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The concept for the new design was to create a parallelogram in plan, extruded into a 60-story-high crystal prism. The base volume grounds the single extruded parallelogram and supports the tower visually. SOM proposed locking the base and tower with a third interior volume of light, the shape of which becomes most apparent at night.

We sought to embed light in all of the building's levels. From the podium to the special linear-lap curtain wall, light appears to emanate from the building itself. Our contribution to the design included glass panels that overlap the building's floor plates and a spandrel system that reflects light from behind the panels, creating a luminous tower that extends light into the public realm.

Process

With the design of 7 World Trade Center, each part of the building had a very specific role, and the design evolved within a specific context. David Childs, who has been a very supportive collaborator on many of our projects, brought us in to participate on this project early on.

At the time, there wasn't a complete idea about the tower, but SOM knew they wanted a solid base, defined by the transformers contained there, and that the base would somehow merge with the tower. They were looking at different conceptual ideas, such as a slinky, where the metal base would be very dense and get thinner and thinner as it stretched up the building.

The broadest influence we brought to the project was to conceive the overall building as a structure that would be able to respond luminously to its immediate environment. Both the local urban conditions and the particular quality of downtown light would be the organizing principle of the design.

Luminous Result

From that point on, we worked on the principle of a volume of light, where the glass curtain wall would act as a reflector and a subtle reimaging device for its surroundings. When you look at the finished building, you're made more aware of the quality of light happening at that moment.

We did this both with an unconventional curtain wall and a unique skin for the base of the building. Instead of having the curtain wall interrupted at the floor plates, we allowed the glass unit to pass over the floor edge and terminate at the midpoint of the recessed spandrel, thereby defining the floors by revealing a void.

Below the resulting floating portion of the insulated glazing unit (IGU), a reveal allows light to be inserted behind the curtain wall by means of a formed spandrel section. The spandrel section consists of an inclined blue reflector at the sill that reflects daylight up onto a vertically curved, specular metal panel, which in turn projects the light out and down through the backside of the floating section of the IGU. The result is that the tower's structure is embedded with light and merges with the sky.

Beyond transparency, our projects strive to make people aware of nature and to reveal nature's presence, despite our assumption that we are divorced from it. We conceive of ways to re-establish these connections, which inevitably are there but often overlooked. We understand glass as having the means to do this.

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James Carpenter, architect and sculptor, practices architectural design and structural glass design with his firm, James Carpenter Design Associates. Their work includes projects at Hearst Tower in New York City and Sweeney Chapel at the Christian Theological Seminary in Indianapolis, among others. Carpenter received a MacArthur Foundation Fellowship in 2004.

Jeannie Kim is the publications editor at Columbia University's Graduate School of Architecture, Planning and Preservation, where she also teaches.

This article is excerpted from Engineered Transparency, edited by Michael Bell and Jeannie Kim, copyright © 2009, with permission of the publisher, Princeton Architectural Press.

SUBSCRIPTION SAMPLE Seven World Trade Center's curtain wall employs a low-iron glass with a reflective coating. Photo: David Sundberg Extra Large Image The ability of the 7 World Trade Center curtain wall to both reflect and transmit light produces a highly variable facade. Photo: David Sundberg Extra Large Image The overlapping spandrel panel detail of 7 WTC's curtain wall was mocked-up by the architects. Photo: Courtesy James Carpenter Design Associates Extra Large Image Diagram showing the predicted winter and summer daylight interactions with the curtain wall, at the spandrel panel. Image: James Carpenter Design Associates Extra Large Image Exploded axonometric drawing of 7 World Trade Center's curtain wall. Image: James Carpenter Design Associates Extra Large Image Detail section drawing at the spandrel panel of the 7 WTC facade. Image: James Carpenter Design Associates Extra Large Image The partially reflective glass cladding of 7 World Trade Center allows the building to mirror its surroundings under certain conditions. Photo: Andreas Keller Extra Large Image Engineered Transparency, edited by Michael Bell and Jeannie Kim. Image: Princeton Architectural Press Extra Large Image   Click on thumbnail images to view full-size pictures.