​Half-Pint Prototype: The Outsize Influence of 7 World Trade Center

By Judith Dupré

This post is excerpted from One World Trade Center: Biography of a Building (Little, Brown & Co., 2016).

Design, safety features, and construction methods developed for 7 WTC (right) influenced those of One WTC (left). Photo: DBOX/Little, Brown and Company

Design, safety features, and construction methods developed for 7 WTC (right) influenced those of One WTC (left). Photo: DBOX/Little, Brown and Company

To fully appreciate One World Trade Center, one must begin at Seven World Trade Center, simply called Seven. Completed in 2006, Seven was the first tower to be rebuilt after September 11. Its construction was catalytic, refocusing prolonged discussions from what should be done at the World Trade Center to actually getting it rebuilt. Seven’s design, safety measures, and civic generosity established a benchmark that set the tone for the rest of the World Trade Center site.

Its innovations would be incorporated into every subsequent Trade Center tower — and towers built around the globe. Designed by Skidmore, Owings & Merrill (SOM), engineered by WSP | Parsons Brinckerhoff and Jaros Baum & Bolles, built by Tishman/AECOM, and developed by Silverstein Properties, Seven also saw the creation of a team of experts, all of whom would go on to work on One World Trade Center, bringing their skills and close working relationships to that project.

7 WTC’s unique curtain wall design gathers light and redirects it, illuminating the streets. Photo: DBOX/Little, Brown and Company

7 WTC’s unique curtain wall design gathers light and redirects it, illuminating the streets. Photo: DBOX/Little, Brown and Company

Routinely appraised as one of the finest new skyscrapers in Manhattan, Seven is a 42-story tower, sheathed in transparent glass, whose appearance changes over the course of the day according to the quantity and quality of available light. Its prismatic façade was created in collaboration with James Carpenter Design Associates, a firm known for pushing the aesthetic and environmental boundaries of building envelopes. “One of the great attributes of New York is the quality of light we have here, specifically, downtown,” Carpenter said. “Because we’re between two rivers, there’s a lot of moisture in the air. Tiny spheres of water that are in the air make the light, endow it with a physical presence.” While the atmospheric conditions downtown are laden with potential, its narrow streets tend to be dark. To counter this, the curtain wall was designed to gather natural and ambient light from adjacent buildings and redirect it, illuminating the streets.

“We had to do something to show the world that was busy migrating out of lower Manhattan that we were going to rebuild lower Manhattan... I said, ‘Let’s get this rebuilt. Let’s start the design.’ And that’s exactly what I did.” —- Larry Silverstein

SOM developed 7 WTC’s cable-net glass entrance with James Carpenter and Schlaich Bergermann, a safety feature also used at One WTC. On the left is the blast-resistant wall that is an integral part of the Holzer/Carpenter art installation. Photo: Joe Woolhead/Silverstein Properties

SOM developed 7 WTC’s cable-net glass entrance with James Carpenter and Schlaich Bergermann, a safety feature also used at One WTC. On the left is the blast-resistant wall that is an integral part of the Holzer/Carpenter art installation. Photo: Joe Woolhead/Silverstein Properties

Without the microscopic scrutiny that delayed construction of the adjacent sixteen acres, Seven was built quickly, despite complex structural issues. The building was an audition of sorts — for SOM, but to a far greater extent for Larry Silverstein. Although he had built the original Seven World Trade Center, the eyes of the world were on him this time around. “The subtext of everything was that the state could come in and buy him out in a minute.... They were never going to pull that trigger, but he had to show that he was going to be a responsible developer, that he was building a good building,” said architect Kenneth A. Lewis of SOM.

A parallelogram in plan, Seven’s elegant profile was shaped by the restoration of Greenwich Street, a civic gesture that indicated that Silverstein wanted the new Trade Center to be as much about lively public spaces as it was about quality architecture. However, the new design required building a smaller tower and forfeiting leasable square footage. Geoff Wharton, who at the time led Silverstein’s efforts at the World Trade Center, convinced his boss, saying, “Larry, we’ve got thirteen other acres that we can put all that unused FAR [floor area ratio] onto. We don’t have to use it on this site, let’s do what’s right for [Seven],” David Childs recalled. Silverstein made Seven taller and narrower than its predecessor, and lost about 300,000 square feet (27,871 m2) in the process.

Seven’s base made unique demands. It had to accommodate a new ConEd substation, after the one housed inside the original Seven World Trade Center was destroyed. The replacement substation contained massive transformers, each weighing about 250,000 pounds (113,398.1 kg) and measuring nearly eighty feet (24.4 m) tall. To reestablish a sidewalk entrance (the previous entrance had been elevated), Seven had to be built around these transformers. Complicating matters further, the transformers had to be ventilated and above grade; they couldn’t be lowered into the ground because the land is infill, reclaimed years ago from the Hudson River.

