Indulgent yet responsible fabrics

Here we are in  the 21st century, with its acute global issues of over-population, loss of natural habitat, carbon emissions and pollution of all kinds — in a nutshell the specter of diminishing resources and climate change.   What’s a good architect to do?  Some are saying that fabric structures – that ancient way of providing shelter – is in a unique position to contribute significantly to a more sustainable built environment.  Fabric structures  have a modest carbon footprint, minimal post-construction refuse, daylighting and water-harvesting capabilities,  and are relatively  easy and inexpensive to replace.     According to Thomas Fisher, Dean of the College of Design at the University of Minnestoa, “Living lightly on the land is a key principle of sustainability, and fabric allows for that more effectively than almost any other material.”

Architects are finding new and unique ways of using fabric because there is a not so new polymer in their tool kit:  ETFE (ethylene tetrafluoroethylene).  This – some say- is the building material of the future.  It’s a transparent plastic, related to Teflon, and is just 1% the weight of glass, but it transmits more light, is a better insulator and costs 24% to 70% less to install.  It’s also resilient (able to bear 400 times its own weight, with an estimated 50 year life span), is self cleaning (dirt slides off its nonstick surface) and it’s recyclable.

Architects started working with ETFE about 15 years ago, but the material got a boost by being used in the 2008 Beijing Olympics, where it’s an integral part of the distinctive designs of both the Beijing National Stadium (called the Bird’s Nest – see photo on right)  and the Aquatics Center (the Watercube, at the left).

ETFE has been described as a sturdier version of plastic cling wrap.  It can be used in sheets or inflated into pillows.  The 750,000 square foot Watercube is the largest ETFE project ever.  It is clad entirely in blue ETFE cushions.  It’s interesting to note that the Watercube is the first time the Sydney, Australia based PTW Architects, who designed the building, had ever used the fabric.  They were that confident.  Some bubbles in the design span 30 feet without any internal framing – a distance that wouldn’t be possible with other materials.

On an aesthetic level, the cushions reinforce the building’s theme. Their pillowy shapes evoke a bubble’s roundness, and their triple-layered construction, which mixes layers of blue film with transparent film, gives the façade a sense of depth and shifting color. And there’s  the fun factor:  ETFE comes in different finishes and colors, and can be lit from within using LED lights or decorated with light projections like a giant movie screen as in the picture.   Once the Olympics  started officials were able to transform the Watercube walls into a giant TV screen showing simultaneous projections of the swimming activities taking place inside.  It can take myriad shapes too: strips can be heat-welded together like fabric squares in a quilt.

But what is ETFE – and what does it mean that it’s related to Teflon?

ETFE was developed by DuPont, working with NASA, as a thermo plastic version of Teflon.  It was designed to have high corrosion resistance and durability to hold up under oppressive cosmic radiation that NASA would expose it to.

But Dr. Stefan Lehnert, a mechanical engineering student at the time, was looking for better foils for the sails on  his sailboat.  He experimented with ETFE and found a transparent, self cleaning, durable and very flexible material with just 1% weight of glass.  It also expands to three times its normal length without losing elasticity and offers shade and insulation control. Dr. Lehnert founded Vector Foiltec in Germany in 1982, where they sold ETFE as the Texlon Foil System.

Today it’s being touted as the new green alternative.  Why?

Affiliates of Brunel University in Middlesex and Buro Happold Consulting Engineers in London did a study of the environmental effects of ETFE manufacture and use for building cladding (it’s primary use).  The study compares ETFE foil cushions to 6 mm glass and concluded the following:

“ETFE foils can improve the environmental performance of a building from two points of view:  there is the opportunity to reduce the overall environmental burden incurred by the construction process itself; and there is also the opportunity to reduce the burden of the building during its lifetime.  This is all dependent, however, on the ability of the architects and engineers to take advantage of both the flexibility and limitations of ETFE foil cushions.”

