TEXTILES.ORG
Retractable fabric systems are poised
to transform outdoor spaces.
So you thought retractable fabric structures were a late 20th century phenomenon sheltering sports stadia, outdoor shopping malls, and en plein air cafes? Think again.
Forms of retractable fabric roof systems date to Roman times. The Coliseum’s vast seating area, the cavea, was covered with a retractable cotton membrane or awning, operated by Roman sailors. Called a velarium, it provided shade and modest protection from the elements. Its primary use was to create updraft ventilation, generating a cool breeze for Roman patrons. According to Nic Goldsmith of FTL Design Engineering Studio, in New York City, “Attachment points [for retractable awnings] can still be seen today on most Roman coliseums.”
Fast-forward some 20 centuries. In the 1960s Frei Otto, the much-lauded German architect and structural engineer, developed designs for retractable roof systems. Goldsmith cites his 1968 roof that spans the ruins of the 12th century imperial Bad Hersfeld Abbey as one of the first.
“In Europe there are more retractable roofs,” says Peter Fervoy, business development manager at Uni-Systems in Minneapolis, Minn., which recently developed the innovative En-Fold retractable roof system. “Europeans are more innovative and forward thinking about design and retractable roofs—and less risk averse—than in the United States.”
Categories
Goldsmith breaks applications for retractable fabric systems into three general categories. First are the large retractable sport/entertainment stadia, such as the new BC Place in Vancouver. “Most are designed and engineered by Schlaich Bergermann using radial cable geometries, but also some by Walter P. Moore, which use rectangular rail systems,” Goldsmith says.
The second application is terrace and roof systems, such as En-Fold, or designs of Clauss Markisen often used for hospitality, business and civic structures. The third is umbrella-based systems, which were designed first by Frei Otto and subsequently by Bodo Rasch. Many have been developed in the Middle East, such as umbrella systems designed by Rasch that have been in service in Medina, Saudi Arabia, since 1992.
Cable and frame are the primary types of retractable fabric systems, both of which have pros and cons, depending on the scale and needs of a project. Tensioning cable systems can be difficult, and in windy conditions they can generate high reaction loads in the buildings to which they are attached.
On the upside, according to Peter Katcha, director of North American sales for SEFAR, “Cable is a more efficient structural form for retractable fabric; it has a more open feel and is more compact for storage. Frame systems are less evolved, leave more structure in place when the system is closed, and are more difficult to store. On the other hand, frame systems minimize load issues for a building and thus can be a better solution when retrofitting a building site.”
Challenges
Historically, retractable fabric structures have been consumer-challenged. Usually custom, one-off designs, they have been cost-prohibitive for most and plagued by mechanical problems in the drive system that were difficult to trouble-shoot, as each was unique. “Projects often start at $150 per square foot, but can easily be double that,” Goldsmith says.
For retractable fabric structures to be viable in the 21st century, Fervoy knew they must have a robust system that would operate multiple times a day, every day, be corrosion resistant, and last for 30 years or more.
A high-performance retractable tensile structure, En-Fold is designed for commercial applications from outdoor dining spots to sports facilities. It is a fully automated system and, with appropriate frame configurations, can withstand 90 mph winds and snow loads up to 30 psf. En-Fold is designed to shed water in the direction of its slope, and it can be configured in vertical positions.
The system debuted with two retractable awnings for Miami Beach’s Soho Beach House hotel in 2011. Uni-Systems lists Minute Maid Park in Houston, Texas, which opened in April 2000, as its first retractable (PTFE) roof. The company is designing a retractable pitch and a retractable roof for the Grand Stade FFR, a rugby stadium outside of Paris scheduled for completion in 2017.
Katcha thinks En-Fold’s key to success is that it is pre-engineered and fills a niche between off-the-shelf canopies with limited spanning and wind-load capacity and one-off retractable structures that can be cost-prohibitive. Also, with any of its En-Fold systems, Uni-Systems can trouble-shoot operating problems by accessing the control system online and resetting it.
Charles Duvall of Duvall Designs, Rockford, Maine, has designed several retractable fabric structures since 2007, including a Grand Cayman Island project with three separate but related systems. One vaulted element easily sheds water and covers a large oceanfront area. His large, comprehensive system for the Georgia Street Mall in Indianapolis spans three streets and is operated by an iPad.
Duvall also believes that the challenge is to design a system that will work repeatedly over time—motorized or not—and be cost-effective. “Often one mechanical problem will create another problem elsewhere in the system,” he says. “It’s an issue when each project is a one-off to find the vulnerability in a system.” He also believes some projects suffer from being “over-engineered,” making it too heavy and expensive. “Some guy is sitting at his desk, hundreds of miles away, not really knowing the situation. Not knowing he is making it needlessly more expensive.”
The right fabric
Developing appropriate fabric for retractable systems was also a challenge. Not only does a fabric need to be pliable so it can fold easily, it must be waterproof. “The scrim material of SEFAR’s Tenara 4T40 fabric allows for pliability so the fabric can fold for compact storage—something PTFE-coated fiberglass fabrics cannot do,” Katcha says. “The coatings protect the structural scrim from UV damage and water penetration. Most coatings are laminations on top of the scrim. When folded repeatedly, the coating laminate will crack, allowing for delamination and eventual fabric breakdown.”Â
With Tenara, the scrim and coating are essentially one. Tenara provides up to 40 percent light transmission, and it’s lightweight and recyclable.
Uni-Systems has also used Serge Ferrari Precontraint 1002 S2 fabric with its En-Fold system, including the 444 North Capitol rooftop terrace project in Washington, D.C. It was also employed for the Andaz Rooftop, a high-end café and lounge atop a historic San Diego hotel.
A promising future
Most people in the industry think the future for retractable fabric roof systems is bright. If mechanical issues can be totally resolved, retractable fabric systems are poised to effectively transform and commercialize what was previously only outdoor space, expanding the reach of hotels, resorts and restaurants.
“The future of kinetic architecture is promising,” Katcha says. “When compared with glass, wood or metal, retractable fabric systems have the ability to fold, span large spaces efficiently and are relatively light in weight.”
Given the inquiries Fervoy receives daily from the hotel, resort and sports industries, he thinks the numbers will only increase. “They need spaces for large events and they want to maximize under-utilized spaces such as rooftops and courtyards,” he says. “Such sites can’t build permanent structures, but they can add more revenue generating spaces with a retractable roof. Traditionally they would be renting tents for clients. A retractable system is much better.”
Other uses might include outdoor performance venues. Fervoy predicts retractable fabric systems will have a future with amusement parks and zoos. When cost-effective, they have a market with green houses, agricultural businesses and water treatment facilities.
Duvall foresees future retractable fabric systems being interactive. “I’d like to see a system whose sensors would be interactive with light, people and the weather. It would be a nice add-on and not too expensive. It will happen.”
For Katcha, adaptable commercial environments are the future. “Retractable fabric structures are more adaptable and sustainable—the demand will only increase for civic, sports and hospitality uses,” he says. “What keeps more from being installed now is the price. A client likes it but cannot afford it. But that’s changing.”