These requirements determined the design of Seven’s eighty-two-foot-high (25 m) podium wall, which is sheathed in a double stainless-steel skin with a seven-inch (17.8 cm) internal cavity that permits uninterrupted airflow. The skin’s stainless steel panels are variously angled to catch light, visually complementing the upper crystalline tower. Because the substation precluded putting shops and restaurants on the ground level, the podium scrim was fitted with LED fixtures that cast patterned blue and white light at night. To further animate the lower walls, motion sensors track movement on the sidewalk, displaying vertical bars of colored light as pedestrians walk by. When the new substation opened in May 2004, the beginnings of the new Seven, then about twenty feet (6.1 m) high, rose above it.

Landscape architect Ken Smith designed the triangular park in front of 7 WTC, formed by the intersection of Greenwich Street and West Broadway. Jeff Koons’ whimsical Balloon Flower (Red) sculpture is its centerpiece. Photo: Joe Woolhead/Silverstein Properties

Landscape architect Ken Smith designed the triangular park in front of 7 WTC, formed by the intersection of Greenwich Street and West Broadway. Jeff Koons’ whimsical Balloon Flower (Red) sculpture is its centerpiece. Photo: Joe Woolhead/Silverstein Properties

Seven’s entrance appears remarkably open and light, yet deploys a three-tiered security strategy. The entrance’s cable-net glass wall brings in light but is blast-resistant. Inside the lobby, a protective illuminated ceiling changes in luminosity and color during the day (white) and at night (blue). A glass wall behind the reception desk is actually a cleverly disguised blast shield that protects the elevator lobbies. It is also a work of art: For 7 World Trade is a 2006 installation by artist Jenny Holzer, made in collaboration with Carpenter, which features scrolling snippets of poetry and prose about Manhattan. Carpenter designed the wall, which consists of two layers of glass, between which is suspended the LED system that generates the literary texts. More than a site-specific work, the piece marks the first time artists collaborated on the structural design of a building.

With input from others, Seven’s architects and engineers developed safety and security solutions that formed the basis of future high-rise building codes. At the time it was designed, the New York City Building Code, not updated since 1986, was prescriptive. After September 11, the New York City Building Department rewrote the code, although changes governing security and safety would not be incorporated until 2008.

Seven’s safety measures largely established — and exceeded — the new code. Its stairwells, twenty percent wider than required, are pressurized and marked with glow-in-the-dark strips so tenants can exit easily and quickly during an evacuation. Leaky coaxial wiring for walkie-talkies allows uninterrupted emergency communications. Enhanced fireproofing material coats columns and floors. Critically, the central concrete core, two feet (0.6 m) thick and running the tower’s full height, contains and protects stairways, elevators, communication systems, water storage, and power sources.

The skyscraper boasts equally impressive environmental features. It was the first building in Manhattan to receive Gold LEED certification from the U.S. Green Building Council. Its energy efficiencies include full-length glass windows that maximize daylight, high- performance HVAC and plumbing systems, and rooftop rainwater collection. Even the tenant leases are green: In 2011, Seven’s leases became the first to incorporate groundbreaking language that allows owners and tenants to share the costs and benefits of sustainable improvements. The tower was fully leased by 2011.


Judith Dupré has written several works of illustrated nonfiction about architecture. She is a 2015 National Endowment for the Humanities Public Scholar. For more information, visit OneWTCBook.


Notes

“One of the great attributes”: James Carpenter, James Carpenter Design Associates, interview, May 13, 2014.
“We had to do something”: Larry Silverstein, Chairman, Silverstein Properties, interview, Apr. 10, 2014.
“The subtext of everything”: Kenneth A. Lewis, Managing Director, SOM, interview, Apr. 11, 2014.
“Larry, we’ve got thirteen”: David M. Childs, Chairman Emeritus and Consulting Design Partner, SOM, interview, Mar. 13, 2014.
“For 7 World Trade”: Holzer’s installation scrolls quotations about Manhattan in a loop that is about thirty-six hours long. It includes lines from American poets, such as Elizabeth Bishop, Langston Hughes, Walt Whitman, and William Carlos Williams, and from songwriter Woody Guthrie and essayist E. B. White. When the installation is viewed at an angle, the wall’s acid-etched surface causes the text to transform into a luminous volume of white light.
“safety measures largely established”: T.J. Gottesdiener, Managing Partner, SOM, interview, Mar. 13, 2014.