Why Specify an ETFE Roof?
Something that architects the world over have been asking themselves in recent years is why they should specify an ETFE roof for a covering membrane as opposed to more traditional materials, such as glass, PVC membranes or PTFE membranes. Of course, the reasons for an ETFE roof being chosen are as varied as the projects that they have, thus far, been used in. However, there are some common factors that make for interesting reading when it comes to this highly versatile and lightweight construction material. Many of these come down to the properties of ETFE foil, which have been exploited to often stunning effect. The most important advantages of ETFE membrane versus glass is the extreme light weight and the transparency, especially for UV-light! Compared to PVC membranes and PTFE membranes, ETFE is the only material with full transparency for the total daylight. The transparency can be varied in a wide range with colored ETFE foil. A further benefit for ETFE roofs is the self-cleaning ETFE foil due to its smooth and antiadhesive surface.
The Properties of ETFE Foil
Its Green Credentials
One of the most important things that anyone who selects building materials for a living needs to know is what sort of carbon footprint it has. From the outset, it should be said that ETFE foil, the membrane from which an ETFE roof is made, is a sustainable material. This includes all aspects of its construction including the extrusion of the film. Being light, it is also an easy material to transport to site, again lowering its carbon footprint, certainly when compared to other options, like cladding material. Once installed, ETFE foil can often be used to enhance the building's thermal design, keeping warm air trapped inside, thus lowering heating costs. It can also provide plenty of natural daylight, thus reducing the need for power to supply electrical lights – a huge advantage in today's ecologically conscious construction environment. Lastly, an ETFE roof is easily recycled at the end of its life. Any waste and old ETFE foil can be reprocessed and made into new ETFE products.
It Lets the Light In (And Keeps it Out)
Offering high degrees of transparency, ETFE foil will allow most rays to pass through it. Depending on the exact application, up to 95% of the natural light that hits an ETFE roof will pass through. This has the highly advantageous benefit of allowing for planting to be part of the design beneath because UV light is necessary for photosynthesis – the process which allows plants to grow. Nevertheless, full exposure to the sun is not desirable in all settings. Here, ETFE foil is still helpful because manufacturers can include a number of frit patterns within the ETFE material. This can be done on a single layer or multiple layers, if preferred. In turn, this allows the shadowing performance of an ETFE roof to be controlled from the outset. Commonly, membranes are printed with various patterns from a standard palette, but individual frit patterns can be specified, if wanted. Furthermore, colorants can be introduced during the ETFE foil's extrusion process allowing for all sorts of tinting options.
ETFE foil is highly elastic, something that cannot be claimed of traditional glazing. Indeed, it has an extremely high breaking point that beats just about anything else, so it can stand up to a very wide number of building applications whilst remaining structurally sound. The tensile strength is rated at 21-23 N/mm² at the limit of the material's plasticity. However, the tensile strength of ETFE foil has been measured as high as 52 N/mm² at its breaking point. Few materials can match such impressive strength for the amount of elasticity offered.
From a building owner's point of view, it lessens costs associated with artificial light and heating. However, the material is extremely good value for money in its own right. Remember that because it is light, transportation costs are low. It also means that sub-structures, supporting frames and concrete foundations can all be designed with efficiency in mind and less other materials are often used as a result of specifying an ETFE roof. Lastly, it should be noted that ETFE foil has been found to be self-extinguishing if exposed to fire. Indeed, ETFE foil has been rated under various international regulations as offering no burning drops, an important public safety consideration.
Stefan Behnisch - Architect
The specifications for our new concept were met perfectly with the use of ETFE as the single layer outer foil for a double facade: light weight, innovative and visually attractive thanks to the hi-tech look of the back span. The use of ETFE was also ideal from a fireproofing stand point. ETFE is very transparent und almost impossible to rip when used in single-layer applications. The foil is light weight, structurally stable, very durable, easy to keep clean thanks to the “lotus effect” and offers an excellent cost-benefit ratio.
Glass and ETFE Roofs Compared
When a comparison between an ETFE roof membrane and a glazed one is made, the first thing that should be noted is that the newer material affords an augmented thermal performance. This is made possible with the multi-layered ETFE foil system which creates as much greater level of insulation than conventional glass panes. When a double-layer pneumatic system is specified, multiple layers of the membrane can be attached to the panels of the ETFE roof with a gap that can be inflated later. By inflating it with only modestly pressurized air, the roof becomes more stable and provides a much improved thermal retention, too. Although a single layered ETFE roof is perfectly possible technically, the ability to trap heat goes up with the more layers that are added. Therefore, double and even triple layered roofs are preferable if thermal insulation is a concern in the building's design.
Another important aspect of an ETFE roof, compared with glass, is the issue of safety. As mentioned, the material has been tested in fire conditions, but it also has advantages in the event of trauma. Should an earthquake strike, or following a collision with the structure, a glazed roof will often shatter and this can be extremely dangerous for anyone who happens to be beneath it. Conversely, an ETFE roof will not send shards falling down and can even 'bounce' or deflect impacts away.
Maintenance of an ETFE Roof
Because it has non-adhesive surface properties, an ETFE roof is self-cleaning in terms of the usual grime and dust that it will come into contact with. Even larger debris will not stick to the roof and be washed down by rainfall. Nonetheless, installed roofs should be subject to an annual inspection to make sure that all of the components, including the substructure, do not require any maintenance works. An inspection regime should include includes checks on the air inflation of multiple layered sections of ETFE. Given the low amount of maintenance required, this makes an ETFE roof easy to specify, safe in the knowledge that few maintenance issues will crop up.
- ETFE roof is 1% the weight of glass
- ETFE foil can have a better thermal performance than glass