Weather or not—fabric measures up
With a great selection of materials available, fabric structures adapt to different climates and project needs.
Specialty Fabrics Review | December 2012
By Barb Ernster
Trying to find the right solution for the right application in a particular climate is generally foremost in architectural work. The issues to be addressed in developing building envelopes or employing tension membranes are no different than using more conventional building materials, says David Campbell, principal and CEO of Geiger Engineers in Suffern, N.Y. “We’re interested in accomplishing the same functions with one or two or three layers of composite textile. Is it a challenge? No, because of the wonderful selection of great materials that addresses different, and sometimes conflicting, requirements.”
In hotter climates, an outer layer glare reduction fabric that reflects the sun’s rays can reduce the thermal gains in a building and the need for more cooling. In cooler climates, increased daylighting allows the solar energy in where the heating benefits are welcome, he adds. “Different fabrics and coatings and combinations of materials in layers can be the same as conventional construction.”
Breakthrough in thermal properties
New technology and innovations are driving the industry to better solutions in dealing with climate considerations. Aerogel technology is proving to be an ideal solution for tensile membrane structures in cold and hot climates. Developed by Birdair Inc. in Amherst, N.Y., Tensotherm™ is a composite of insulating Lumira™ aerogel sandwiched between two layers of PTFE-coated fiberglass fabric. Just a thin layer of the aerogel provides a thermal barrier, preventing heat loss and solar heat gain—retaining cool air in warm conditions and warm air in cold weather.
Campbell, whose firm consulted on its development, says the product also meets increasingly demanding energy and building codes required throughout North America. It can also absorb sound and it allows light transmission, which is a huge architectural asset today, he adds.
The Dedmon Center at Radford University in Radford, Va., was the first installation of Tensotherm in 2009. It was used to replace an air-supported dome that Birdair built in the 1980s, with a new single skin membrane roof. One of the challenges for the Dedmon project was to meet current energy codes. The Tensotherm membrane brought the insulating R-value to 12.5 (compared to a single layer of PTFE fiberglass, which has an R-value of ˃1). Its translucency allowed daylighting with minimal solar energy gains, and its hydrophobic property repels moisture that can occur with vapor penetration.
Moreover, the acoustical performance of the arena was improved. “The sound absorption qualities increased immensely. That performance attribute quadrupled the use of the facility from being only used for basketball and intramural sports to a performance and concert arena,” says Kevin Mayer, vice president of business development at Birdair.
In addition, aerogel’s innovative thermal insulation properties are important in single-layer membrane structures because its insulating performance doesn’t degrade over time. “The traditional double-layer systems were good attempts to try to solve a problem, but the use of aerogel technology with PTFE-coated fiberglass membrane truly solves the insulation problem that has been plaguing the industry since its inception,” says Mayer. “It has the potential to move away from strictly being a tensile shade product to offering the traditional benefits of daylighting, freedom of form, lightweight and long-span structure advantages, while also providing insulation, G-value performance and acoustical benefits.”
Birdair has conducted energy modeling in the Middle East where the temperatures in summer can reach 130 degrees. Tensotherm has demonstrated an impressive effect on the Solar Heat Gain Coefficient (SHGC) or G-value, which is an effective measure of performance of a membrane roof in a hot climate, says Martin Augustiniak, Birdair’s director of engineering. Energy modeling is currently under way in parts of Europe, Japan and other areas of the world where the cost of energy is significantly higher than that of the Middle East.
A collaborative solution
When Arizona State University decided to embark on its Polytechnic Academic Complex in Mesa, Ariz., design thinking was focused on creating a sustainable, environmentally healthy campus, even though unforgiving heat, strong winds and arid conditions are old news to residents of the southwest United States. “The design intent was to create dynamic pedestrian environments that offer a cool, pleasant experience,” says Beau Dromiack of RSP Architects, Minneapolis, Minn., lead designers of the project. “The buildings are designed around three-story atriums that are fully covered by perforated metal panels on the horizontal surfaces and open on the vertical surface for ventilation. Each atrium has three large fans for increased air circulation and the north and south ends are open to create view corridors and increase air movement.”
