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July 20, 2016

Problems with Poorley Designed ETFE Roofs and Canopy’s

Have you ever looked at an ETFE tensile structure and wondered at its almost effortless organic fluidity, its ability to transvers seamlessly from the confinements of interior structural restrains towards the free forming, reenergising transformation of nature? Well I do all the time; however it’s not always what it seems! Done well it can literally take your breath away, done wrong and ETFE becomes an extremely problematic architectural choice, especially proven in providing Problems with ETFE roofs and canopy’s. This blog post is strickly to show you want to look out for and how to avoid it. 

Stop Promoting ETFE for the Wrong Projects

I know this may sound poor form coming from a tensile architectural company with specialisations in ETFE to say “stop promoting ETFE.” Especially as we only recently wrote a blog entitled ‘Why ETFE Membrane Roofs Are the Future‘. However, we do have our reasons and I hope to objectively explain why within the following blog post.

It was back in the 1980’s when ETFE was first formed into a membrane fabric and then used in its first small scale architectural insulation. However, it was really back in 1990 when the development of ETFE roofing took its first baby steps into the world of architecture. The Chelsea and Westminster Hospital in London saw the first evolution of an ETFE roofing system emerge. Since then ETFE membrane roofing has literally been sold as a must have accessory to all architects and their clients. Reasons given are often quite valid, 30% upwards savings on construction costs, reduced installation time, energy savings and the fact that the whole visible light spectrum can enter. This allows large amounts of natural light to flood the building’s interior, creating a much “brighter and open space feeling” than traditional glazing.  Designed, Engineered, Fabricated and Installed correctly this is can be true. However, if designed and engineered incorrectly it doesn’t matter how good the fabrication and installation is, you will forever curse the time you first heard the syllables of E.T.F.E. Architects, specifiers and especially, the sales men within our industry, tasked with promoting the use of ETFE need to stop thinking about getting the contract secured and start thinking is ETFE right for this project? Will it benefit the client and building usage in the long term? Unfortunately these questions are often overlooked when ascetics and procurement costs are the primary force behind reasoning.

Typical Problems with ETFE Roofing and Canopy’s

As with all construction materials and designs we need to actively decide which is best suited for the job at hand. The same must be said about tensile membrane architecture. Whilst ETFE offers significant benefits it also has numerous downsides, particularly when it comes to roofing! The following will hopefully outline Typical Problems with ETFE Roofing and Canopy’s so you can ensure its done correctly and avoids rookie mistakes; the first being its design.

Design & Engineering

The design and engineering of ETFE should not simply be for confirmation of structural loads and form finding to ensure it mirrors the leading architects design intentions. It should also focus on the actual life usage of the tensile installation along with its access for maintenance, ability for cushion replacement, ability to control internal temperature build up and safety backups should cushion compression fail leading to potential structural collapse. Unfortunately, far too many are focused on the overriding project costs rather than design suitability and lifespan operation costs. This also impacts greatly on safety. There are documented instances whereby storm damage has caused the rapid deflation of poorley ETFE cushions resulting in severe fundamental structural damage to steel works. In one particular instance this happened on a hospital, only days before its opening with the ward below being flooded and the building structural integrity being compromised. With such glowing facts staring in our faces, it beggars belief why we do not see companies designing and engineering ETFE roofing and canopies to allow for operational lifespan and potential failures. I have to say this can only be down to the cost implications. A fundimantal aspect which we at Airsculpt first look at, is how to maximise the design and engineering, to enusure operational lifespan and compliance with all weather loads. 

Solar control Issues

ETFE membranes are extremely effective at allowing the full spectrum of natural day and sunlight to enter the space beneath. After all that is why the product is used on large scale botanical installations such as the Eden Project.  However; it is not so good at allowing the resulting heat build-up to escape. By the Eden Projects own admissions controlling temperature with the ETFE Bio-Domes was not an easy task, nor was it cheap. This however, is something which can be dealt with during the design stage, but specifiers need to be informed about the solutions at the beginning of tendering and not after the project has been awarded, as this alters the design and costs. There are various ways to control temperature build up within ETFE structures, including printing on the inside of the cushions, internal ETFE movable layers which can alter the degrees of light penetration and ventilation hatches etc. Awkwardly we seldom see this issue being brought to the attention of the end client until it is too late. Once an ETFE roof has been fabricated and installed it would be practically impossible to implement design and fabrication changes needed to rectify this issue.

As a company Airsculpt has been called upon to provide solutions on countless ETFE Roofing projects, whereby the space beneath is unusable on hot sunny days. In many instances building owners have had to accept a reduction in rent due to such issues, with tenants later invoking lease clauses within tenancy agreements due to unacceptable working conditions being cited.  Depending upon the building, this can cost land lords hundreds of thousands a year.

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Puncture and Deflation of ETFE Cushions

With ETFE being used as a roof construction material, Puncture and Deflation of ETFE Cushions is an inevitable problem that will occur with incorrectly fabricated cushions – Fact! There are several reasons as to why this happens; however, we’ll focus on the two main reasons which cause ETFE Cushions to deflate.  If desinged and specified correctly, it must be stated that risk of ETFE cushion punctures can be minimised or removed all together. 

