Engineered timber structures are growing taller and bolder as technology adds strength to lightness –and the economics are adding up too. Industry experts gathered to assess progress
Timber is having its moment. For timber engineers working today such is the pace of innovation and change in the sector that excitement compares to that of steel engineers in downtown Chicago at the turn of the 20th century. Timber engineering is gaining momentum – tall buildings are being erected at speed worldwide using engineered timber products, many prefabricated off-site and modular.
Recently we’ve seen the eight-storey pure engineered timber Puukuokka Housing by OOPEAA in Finland, and UK trailblazers like Waugh Thistleton’s Murray Grove. And what of PLP Architecture’s 300m timber ‘Toothpick’ for Barbican? Cross laminated timber (CLT) can reach 13 storeys, and more when used with steel, concrete or laminated veneer lumber (LVL). In fact, pure LVL can go higher. These are not dizzying heights, but there are other innovations – such as the double-curvature Lister Mills rooftop extension in Bradford by Jennifer Juritz at David Morley Architects, made possible by the material’s relative light weight. Finnish timber manufacturer Metsä Wood teamed up with RIBA Journal at the end of March to discuss with the industry’s experts engineered timber’s progress and evolving possibilities.
So where is engineered timber now? Over the past couple of decades technology has transformed timber from a one-to-four storey stick-build structural product into one that can be used for tall buildings. Yet, as ever, with a large array of experts around the table, there was some dispute about how far it had come and what could be achieved.
‘Beyond 13 storeys we need a structural frame,’ said Nick Milestone of B & K Structures, ‘Either steel, concrete or glulam to stop the risk of the building blowing away. But there’s potential with Metsä to put the stronger LVL in the centre of CLT to give the additional storeys.’
Anthony Thistleton, however, thought designers could use crafty design – like flaring buildings out at the bottom to give natural stability, or using massive steel anchors such as at Dalston Lane – to make engineered timber reach 20 storeys. At Dalston Lane, the building needed to be light as it was above the Eurostar tracks. ‘An engineered timber frame is typically one-fifth the weight of a concrete one,’ he said.
Opportunities are apparent in all buildings, with LVL and CLT considered a great product for floorplates, wall panels, service risers and a host of other things. Hawkins\Brown’s Wenlock Cross in London was cited as a building that could have been unlimited in height because of its steel structure with engineered timber floors and walls. And Linda Thiel of Sweden’s White Arkitekter said timber there is being used for commercial and public buildings as well as houses, but wouldn’t have been in the past.
Once designers see engineered timber as a different material, true design will flourish and expand in a new architecture
All agreed the potential was enormous, with Tim Lucas of Price & Myers convinced that once engineers find better ways to finely glue timber materials together it would really fly.
‘It’s very early days for this technology: LVL, CLT and all the others are really very young,’ said Mike Kane, director of KMK Architects and senior lecturer at South Bank University. ‘Students in universities are getting to grips with it, and see it as an opportunity to do something different from the old guys. People call it the new concrete, but that’s kind of an understatement.’
The problem for many around the table in terms of design was that too often engineered timber is being used simply to replace concrete. Once designers see it as a different material, design will flourish and create a new architecture. Thiel thought part of that process required designers to start with how to put buildings together, rather than working from a design and then trying to figure out how to build it.
Yet, while the use of engineered timber products is growing, it is not widespread, with the rest of the industry slower to take up the products than architects are. Frank Werling of Metsä Wood said: ‘Architects have no problem designing in timber but it is difficult to find enough structural engineers that can do it. There are firms – Engenuiti, Ramboll, Price Myers – but the wider market reverts to steel as soon as something doesn’t work in standard CLS beam size.’
This affects the whole industry and has led to specialisation, pricing-in risk (making it more expensive), and sceptical developers. As Rory Bergin of HTA Design explained: ‘We find there is still a lot of anxiety and lack of knowledge, particularly on cost.’
Although not all participants agreed that building engineered timber buildings was more expensive – with Thistleton saying that Dalston Lane’s CLT frame cost £185/m², on a par with concrete at £175/m²,
– cost was the defining deterrent. Participations mostly saw this as blinkered, agreeing that it was not that they needed convincing but that the methods of measuring the total cost of a building have not yet adapted to take into account the broader benefits of timber products. These are currently invisible in the industry’s short-termist measurements, especially in terms of the health and wellbeing of occupants after delivery, or just the simple procurement and time savings.
Overwhelmingly the panel felt there was a need to promote the topic more and gather intelligence. It’s happening, but slowly.
‘The people we need to convince,’ suggested Milestone, ‘are quantity surveyors. I’m starting to see that now with firms like Gardiner & Theobold which is measuring the costs of engineered timber against traditional construction and going to developers saying they can now build it quicker, lighter and cheaper. It is now a competitive solution. Reinforce Concrete frame is becoming very expensive.’
The way to further innovation is to ‘push at the sweet spots’ where the benefits are indisputable to the client
In the meanwhile, Bergin at HTA believed the way to further innovation was to ‘push at the sweet spots’ where the benefits are indisputable to the client: those in a hurry doing hotels or student and rental accommodation.
‘There’s an economic benefit to these types of clients. They can go from delivering three projects to five over a 10-year period. At that point the question of whether engineered timber is more expensive simply disappears.’ In the long run, ensuring a reasonable uptake among such clients will create economies of scale for architects to then go after, for example, the housebuilders. On the other hand, Alex Smith of Hawkins\Brown saw engineered timber as a great structural product for schools because of the bigger spaces it permits.
The green, speed and light advantages, on top of creating a new environmental agenda to architecture, overcome fire and waterproofing concerns. There are simple solutions too – for example that services are kept separate from structure. It was not felt Building Regulations had kept engineered timber niche, quite the opposite: Werling believes ‘they are some of the most liberal’. Rather, it is about generating knowledge and information – and convincing insurers there is less risk than they think.
What architects want from the sector is standard detailing and tools provided by manufacturers (started recently with the Structural Timber Association guide), consistent information tackling life carbon measurements, and more joined up professional bodies promoting timber products. Right now the timber industry is fragmented as compared with steel and concrete. That automatically makes competing more challenging, with different members in different groups that don’t necessarily talk. ‘Ultimately they will get together,’ summarised Milestone, who is also chairman of the Timber Research and Development Association (TRADA). Inspiration could come from Sweden, where academia has teamed up with housebuilders and architects contribute to external R&D budgets, as well as from Germany which is dominated by prefab timber frame. But that takes time, and we are only at the beginning.
Nigel Ostime project delivery director, Hawkins\Brown (chair)
Frank Werling head of technical, engineering and design, Metsä Wood
Alex Smith project architect, Hawkins\Brown
Linda Thiel architect, White Arkitekter
Rory Bergin partner, sustainable futures, HTA
Anthony Thistleton director and founder, Waugh Thistleton
Tim Lucas partner, Price & Myers
Jennifer Juritz associate, David Morley Architects
Tom Dollard associate and head of sustainable design, Pollard Thomas Edwards
Mike Kane director, KMK Architects and senior lecturer at South Bank University
Nick Milestone managing director, B & K Structures
Joanna Marshal marketing manager, Metsä Wood
Henni Rousu marketing manager, Metsä Wood
Mikko Saavalainen senior vice president, business development, Metsä Wood