ETFE: Ethylene-Tetra-Fluoro-Ethylene copolymer, or ETFE, is a lightweight material used in the construction of large-span roofing, skylights, and facades. It finds application as an alternative to glass, where high light and UV transmission are requirements.
Requiring less structural steel support than traditional glazed systems (rendering it easier to install and typically lower cost), it is often considered a value-engineered option over glass roofing.
ETFE Foil is a plastic polymer related to Teflon and is created by taking the polymer resin and extruding it into a thin film. Transparent windows are created either by inflating two or more layers of foil to form cushions or tensioning into a single skin membrane.
ETFE has excellent chemical, thermal, and electrical properties, as well as superior resistance to abrasion and cut-through.
Over the past twenty years, awareness of ETFE and its uses in construction projects has increased. High profile projects such as the Allianz Arena in Munich and the National Stadium Bird's Nest, Peking, have brought ETFE into the limelight.
Today, ETFE is increasingly being specified on a wide range of projects in retail and commercial developments, and sports facilities, including aquatic centres and stadium roofing. A key factor is its contribution to “green” construction – due to its light weight (requiring minimal energy to produce, transport, and install), its full recyclability, high heat retention (reducing energy costs for enclosed structures), and it’s transparency (reducing day lighting costs), it is becoming highly sought after for projects requiring Green Star certification.
Weighing approximately 1% of the weight of glass, ETFE (both single layer ETFE as well as multiple layered ETFE cushions) are extremely light weight. ETFE therefore imposes less dead load on the supporting structure, requiring significantly less structure than an equivalent sized glass structure. Each ETFE cushion has a minor weight of only 0.5 – 1.0 kg/m² for the cushion and 10 kg/Lm for standard extrusion.
Alongside its low weight, another major benefit of ETFE is its high translucency. Transmitting up to 90% light, it is chosen for projects such as stadia with grass surfaces where full spectrum natural light and UV transmission is essential to maintaining plant growth. The ETFE film also absorbs a large proportion of infra-red light, a quality which can be exploited to improve buildings energy consumption.
When high levels of light transmission are not required, ETFE film can be printed or fritted, with a range of patterns to reduce solar gain while retaining transparency. The film can also incorporate a white (or other colour) body tint to render the foil translucent. Furthermore, when multi-layer cushion systems are used, outer and inner layer of ETFE foil can be printed to allow light transmission to be varied thereby adjusting the shading coefficient.
ETFE cladding can be supplied as a single layer membrane supported by steel cables or as a series of pneumatic cushions with a minimum of two and up to 6 layers of ETFE.
A single-ply ETFE membrane has an approximate Ug value of 5.6 W/(m2K), compared with a standard three-layer cushion which can achieve a Ug value of 1.96 W/(m2K) -- a better insulation value than triple glazing when used horizontally. (The Ug -Value of a triple glazing unit is around 0.7 W/ (m²K) and therefore three times better than a 3-Layer cushion).
The insulation qualities of ETFE cushions can also be improved by the addition of more layers of foil (up to six in total) or by treating the foil with specialist coatings to enhance the thermal properties.
With an extremely low mass, ETFE cushions limit the amount of reverberation within a room by absorbing the acoustics. The exact sound levels within an enclosure will depend on the properties of the cushions and the project (e.g. size/scale of room, incline of the pillows, materials used inside, and the span of the pillows).
Due to various factors, noted below, ETFE makes a significant contribution to green construction:
ETFE has a melting point of around 260°C. ETFE does not facilitate the spread of flames in the case of a fire since it self-extinguishes and does not produce any flaming droplets or particles. When hot gasses or flames come into contact with the ETFE cladding that is part of the building envelope, it will melt and shrink back from the damaged region, enabling hot gasses and smoke to escape the building.
ETFE has been subjected to international and national standards tests.
ETFE has a fire resistance rating of class Bs1d0 according to British and European Standards (which are highly comprehensive in their classification).
Because it is unaffected by UV radiation, air pollution, and other kinds of environmental degradation, including maritime spray, ETFE Foil has an extremely long life expectancy.
While no ETFE constructions have been in place long enough to acquire a complete knowledge of the foil's whole life cycle, the material has been extensively investigated and tested both in the academic and professional fields.
These studies determined there has been no deterioration or loss of strength, and there is no indication that the material would become brittle or discolored over time. Consequently, the material is expected to have an expected lifespan of more than 50 years.
As a fluorocarbon polymer, ETFE has similar non-stick properties to PTFE, making it 'self-cleaning'. With a low co-efficient of friction typically of 0.23, dust or dirt that lands on ETFE is washed away by rainwater. Normal rainfall is usually sufficient to eliminate excessive build-up of dirt on the upper surface, although the clamped edges typically require some additional cleaning. Recommended cleaning frequency is subject to location and design of the roof. Heat and chemicals cannot be applied to the ETFE film, and the film and extrusions must be treated carefully to ensure they are not scratched. Access methodologies for cleaning and maintenance are designed into the roof system.
Fixing small holes in ETFE cushions are easy to achieve by way of a special tape. The tape is supplied as part of a handover kit, and Fabritecture keeps the tape in stock. The tape has high strength glue on one side. The area is cleaned prior to applying the tape, and once fixed, will last 5-7 years. It is very hard to notice a small repair unless up close. Repairs are checked annually as part of Fabritecture’s Maintenance Contract.
For pneumatic cushion ETFE systems, the air supply system needs annual maintenance involving a visual inspection and air filter replacement.
