A dramatic structure is going to sit in the courtyard of Chelsea College of Art, almost opposite Tate Britain, for the London Design Festival. Made of timber, the structure, effectively a beam curving up at both ends, is called The Smile and looks just like one. Cheerful in form, it should also bring a smile to visitors’ faces. In fact, many will consider it one of the most exciting installations of the festival.
But David Venables, European director of the American Hardwood Export Council and initiator of the project, is clear that in his terms it is not an installation at all, but something far more important. ‘It’s meant to represent the challenges of a building,’ he said.
The Smile is designed by architect Alison Brooks and engineer Arup, using tulipwood CLT (cross-laminated timber). Tulipwood is an abundant, lightweight but strong hardwood, and The Smile is the culmination of an effort by AHEC to show that it can have a structural use in buildings. While CLT is becoming a widely accepted means of building around the world, it has been done exclusively in softwood so far. AHEC has been experimenting with tulipwood, most particularly in the design and making of the Endless Stair, a project for the London Design Festival two years ago, designed by architect dRMM with Arup as engineer.
‘We learnt so much from the Endless Stair that we were able to take it forward to industrial production,’ David Venables explained. Whereas the Endless Stair used tulipwood CLT that had been prototyped for the occasion in a kind of hand-crafting approach, The Smile is being made by German company Zueblin using a real manufacturing process that is an adaptation of the way that it makes softwood CLT commercially.
‘Rather than doing our experimentation in a laboratory, we do it in public,’ Venables said. ‘It is risky but the rewards are great. As a result of the Endless Stair, debate has gone on all over Europe about hardwood CLT. ‘
Since softwood CLT is such a successful product, and one with a growing market, why is Venables so keen to propose an alternative? The answer is that he is aware that there are niches where a higher-quality product will win out – where the greater strength or improved appearance of hardwood CLT will make it the material of choice, and quite possibly the only solution.
‘The bulk of the market is decided on cost,’ Venables explained. ‘So using European softwood makes sense. But there are requirements for more specialised solutions – for instance in public buildings, or in lower cost affordable housing, and that is where we may have an opportunity.
‘The brief for this project was that all experimentation with CLT has no meaning unless it becomes something that industry can embrace and present as a solution for architects and engineers. ‘ Zueblin, the manufacturer of the CLT for The Smile, has a reputation for specialist one-off projects, and the way that it makes its CLT is different from the approach of other manufacturers. It uses a vacuum bag to create the multi-layer material rather than the pressurised plate approach that is most common. This allows it to create, for example, curved elements and to work with smaller quantities – both essential for the CLT for The Smile.
Nevertheless, Venables stresses, ‘It’s a large industrial product so it’s not refined. We learnt so much when we were doing the Endless Stair that we were able to take it to industrial production.’ He is very excited by the fact that, in parallel to this project, Zueblin is also making tulipwood CLT panels for a live building project where they will have a permanent life –a project where architect, engineer and client have opted for the material because it is the best and most effective solution and not ‘merely’ because it is interesting.
For Venables the work on tulipwood CLT is vital because it is good both for the American hardwood producers and for the environment. In order to use timber in the most environmentally friendly way, it is vital to use as much as possible of what is grown and harvested –to throw away as little as possible. There is a double win for tulipwood CLT. First the timber is abundant, naturally representing a large proportion of hardwood forests. And secondly, CLT uses the lowest grades of the timber – grades that are no longer exported for furniture production and so would otherwise have a very restricted market.
While using these previously unloved grades is evidently good for the environment, it is also good for the producers, who are seeing a potential new market. And as a result, they have been very supportive of The Smile, providing three or four truck-loads of material to the manufacturer for free. ‘They can see that it has potential,’ Venables said.
The point about The Smile is not just that it showcases the use of hardwood CLT, but that it makes the elements work as hard as they possibly can. It is a massive challenge in terms of scale and engineering as well as a demonstration of just how exciting and beautiful a building using CLT can be. ‘Why wouldn’t I do it on a public space in London?’ Venables asked. ‘If you are an engineer or architect you will look at it and probably understand how amazing it is.’
He added: ‘It’s the most challenging thing we have done to date purely becasue of the scale and the fact that we are asking everybody to do something that they have not done before. The team has been brilliant. It has felt more of a unit than ever. There has been a lot of sharing of ideas. I like the fact that they draw on our technical expertise for the material. These are serious companies giving up their time to follow through an idea because they believe in it.’
This has effectively been a 10-year project, but it is not the only way in which AHEC is challenging the way that hardwoods can be used. It is also = looking at producing glulam elements using American hardwoods. ‘We wanted to create further discussion and debate that widens opportunities for materials,’ Venables said.
The Smile is certainly doing that.