Sustainable building strategies included cloaking the roofs with a bright white EPDM membrane that reflects sunlight away from the buildings. East and west facing prefinished and weathering, perforated steel shade screens projecting 1.22m from the buildings’ skin protects from the sun. Teflon®-coated fabric, Trex® recycled wood and photovoltaic panels have also been used to shade the structures. Locally made wire mesh planting screens encase the exterior stairway towers and create a “planting apron” that runs along the lower edge of the exterior perforated screen panels.
The project is also a great example of how a climate can affect change in membrane choices, says Steve Fredrickson, national sales manager at Serge Ferrari North America, which supplied the tensile mesh membrane for the student bookstore. Employing a mesh rather than a solid fabric allowed for some airflow and reduced the amount of heat buildup under the canopy.
“Any products that you can provide to assist in the design and construction of a building with respect to energy savings, light transmission and glare reduction are all well received in the architectural community,” says Fredrickson. Textile facades used to reduce the impact of energy on a building while still allowing the transmission of natural light is an enormous market, he adds. Natural light is an important factor in building designs, especially in North American markets, which have an influence on the rest of the world. “It’s got a lot to do with how it impacts everyday life for people—nobody wants to work in a bunker. At the same time, it reduces the amount of energy used for lighting.”
The importance of codes
Manufacturers also need to address local building codes for both permanent structures and temporary buildings. Wind, snow loads, and fire codes are the most common ones, but lately even seismic activity can be on the list, based upon the region. Certain areas in the U.S., such as California, have now applied seismic considerations as part of the design requirements that must be met prior to approval for construction.
Coated fabrics that are pretensioned in the length and width prior to coating offer a stable platform from which all kinds of structures are being built, says Fredrickson. Serge Ferrari Precontraint® technology is a patented manufacturing process of applying tension of the warp and weft yarns equally throughout the coating process, which gives the textile dimensional stability in all climate conditions. It’s a lot like the foundation of a house: any movement of the foundation will affect all portions of the construction and the final product. Precontraint was designed to resolve these issues with its consistent stability.
Serge Ferrari has several longevity studies showing that PVC structures have lasted well beyond 20 years due to the stability of their coating process. An airbus hangar located in Germany, for example, after 22 years had residual tensile strengths of 97 percent in the warp and 84 percent in the weft compared to its original strength. “Combine this with the Texyloop® recycling facilities’ ability to completely recycle the membrane after its life and you now have a very viable membrane for modern construction projects,” says Fredrickson.
Dealing with moisture
Wet or humid conditions can also affect the long-term stability of a fabric, which can weaken and lose mechanical strength if the yarns absorb water. Germany-based Mehler Texnologies GmbH has a line of architecture products called VALMEX® MEHATOP F that are made of multilayer, composite material with densely-woven, low-wick yarns in the carrier fabric. The fabric is finished with a double topcoat of directly weldable, PVDF lacquer developed by Mehler, which has a protective and refining effect.
The low-wick property protects the membrane from penetration of molds, fungus and pests from the outside, but also from humidity and even vapors that can attack the fabric from the inside, such as in a restaurant. Even under extreme climate conditions over long periods, the membrane will maintain its unique appearance.
“Most fabrics are not equipped with low-wicking yarns. That’s a weak point for a permanent textile enclosure. If water is absorbed into the yarns along the cut edges, they lose mechanical strength and the fabric may collapse,” says Paolo Giugliano, Mehler’s product manager, architecture. There are few low-wicking fabrics on the market, he adds.
The application of fabrics in building envelopes and tension structures boils down to what you want to keep out and what you want to let in, Campbell says. Climate is just one factor in a whole series of questions that must be addressed. In the end, a properly designed structure with the right fabrics can yield a 20- to 30-year life span or more, and retain nearly 100 percent of its original value.