The first reason is actually complex yet simple to explain.  To create the cushions, the desired size and shape it first needs to be cut, then the two sections of ETFE need to be welded together to create an air-tight seam. Within the world of ETFE construction each supplier / fabricator will have their own highly protected and unique way of welding the seams in an attempt to create a perfect bond between the layers, with some being better than others. However, this is a manual process meaning it is almost impossible to create a uniformed seam that is perfectly bonded. Also, you have to factor in human error during this process. This can result in irregular bonds that when under pressure – which ETFE roofing and ETFE Canopies are, the seams can begin to separate over time causing air-leakage and cushion deflation. Trying to remedy this on site is actually harder than if the repair was done back in the factor. Therefore, any repair will inevitably need to be regularly inspected and repaired yet again.  The larger the ETFE Cushion span the more forces are placed upon the seam, meaning larger ETFE installations are more likely to suffer from this problem. This is why Airsculpt’s fabrication relies heavily on an automated system and highly process driven fabrication methodology.

The second reason is easier to explain yet no less problematic. Simply put……BIRDS! Birds love to land on rooftops and peck at their food to break it up before swallowing. The bigger the bird the more powerful their pecking action will be. It is widely known that ETFE roofs and Canopies installed nearby or close to the sea suffer the worst of this. This is because Seagulls use the ETFE Roof membranes as an ideal platform to stop and peck at shellfish, crabs and the occasional stolen chip. This often vigorous and powerful pecking action causes punctures and tearing to the ETFE Membrane. However, due to the gulls moving further inland and close to refuse dumps, we are seeing such sized birds causing issues all over the place. As each installation should have a programmable control air pump, the pump works harder in an attempt to keep the cushion inflated.  Unfortunately, industry standard pumps are not capable of sustaining this for long so the cushion will deflate within a week or two. This then allows condensation to enter and water droplets to accumulate inside the cushion with replacement being the only real solutions to remove the blooming and discolouring which this causes. To avoid this, Airsculpt automatically incorporate bird deterrent systems and rain suppressors which also prevent bird damage. 

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ETFE Condensation

Geographic location can have a profound effect of the condensation problem. Tropical locations that have cool nights, hot days and a general high level of humidity are particularly susceptible. ETFE installations located in areas that maintain a high level of atmospheric humidity usually include a dehumidifier air system. However, these systems can be easily overwhelmed by the levels of humidity. Where such instances happen the condensation cannot be removed from inside the ETFE cushions and the build-up of condensation can result in puddles forming inside the ETFE cushion itself. In some cases, these can then become stagnant resulting in significant discolouration. This problem has been occurring in Singapore for a prolonged period of time which has led to a total ban on all new ETFE cushion projects. Only single layer ETFE is now permitted. As with all of Airsculpts installs we look at the implementation dehumidifies to safeguard against such issues from the get go.

ETFE Rain Noise

Apart from Solar and heat issues, Rain Noise on ETFE is perhaps the second most annoying factor which is talked about when it comes to ETFE Canopy and ETFE Roofing installations.  It has often been likened to sitting inside a drum (deafening).  Unlike glass, ETFE is a membrane fabric which will resonate sound exactly like the skin on a drum. Add the factor of inflated cushion design and you get increased amplification. Many Schools, Colleges, Shopping Centers and Commercial Buildings have had an ETFE Roof put in over an atrium, reception or even library area so that light floods the space beneath; the reasons are so the area is made to feel more useable. However, this often turns out to be the opposite if rain suppression isn’t included in the design. Again, this is something we at at Airsculpt look at from the get go.

Eradicating ETFE Roofing & Canopy Problems

Solutions for Eradicating ETFE Roofing & Canopy Problems are relatively simple and widely known. It is all about selecting the right supplier and ensuring Design & Engineering looks at the operational side of the structure. As they say, you get what you pay for!! ETFE Roofing and Canopies can provide all the benefits as mentioned in the second paragraph above, but only if the project is done correctly and with a supplier who understands the issues and how best to prevent them, as this needs to be dealt with during the design and engineering stage. This may mean costs need to be looked at in order to provide the right solution, but don’t you think this is worth it in order to have an ETFE Roof or ETFE Canopy which actually operates in accordance to design intentions? Although the construction industry is hooked on an approach of ‘cheapest is best’, it really is the responsibility for leading Architects to ensure specifiers and quantity surveys don’t just look at the bottom line. But at companies and suppliers whom can demonstrate core competences in understanding the importance of engineering and for providing solutions that Eradicate ETFE Roofing & Canopy Problems.

Don’t be a victim of ETFE roofing problems, Airsculpt prides itself on our expertise and problem solving approach to design and engineering within tensile architecture.

For further information and understand what solutions may work best for you on your ETFE project, call Airsculpt on +44 (0)1249 811700 or email us at info@airsculpt.com

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