Using ETFE can accrue LEED points by giving you opportunities for daylighting a structure, reduction of steel for support structures, and it can save on transport costs because of its light weight.  If you reduce the tonnage of steel, and reduce the raw building materials you have a real capacity to lighten up a building.  The Texlon Foil System, according to the company, has low energy consumption during its manufacturing process ,  much of which includes recycled materials.  The film itself is recyclable – the recycling is aided by the absence of additives in the manufacturing process, requiring only the ETFE and heat.    It can also be a tensile structure for renewable energy sources such as photovoltaic panels and provide shade to keep buildings cool in hot climates.

Larry Medlin, professor and director of the School of architecture at the University of Arizona, says:  “Fabric’s multiple capabilities from catching water, trellising plants, daylighting, and providing shade for cooling, are being looked at seriously,” he says. “Fabric can contribute to a regenerative landscape. This is important. It can’t be overlooked.” Medlin also explains that using fabric structures is one way to bring the indoor outside, as in the Edith Ball Center (shown at right), a project that required re-conceptualizing with a more innovative approach. Instead of being enclosed, the Center’s three community pools — lap, therapy and swimming — are under a dynamic, open fabric system that can be adjusted to season and climate.

But what about the material itself?  And is it really recyclable?  There are no life cycle analyses of ETFE that I know of  (please let me know if you’re aware of one and I’ll post it here) so until we know the carbon footprint issues of this product I’m still a bit skeptical, although there seem to be many points in its favor.

ETFE – ethylene tetrafluoroethylene – is a fluorocarbon based polymer, aka “fluoropolymer” – a type of plastic.  We did a blog posting on flurocarbons a few weeks back which can be accessed here. So the material is of the chemical family consisting of a carbon backbone surrounded by fluorine – part of the “Teflon” family of chemicals.  These chemicals as a group are highly suspect, since PTFE (which is the building block for Teflon) has been found to produce PFOA as a by product.  From our blog post:  ” They (perflurocarbons) are the most persistent synthetic chemicals known to man. Once they are in the body, it takes decades to get them out – assuming you are exposed to no more. They are toxic in humans with health effects from  increased chloesterol to stroke and cancer. Alarmed by the findings from toxicity studies, the EPA announced on December 30, 2009, that PFC’s (long-chain perfluorinated chemicals)would be on a “chemicals of concern” list and action plans could prompt restrictions on PFC’s and the other three chemicals on the list.”  The Stockholm Convention on Persistent Organic Pollutants states that PFOS is used in some  ETFE production.

ETFE is not a derivative of a petrochemical.   It is  manufactured from fluorspar (CaF2), trichloromethane (CHCl3) – called chlorodifluoromethane (CHF2CL) –  and hydrogen sulfate (HSO4).  Chlorodifluoromethane is a raw material classified as a class II substance under the Montreal Treaty on ozone depleting substances.   Class II substances are scheduled to be phased out but have a later timeline than Class I substances.

The by products formed during ETFE manufacture  are calcium sulfate (CaSO4), hydrogen fluoride (HF) and hydrochloric acid (HCl).  The calcium sulfate and hydrogen fluoride are reused to produce more fluorspar which can be used again as in input into the manufacturing process.

The manufactured ETFE is sold as pellets, which are then heated and extruded into sheets 50 – 200 microns thick.

As one pundit has said: if this is a recyclable product, what chemicals are running off into our water supply?  Do we know what those ETFE chemicals do to humans – not to mention cows, tree frogs or trees –  if ingested?

One thing we DO know about ETFE is that fumes given off at 300 degrees Centigrade cause flu like symptoms in humans, and above 400 degrees C – they’re toxic.  (1)  I have seen articles which say it is combustible and others that say ETFE is considered self extinguishing.  What everyone agrees on is that in the event of a fire, the foil will then shrink  from the fire source, thereby self-venting,   and letting  smoke out of the building.

I can’t make up my mind on ETFE as a sustainable building material.  What do you think?

(1)  .   http://www.buildnova.com/buildnovav3/buildingsystems/TensileFabric/tensilefabric.htm

2 thoughts on “Fabric structures for the new millenium

  1. Charles Irby says:

    Please see the following PDF regarding an environmental assessment of ETFE in comparison to related materials:

    Click to access PAP_MONTICELLI_754.pdf

    1. Thanks for this information Charles. I admit to needing to have help in deciphering the material, since I’m not a chemist. But maybe others can comment? This does sound promising.

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