Endless opportunities

5 October 2013


The cross-laminated tulipwood Endless Stair demonstrates the potential of hardwoods in construction, and AHEC has gone a step further by providing an LCA of the project. Keren Fallwell reports

To say Endless Stair, the cross-laminated tulipwood sculpture erected in front of Tate Modern in London, has caused a stir would be like saying the birth of Prince George in July created a bit of interest.

Of course the wooden structure, which provides wonderful views along the Thames, hasn't attracted the frenzy of the royal arrival but it has received global media attention that's arguably unprecedented for timber. Not only has Endless Stair featured in all the national daily newspapers, including the Financial Times, in the US it's been covered by the New York Times and CNN, and a Google search brings up no fewer than 26 pages, including Dutch, German, Australian, Canadian and Chinese websites.

It's great news for timber, but also for the American Hardwood Export Council (AHEC), which teamed up with de Rijke Marsh Morgan Architects (dRMM) and engineers Arup to produce the sculpture - the landmark project for this year's London Design Festival.

The aim of Endless Stair, AHEC's third collaboration with the London Design Festival, is not only to showcase timber, and US hardwoods in particular, but to promote hardwoods as a construction material.

With its 15 interlocking staircases, the sculpture is inspired by the optically challenging multiple staircases in Escher's lithograph, Relativity, and, while the structural engineering ingenuity of Endless Stair may create as much intrigue, the use of timber is quite clear. The tulipwood is protected by three coats of lacquer so the make-up of the CLT is visible, and AHEC has applied this concept of transparency further by producing a life cycle assessment (LCA) on the entire process.

AHEC European director David Venables is understandably pleased with the project.

"It has everything we could wish for: great inspirational design, a serious structural challenge for the engineers, a pioneering use of one of our most intriguing timbers, and the first ever scientifically-based environmental profile for a timber structure," he said.

"Add to that the winning combination of the London Design Festival as a platform and Tate Modern as a venue and you can see why I'm grinning from ear to ear."

At the official opening of Endless Stair, the US ambassador to the UK, Matthew Barzun, praised two key elements of the project - its creativity and sustainability.

The creativity is immediately apparent, while sustainability is manifested in many ways. Tulipwood is one of the most abundant US hardwoods. It accounts for nearly 8% of US forests' wood volume and grows at a rate of 35 million m³ a year, with an average annual harvest of 17 million m³. The stairs are built from standard elements, creating as little waste as possible, and the structure is designed to be reused, either in part or as a whole.

Added to this, AHEC has used Endless Stair to build on its LCA of US hardwoods, carried out by PE International. The sustainability consultant has now produced an 'i-report' modelling system that measures all the processes of the Endless Stair, as well as for the impacts of 1m³ of CLT tulipwood.

CLT is typically made from softwood but using hardwood, with its greater strength properties, requires less material and the project team agree that this sculpture demonstrates the real potential for tulipwood.

"This is going to open up new boundaries," said Chad Cole of Imola Legno, the Italian company which manufactured the CLT. "We can do the same type of applications but using less material than if we were using softwood. This is using the resource in a much more sustainable way and it opens new avenues for architects."

Alex de Rijke, director of dRMM, described wood as "the new concrete" and suggested that, just as the 19th century had belonged to steel construction and the 20th to concrete, the 21st century would be timber.

"There's hope in timber construction that you can't ascribe to steel or concrete because of their high embodied CO2," he said.

He added that dRMM had "distanced" itself from hardwoods because of the perceived illegality and sustainability risks, but discussions with AHEC had convinced the practice otherwise.

And of course the LCA can communicate this to other architects and designers.

Adrian Campbell of Arup said that now tulipwood CLT had been proven, the potential was enormous. "The application is now down to the limitlessness of imagination, and the design profession is great at coming up with solutions," he said.

Now AHEC is hoping the Endless Stair will persuade even more architects of hardwoods' potential in construction.

There's no doubt that its message has already reached a wide audience. Among the hundreds of people who explored and climbed the Endless Stair during the first weekend it opened were six Cybermen and a wedding party which used it as a backdrop to photos - and no doubt there were some architects and engineers among those visitors too.

Endless Stair is open every day from 9am to dusk until October 10.

Endless Stair finite facts

  • A total of 11.4 tonnes of tulipwood is used in the finished sculpture.
  • The panels are created from three layers of 20mm timber.
  • The total length of all the panels is 436m - 4.5 times the height of Big Ben.
  • There are 187 steps. The shortest route to the top is 48 steps.
  • Arup estimates that a maximum of 93 people will be on the Endless Stair at any one time.

The CLT tulipwood Endless Stair provides views along the Thames Photo: Alex De Rijke
Photo: Thomas Etchells