Arup’s timber specialist, Andrew Lawrence, may have taken a different tack in his career had it not been for the first project he worked on.
When he joined the international engineers as a graduate structural engineer in 1993, that first project was a Swiss art gallery designed by Renzo Piano.
"We were thinking of doing it in timber and I was excited by it. I loved the idea of working with a natural material that, to me, was a lot more interesting than steel or concrete," he said.
The project marked the start of Mr Lawrence’s specialisation in timber and it was fortunate timing because in the intervening 22 years, timber has developed from being a specialist material to a mainstream one.
"Virtually on every other project now we think about whether it would work in timber. It’s becoming a standard construction material for larger structures, alongside steel and concrete," said Mr Lawrence.
"With timber structures you can see how the members are built up from smaller pieces glued together and you can see how the connections fit together and that’s one of the reasons why people love timber structures so much."
And as an engineer, having your work on view is really rewarding.
"You feel you’ve been more involved in the architecture because the engineering literally becomes the architecture," he said.
While sustainability has been a major driver for specifying timber, Mr Lawrence believes its light weight and ability to be accurately machined are its biggest big selling points. He likens it to a giant IKEA shelf unit which fits together easily, thanks to the accurate computerised machining.
"There’s a big move towards precast concrete to avoid having wet trades on site but concrete cools and shrinks and no matter how hard you try, there’s a limit to how accurate you can make it. With timber, however, because it’s machined to high tolerances of +/-1mm it goes together much more easily on site."
Combine timber’s light weight and machining accuracy and you have another advantage: speed of construction. This has been an attraction for certain builds, such as schools, where one aim is as little disruption as possible, but Mr Lawrence believes that speed makes timber ideal for commercial buildings too.
"With an office you want to build it as fast as possible so you can start earning rental income, so using timber makes sense," he said – even, he added, when a timber structure is likely to cost more than concrete or steel.
"If you compare structural costs, timber will often be more expensive but when speed has a high value, that will completely overshadow the 2-3% extra in total building costs."
He believes that commercial buildings, where acoustic separation is less demanding than in residential multi-storey, are a natural home for timber. Arup has demonstrated this with the UK’s first all-timber four-storey commercial office building: BSkyB’s four-storey, glulam-framed Believe in Better Building in west London was completed in just 42 weeks.
Arup also delivered the neighbouring two-storey BSkyB Health and Fitness Centre, again with a glulam frame and CLT walls, but this time without spread of flame retardant.
"It saved the client about £85k in reduced flame coating but, more importantly, about two weeks on a very tight programme. It also helps with reuse or disposal at end of life," said Mr Lawrence.
Where timber really comes into its own is roofs, especially complex geometries where CNC machining enables it to achieve what other materials can’t; and relatively cheaply.
Timber’s strength-to-weight ratio and aesthetics are further plus points for roofs. "Weight for weight, timber is stronger than steel, so for a long-span roof it’s the most natural material to use," said Mr Lawrence.
"Also, generally the roof structure will be architecturally exposed so you see the beauty of the wood. You’re using all the advantages of the material: strong and light, not needing any finishes, and a warm appearance." Timber floor systems also offer potential, especially in tall steel-framed buildings.
"CLT can be a direct replacement for a wet concrete slab or metal deck. It’s about the same depth but it’s dry construction," said Mr Lawrence.
He also advocates greater use of composite products, such as timber concrete composite slabs. "They’re another addition to the family of timber options," he said.
Arup has plenty of examples of CNCmachined and engineered wood in its portfolio, starting about 10 years ago with the Serpentine Pavilion designed in conjunction with Alvaro Siza and made entirely from interlocking pieces of Kerto LVL.
"We had 459 component pieces and each one was different," said Mr Lawrence.
"Economically, I don’t think you could have achieved that in any other material, whereas with wood you just programme the CNC machine; it didn’t matter that there was no repetition."
The American red oak Timber Wave, erected outside the V&A for the London Design Festival 2011, also could not have been made in any other material.
"The same story carries through to the Pompidou-Metz where every piece was double curved and different and it carries through to the Metropol Parasol in Seville."
One of the latest projects is the visible timber gridshell roof of Crossrail Place, the first retail and public realm space to be created as part of the Crossrail network, which opened on May 1, 2015 at Canary Wharf.
The station roof is currently the longest timber roof in the UK but it will soon be overtaken by two more timber roofs Arup is working on. One is a timber gridshell roof for a Richard Rogers-designed Macallan whisky distillery and the other is the National Automotive Innovation Centre at Warwick University, designed by Cullinan Studio. The latter, which once completed will claim the prize for the UK’s largest timber roof, comprises around 40 15x15m panel bays.
"These are important statements for timber," said Mr Lawrence.
Arup was also involved in engineering the Endless Stair, the American Hardwood Export Council’s tulipwood CLT installation for the London Design Festival in 2013. This project was part of a developing interest in engineering under-used hardwoods, especially in applications where the timber is left exposed.
"Pollmeier is already producing beech LVL and that’s very cost competitive. It should be possible to make tulipwood CLT for a similar price to spruce CLT and we’re already talking to potential CLT manufacturers," he said.
While Mr Lawrence, who is a Wood Awards judge, is a timber fan, he does not, however, advocate a built environment entirely in timber.
"Some architects say we should use timber for everything and that will save all the world’s problems. I’m unable to agree with that," he said. "Every material has pros and cons – concrete is fantastic for foundations, steel is a great material. Timber is A.N. Other construction material which, for certain projects, makes a lot of sense."
While sustainability is a big selling point for timber it’s not enough on its own; cost is still king and the perceived price of timber can work against it.
"Most clients would like to be able to say their building is sustainable but even the greenest of organisations will rarely want to pay more for their structure," said Mr Lawrence.
A key part of creating a successful timber design is understanding the economics – and they’re more complicated than the formulaic costings per tonne for steel.
"It has to be economic and it has to compete with the steel or concrete options," said Mr Lawrence.
Connections are the most expensive element of a timber design, so having fewer connections reduces the cost, but solutions for acoustics, vibration and fire also add to the price. Taking a holistic approach to design is the most cost-effective approach.
This cost element is why Mr Lawrence believes that only half a dozen really tall all-timber buildings around the world will be completed.
"They’re exciting from an engineering point of view but a pure timber building at that height is not an economic solution," he said. "Once you get to that height you’re dominated by wind loading. You need tension connections to tie it to the ground and that’s where timber gets expensive and where its lightweight nature works against it."
Designing in timber requires an understanding of the material and these cost drivers and Mr Lawrence acknowledges that, even today, timber is given little coverage in degree courses. It is on-the-job training, however, that is really important and Arup is investings heavily in teaching its graduates and it aims to develop timber specialists in its offices around the world.
Mr Lawrence, who sits on the Eurocode committees, said the rewriting of Eurocode 5 to include CLT and timber/concrete composites will enable more timber construction, as will the new National Timber Specification, which he has worked on with TRADA.
"Having a National Specificiation for timber, as we already have for steel and concrete, will make it much easier for people to specify timber," he said.
He is also on the steering group producing TRADA’s new CLT handbook, a project that has encouraged manufacturers to collaborate more for mutual benefit.
"The timber industry has to work together to build the market overall. Clients don’t want to go to just one firm, they want multiple potential suppliers," said Mr Lawrence. "We want engineered timber as a commodity, just as concrete and steel are, and we’re starting to see that."
