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ETFE membrane installed in North America

Awnings & Canopies, Markets, Projects | June 1, 2009 | By:

A North American first shelters shoppers and diners in “Kansas City’s living room.”

When sprinter Muna Lee ran in the 200-meter finals at the Beijing Olympics, she competed beneath the same membrane that she may have dined under in her home town of Kansas City, Missouri. The single-layer ethylene tetrafluorethylene (ETFE) membrane, which is relatively new in architectural use, is an integral part of Beijing’s National Stadium roof—and for the canopy above an atrium at the new KC Live! entertainment complex. And while Lee didn’t set a record, the KC Live! canopy did: It’s the first single-layer ETFE membrane system installed in North America.

The membrane canopy was proposed, and eventually installed, by the Kansas City-based Structurflex LLC, which is partly owned by Structurflex in Auckland, New Zealand. It wasn’t coincidence that the local company won the bid, says Bart Dreiling, president of North and South American operations at Structurflex. It was good networking and a winning proposal.

Going membrane

By chance, Dreiling met an architect from the project’s firm at a dinner party. The architect explained the design concept, the desire to make the courtyard a focal point, and the need for a covering to protect customers from rain, provide shading and define the space.

KC Live! is part of a nine-block, $275 million mixed-use revitalization project in downtown Kansas City called the Power and Light District. The KC Live! complex, which is all-new construction, encompasses one square block with a two-and-a-half-story building that surrounds a large central courtyard. Tenants of KC Live! include restaurants, bars and a bowling center. The courtyard is used for dining, as a concert venue and for viewing sporting events on its large-screen monitor. Its marketing tag: “Kansas City’s Living Room.”

Dreiling responded with three formal proposals: one with PTFE, one with PVC, and one with single-layer ETFE.

In the end, ETFE became the clear choice. Glass, the original preferred material, exceeded the budget. Steel was too heavy, and didn’t give the desired open-air feel. The project’s developer, Baltimore, Md.-based The Cordish Companies, was familiar with fabric structure technology and was intrigued with the possibility of breaking ground with a new material, Dreiling says.

ETFE’s other selling points included its transparency, its modern look and its price tag. The final cost was less than $1.8 million, which was about half the cost of a glass structure.

The stretch

Dreiling proposed a turnkey operation for the developer, which included design, engineering, the materials and the entire installation. Structurflex worked in conjunction with German supplier covertex GmbH (owned by Germany-based Seele Group) for the design, the ETFE fabrication and for installation assistance. The ETFE was manufactured by Nowofol GmbH, also in Germany.

The design and engineering process took about three months, which included detailed specifications of the external structure and trusses. Fabrication and shipping took another three-plus months. The sheets of ETFE were made-to-order based on the structure measurements, with little opportunity for alteration; since the membrane is stretched to fit, the design and engineering needed to fit into the membrane’s elastic range.

The ETFE received a special treatment in production. A silver fritted reverse dot print was added to the membrane, primarily to provide a level of shading, which also gives 75 percent translucency to allow the surrounding downtown skyline to be seen through the cover. Its secondary purpose was for nighttime light effects. During concerts or other after-dark events, the membrane can act as a colorful backdrop by reflecting lights from a sophisticated LED system installed on the underside of the steel.

Extreme installation

The most difficult part of the project was the installation of the truss framework. Permits were needed to partially close city streets on either side of the development, and cranes were called in for heavy lifting. The steel installation took nearly a week. “We had to erect [the trusses] over the top of a two-and-a-half-story building,” Dreiling says. “The total reach was about 175 feet and each half-truss weighed about 11,000 pounds. Trying to lift them over the top of the buildings was challenging. Making the three connections was also a challenge.”

Once the trusses were in place, an international team of experts and a local crew took about six weeks to install the membrane. On any given day, there were four to 10 people working on the installation. The panels were unrolled and 27 tensioning cables, ranging from 5/16 to 7/8 inch in diameter, were pulled through channels in each panel. The panels were then lifted onto the steel structure and pulled to the correct tension by the cables. The canopy has a total of 336 cables providing support and tension. Because ETFE is extremely lightweight—1 percent of the weight of glass—the cables also determine the overall load the canopy can bear.

While the installation was generally smooth, Structurflex staff also learned things that they would do differently next time, Dreiling says. “Small things to speed up the installation and ways to make connections simpler … It was a much more delicate process than typical fabric because ETFE is nonwoven; it’s extruded. It can get punctures or tears a lot easier than fabric. It’s a lot riskier.”

Punctures can be patched with an adhesive-backed film, adds Dreiling. Also, if the material is punctured while under tension, it’s unlikely that a larger tear or rip would ensue. “One of the key attributes of ETFE foil is that it has a very low tear propagation,” he says. This is one of the advantages it has over fabric, which has a scrim made up of small fibers and strands that can sometimes have high tear propagation properties.

Although sharp objects are therefore not welcome nearby, the membrane is strong. It can withstand the weight of a human walking, will hold up under heavy snowfall, and does not degrade from sun, cold or other outdoor elements for up to 30 years.

Everything’s up to date

The project, completed in December 2007, is a point of pride for Structurflex. “It cemented our position as a leader in the membrane structure industry,” Dreiling says. “Furthermore, with it being in our back yard, where we are surrounded by the largest sports and events facility design firms in the world, it was even more important to get it right.”

When new clients or corporate visitors come to town, Dreiling makes sure that KC Live! is one of their first stops. “Rather than just a presentation with wonderful pictures, we now have a 27,000-square-foot project that we can easily reference when speaking to one of the most important architectural communities in the United States,” he says.

Although that architectural community was skeptical at first, the project has been well accepted, and shows architects, designers and contractors that this can be a smart, efficient alternative to glass or other systems. Since KC Live!, Structurflex has worked on additional projects using the single-layer ETFE membrane. It’s also something that the KC Live! project developer said would be considered for future projects.

Dreiling can also speak to the project’s success on a more personal level. “When it first opened, I went down there a little too much and got in trouble with my wife,” he says. “It’s a really good time there, and it’s the newest hot spot in Kansas City.”

Lynn Keillor is a writer and editor based in Minneapolis, Minn.

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