings & Merrill. He spoke at an awards ceremony held by the New York chapter of the American Institute of Architects in 7 World Trade Center, overlooking the Freedom Tower site, which is under excavation.
Even after the revisions, the building would still evoke the twin towers in its height and proportions. Its rooftop parapet would be 1,368 feet above the street, as was that of 1 World Trade Center, the north tower.
If all goes according to plan, the 2.6 million-square-foot Freedom Tower would be open in 2011.
In the first redesign last year, the base of the tower was to have risen 200 feet and perhaps be clad in stainless steel, aluminum or titanium. Though Childs envisioned these panels as enlivening the almost windowless facade, others despaired about its monolithic quality. The phrase "concrete bunker" was tossed around.
"There were a lot of concerns that this was going to look like a fortress," said Kenneth J. Ringler Jr., the executive director of the Port Authority of New York and New Jersey, for which Silverstein Properties is developing the Freedom Tower.
The basic form of the building has not changed. It is an obelisk on which the corners are both tapered and chamfered, or cut away diagonally. The tip of its spire would still mark the symbolic pinnacle of 1,776 feet. It would be illuminated at night in an echo, however abstract, of the Statue of Liberty's torch.
And, barring new competitors, it would be the tallest building in the United States.
In the redesign last year, the tower was given a smaller floor area, or footprint, increasing its distance from West Street-Route 9A and any bomb-laden vehicle that might approach along that highway. With smaller floors, Childs said, it was no longer practical or desirable to have as many elevator shafts running the full height of the building, dictating a transfer floor, an unexceptional feature of high-rise buildings.
Although the idea summons memories of the 78th-floor sky lobby in 2 World Trade Center, where many people died Sept. 11 as they waited for express elevators, "Sky lobbies are almost inevitable in these tall skyscrapers," said Glenn P. Corbett, an assistant professor of fire science at John Jay College of Criminal Justice.
There would be five service elevators that could reach every floor, including one water-resistant car, housed in a protected shaft, for use by firefighters and other rescue workers in an emergency. The biggest changes have been made to the base, in essence, a security pedestal that is meant to lift the glass-clad office tower out of harm's way in case of a bombing.
Though it looks fairly small in an overall view of the building, the base would dominate almost any view north from the World Trade Center memorial, across Fulton Street. The only occupied space within the base would be the lobby, with 50-foot ceilings.
Childs said that full-scale mock-ups of the prism wall will be built in Kearny, N.J., to ensure that the fractured, reflected sunlight will not blind pedestrians or drivers.