When DuPont invented Ethylene Tetrafluoroethylene (ETFE) as an insulation material for the aeronautics industry in the 1930s, certainly no one envisioned its transformation into a revolutionary architectural material. Nearly 50 years later, the Vector Foiltec Group used ETFE to construct a small cable structure in Germany, demonstrating the use of this material as an alternative to glass for all building types. The use of ETFE then spread throughout Europe as designers learned of its lightweight, flexible, durable and sustainable nature. ETFE resists solar degradation and chemicals in the environment and is also fire retardant.
ETFE construction was highly publicized by its use in the 2008 Summer Olympics. ETFE was used in the recognizable National Aquatics Center (the Water Cube), an aquatics center used for swimming events, and in the Beijing National Stadium, which won an Award of Excellence in the architectural structures category of the 2008 International Achievement Awards.
The first single-layer ETFE project ever executed in North America was designed by Structurflex in Kansas City, Mo., a world-leading design and build manufacturer specializing in the design and construction of custom tensioned membrane structures in PVC, PTFE and ETFE. KC Live! is a large, covered, central courtyard used for dining, as a concert venue and for viewing sporting events, and is a part of the nine-block, $265 million mixed-use revitalization project.
The primary function of the structure was to define the space, while providing protection from the elements. Bart Dreiling, president, North and South American Operations for Structurflex, says the long life, low tear propagation and light weight of ETFE made it an easy choice when compared with alternative materials. A silver frit was added to the membrane, which gives 75 percent translucency to allow the surrounding downtown skyline to be seen through the cover, while still providing shade. As a secondary purpose the membrane acts as a colorful backdrop by reflecting lights from an LED system, for nighttime light effects. Another huge bonus: the price was about half of what a glass structure would have been.
Dreiling, an ETFE expert, describes the two typical applications for ETFE. The first is a single-layer system, where a film of ETFE is stretched and supported with cables. This application is most often used for open-air environments and canopies, like KC Live! The second common ETFE application is in the form of pneumatic pillows or cushions. Two or three layers of ETFE are inflated with low pressure air to provide insulation and resist wind loads. This method of construction with ETFE is useful for fully enclosed structures, and often used for zoos, atriums and other humidity controlled environments.
Structurflex helped design an exhibit that would mimic the conditions of a small slice of a rain forest in South America at The Buffalo Zoo in upstate New York.
“For this exhibit ETFE cushions were a clear choice. They needed transparency, to keep the space warm, and it needed to be sealed from outside environment,” Dreiling said. “Another big advantage is the transparency allows animals to absorb Vitamin D from the sun — polycarbonate and glass systems tend to block the UV spectrum that allows mammals to absorb Vitamin D into their system and then their diets must be supplemented.”
Birdair, Inc. in Buffalo, N.Y., a leading specialty contractor of tensile structures, has been awarded the contract to provide a pneumatic roofing system for a new porte-cochere using ETFE at the Empire City Casino at Yonkers Raceway in Yonkers, N.Y.
Press materials describe the structure as an approximately 11,000-square-foot porte-cochere. ETFE will cover a steel lattice shell structure to create a dramatic sculptural entrance canopy.
“The entrance canopy for the Empire City Casino is a new and impressive approach to ordinary casino design with its modern look,” said David Capezzuto, director of business development for Birdair. “ETFE provides greater design capabilities than a conventional glass system.”
Factors taken into consideration for the material choice included longevity, since “the ETFE material can last over 20 years without losing its transparency or strength.” Also, due to its nonstick surface, “ETFE resists airborne pollutants, making it chemically resistant and naturally self-cleaning.”
Challenges to ETFE?
Though ETFE has been described as a “miracle material,” it does come with some drawbacks.
ETFE is not very soundproof and requires very precise installation techniques. “Typically with membrane systems there is a misconception that you are making a tent and there are wrinkles in the corners and at connections, but it’s ok because it’s a tent. This isn’t the case at all,” Dreiling said. “We get down to precise standards and prefabricate everything. With a membrane you want to install the largest pieces of material possible and this takes a great deal of precision.”
Pneumatically pre-stressed ETFE systems obtain their integrity from an air inflation system. This system requires routine maintenance and service. The air has to be filtered in some way so as not to put excess moisture or debris into the system. Dreiling offered the example of a 10,000-square-foot roof that requires less than one pound-per-square-foot of air pressure (consuming about the same amount of energy as a commercial fridge) to keep the necessary amount of air circulating.
Even single-layer systems require great coordination of details, as the exact amount of ETFE stretch has to be considered along with the loads it is designed to withstand.
Unfamiliarity with this material is also prohibitive to its use. Through time, confidence in the use of ETFE will spread. Simply put, it has properties and benefits that are unparalleled by other materials.
Christina M. Zweig is a writer at ZweigWhite. She can be contacted at firstname.lastname@example.org.