Volume 21, Issue 1 - January 2007

Seven World Trade Center:
Secure, Sustainable, Efficient and Beautiful

Seven World Trade Center, the first building to be replaced within the Ground Zero area, stands as a glittering glass crystal, as architects at Skidmore Owings and Merrill LLC (SOM) refused to design a bunker-like structure. At its core, the building houses arguably the most sophisticated network of security features in any skyscraper in the world, but the building’s glass façade was designed to inspire hope and re-birth. “This project demonstrates that buildings can be secure, sustainable, efficient and beautiful,” explains Carl Galioto, FAIA, and technical partner at SOM.

The architectural team was able to achieve an almost astounding number of design objectives, many relating to innovative uses of glass. It is the first New York City skyscraper to receive a LEED-CS Gold rating. The 52-story building has airy floor-to-ceiling windows from the 10th story up. It uses an innovative layered spandrel system that continually reflects light in different ways, causing the building to continually change in appearance as light conditions vary. Building occupants are flooded with natural light, but are protected from glare. Finally, the building had to live up to landmark status, given its historic importance in the rebuilding of Ground Zero. 

“Our challenge was to create a very flat, mildly reflective, sharp, crisp object,” states Galioto. “The specific glass make up needed to balance visible light transmission, exterior reflectance, solar heat gain, interior reflectance, interior glare and U-value.” 

Push to the Limit
“Glass performance was pushed to the limit on this project,” says Rick Voelker, vice president of technical services for glass supplier Viracon Inc. “The design of the curtainwall required glass to do the seemingly impossible.” Viracon collaborated with SOM and building envelope supplier Permasteelisa Cladding Technologies, Windsor, Conn., to identify a custom glazing solution. 
Originally, plans called for a traditional glass coating, but the design team eventually opted for a custom solution that helped the team achieve a variety of goals. “After much research, we used a new coating, VRE-59,” Voelker states. 

At the time plans were being finalized, New York City introduced a new energy code, which VRE-59 surpassed. The coating was paired with a custom warm-edge spacer system and silk screen. Together, these elements helped acquire points toward meeting the team’s goal of LEED-CS Gold rating. 

Viracon also provided a custom silk-screen pattern that was designed specifically to reduce glare in the building, which called for towering 12-foot ceilings. The gray ceramic frit is dense at the top, phasing out by eye-level. This provides the least noticeable screen from the exterior and significantly lessens interior glare, while allowing natural light to flow into the space. “With such an extraordinary amount of glass in the tower, the high level of glare control that was achieved was a significant accomplishment,” says Voelker. 

During certain times of the day, the edges of the building seem to disappear, creating a floating effect. Low-iron glass was selected to create the most transparent building envelope possible. A custom vision spandrel glass system overlaps a stainless steel spandrel panel to reflect light in varying ways. To further enhance the “floating” illusion, the team used a gray sealant instead of traditional black. The gray sealant “disappears” as the building is viewed from the street level. “We expect to see architects increase their use of gray sealants as the effect is quite stunning,” says Voelker. 

Typical glass make up included: 1 3/16 inch VRE15-59 Insulating Silkscreen consisting of low-iron glass with Solarscreen VRE-59 on the #2 surface and a custom Dot Silkscreen pattern with Viraspan V948 (medium gray) ceramic frit color on the #2 surface with a stainless steel air spacer (warm-edge technology) with gray silicone sealant with low-iron glass for the interior glass ply. 

Architects' Guide to Glass & Metal
©  Copyright 2007 Key Communications Inc. All rights reserved. 
No reproduction of any type without expressed written permission.