For applications in which glass would typically be used, ETFE delivers superior thermal performance. For double- or triple-layer pneumatic systems, multiple layers of film are welded into panels inflated with low-pressurized air to stabilize the film and provide the system’s thermal property. In a single-layered application, an R-value of approximately ‘1’ can be achieved. In a two-layer system, an R-value of about 1.6 can be reached. A three-layer ETFE assembly has an R-value around 0.51 K·m2/W (2.9 sf·F·h/Btu) or a U-value around 1.99 W/m2·K (0.35 Btu/(h·sf·F). Integrating internal blankets of aerogel into the system further increases the level of thermal performance.
Another key characteristic of ETFE is the air inflation system. A pneumatic ETFE cushion system is generally fed by one or more inflation units. Each unit consists of two redundant blowers forming a backup system for guaranteed structural stability. A series of pressure sensors continuously monitors the internal pressure of the ETFE cushions, maintaining them between 240 and 290 Pa (5 and 6 psf). One unit can feed a roof ranging from 1400 to 2325 m2 (15,000 to 25,000 sf). They are UL-certified and run on an 110V power, with a power consumption of less than 1kW.
Due to the non-adhesive surface of ETFE, deposits are washed away by rain, resulting in a ‘self-cleaning’ effect. However, it is necessary to perform yearly inspections, including all necessary checks on the air blower system and filter replacements. The ETFE film and its attachments must also be inspected to prevent any further deterioration.
Overall, ETFE film structures are low-maintenance systems. Should there ever be a puncture or tear—which typically results from flying debris from weather-related instances—repairs in the field can be done. In these instances, if it is a small hole or tear, the membrane can simply be repaired with a patch. If it is a larger tear in the film, replacing the affected ETFE panel can be done without needing to replace the entire ETFE roofing system.
ETFE films have been rated under various national and international standards for fire resistance as self-extinguishing with no burning drops. ETFE is classified under several different standards, including:
- ASTM E84, Standard Test Method for Surface Burning Characteristics of Building Materials, Class A;
- UL 94VTM, Tests for Flammability of Plastic Materials for Parts in Devices and Appliances−Thin Material Burning Test, Class 0;
- EN 13501-1, Fire Classification of Construction Products and Building Elements−Part 1: Classification Using Data From Reaction to Fire Tests, Class B-s1-d0; and
- National Fire Protection Association (NFPA) 701, Standard Methods of Fire Tests for Flame Propagation of Textiles and Films.
Due to the material’s high resistance and elasticity, ETFE is ideal where sudden extreme loads, such as earthquakes or blasts, may occur. Unlike glass, which can shatter and cause major concerns under such situations, ETFE deflects the heavy load.
Conventional construction versus ETFE
There are several basic differences found between conventional construction and building with an ETFE assembly. With conventional construction, heavy weight and rigidity are the standard requirements—therefore, the design must follow limited geometry, often leading to high construction and development costs and limited aesthetic options.
With ETFE, structural form and integrity are achieved through tension. This allows architects to break away from traditional geometric shapes and create freeform designs cost-effectively. To create a structure that harmonized with its surrounding landscape, the design-build team for Empire City Casino at Yonkers Raceway designed an exotic porte-cochere that appeared to emerge out of a nearby hillside. As the structure was a gateway to nighttime entertainment, the design also incorporated custom-colored light-emitting diodes (LEDs). Achieving this dynamic aesthetic cost-effectively through conventional construction would be impractical, if not unfeasible.
ETFE also features numerous engineering benefits. In conventional post-and-beam construction, structure is created through compression. With ETFE, structural loads are carried by internal air pressure compensating for external wind and snow pressures, resulting in a lightweight structural element. It can be difficult to span great distances without providing support columns with conventional construction. With tensile architecture, weight is comparatively negligible and larger spans are significantly easier to achieve.
British architect Sir Michael Hopkins has summarized the unique benefits of tensile architecture.
“Increasingly, we are exploring highly-efficient multi-functional elements, where the structural performance, enclosure, light, and thermal transmittance are combined in a single element,” he said. “These are the reasons we use membrane.”
