Where is CLT Going?

Cross Laminated Timber's breath-taking rise continues to accelerate as forward looking architects, cities and investors make it their material of choice.

Unstructured Extra takes stock of CLT on the cusp of going Global

The platform was crowded as the London bound train approached. At the end of a working day in October, the rush hour commuters waiting at Birmingham International Station, were joined by another stream of travellers - attendee's at the annual UK Construction Week jamboree, making their way home after a day on the floor of Birmingham's cavernous National Exhibition Centre. Beyond the three day Timber-Expo, a major construction industry, business, networking and showcasing event, off beyond the latest four wheel crane and drilling technology, was a smaller dedicated wing of the construction bash. Here, reps from companies from many parts of the world were standing, waiting by their stalls, introductory smiles at the ready, to respond to enquiries with the hope of UK business. The Austrians, Americans and French were there, though also a sizeable contingent from less well-known countries from the British timber industry; a Ghanese timber industry representation and, another surprise, a Belo-Russian stand. At a far end corner, up on a temporary stage, architects, engineers and other industry figures were being asked questions by the man from TRADA, one of the UK industries main timber hubs. A tall architect, in the all black uniform of the profession, was just winding up his presentation, running through a series of renders for their big timber project, the Forest Green football stadium, outside Stroud, Gloucestershire. The stadium was part of a dramatic development by one of Forest Green Rover's highest profile backers, Dale Vince. Vince was the one time new age traveller who founded the hippy wind energy company Ecotricity. After Vince became chair the aptly named Forest Green squad became the first professional league team to become fully vegan, entertainingly appropriate for a town, which is a prime candidate for eco-centric capital of the country. Now, here was another move, an eco-friendly stadium designed by one of the premier division UK celebrity practices. Looking up at the renders on the screen made for enticing eye candy, though the more dramatic story was that the architect was from Zaha Hadid, one of the UK's best-known starchitect studios, known for biomorphic curves and flowing lines, but not for timber. They had been chosen, even though several of the other finalists with much deeper sustainability reputations - were shortlisted. These were also much smaller practices, with zero recognition. But here was yet another high-profile starchitect studio making a concerted move into CLT and engineered timber, in the bucolic Cotswolds valley town of Nailsworth.

There, on the station platform, two thoughts were preoccupying me. The first was how the National Exhibition Centre was almost the exact opposite of what a new showcase timber eco-conference centre could be, and secondly how the Hadid architect, Jim Heverin, had seemed defensive when, during questions immediately after his presentation, I’d asked, admittedly provocatively, whether Hadid wasn’t coming rather late to the timber party, replying that, “It doesn’t need to be a race.” After the session was finished we exchanged contact details, leaving me to wonder if he’d get back to me when I mailed him – he did, belatedly and then a third very obvious thought popped into my head. Surely the station I was in, Birmingham International slated to be one of the new major junctions on High Speed 2, would be in the running for a spectacular engineered timber make-over. Once the announcements, publicity and accompanying whizzy renders about winning station designs appeared in the next year. Just look at what Fosters had done at Canada Water. And what if Zaha Hadid Architects, if were on one of the bidding consortia, were awarded the Birmingham International station? Apparently my thoughts were on the slow train. I should have connected the HS2 stations to the engineered timber revolution months, if not years earlier. By the time I’d found my seat on the train, the notion of a joint station-NEC timber showcase had stolen into my imagination.

Like any number of other practices working on timber projects across Europe, and the planet, Hadid’s choice is another sign of the CLT rush currently underway, in Europe, and across much of the planet. Above the ambient noise, those working in this relatively recondite field are watching as the sweep and momentum of this revolution gathers pace. There are practices who wouldn’t have been seen dead using CLT ten, or even five years, ago, now sticking their toes in the water, and ensuring that their professional knowledge base gets up to speed and prepared for taking on a growing workload of timber based projects.

All over Europe – and indeed various parts of the planet - there is talk of new CLT factories opening. CPD’s are being convened, conferences multiplying. A groundswell of new CLT projects, both large and small, are starting and being completed. In countries hitherto not traditionally known for timber, Denmark and Holland – see the brick countries CLT piece here - as the legal requirements of Paris Climate Change agreements requiring architects to meet new, more challenging sustainability briefs begin to bite. CLT is getting more attention and showcase projects are appearing, 650, 000 of CLT was manufactured in 2016, an estimated 770 000 tonnes in 2017 year, with confident predictions of 1 million tonnes either this year or 2019. The vast majority of this increase has been on European ground, but possibly the most consequential news is the growth of engineered timber and CLT projects and production across the rest of the world.

The rise of popularity for CLT has appeared after a mere 24 years since the first CLT building was constructed, and 22 years after the first multi-storey housing block was completed. The three-storey building, designed by Karl Moser, is often cited as the ground zero of CLT and stands in the small Bavarian town of Aichach, near the one time Merk Factory, which prepared the CLT. Three years later, in 1997 KLH launched CLT commercially, after further test experiments. Although other countries from the two European timber power-houses, the Northern Nordic countries (Norway, Sweden and Finland), and the Alpine DACH group, (Germany, Austria and Switzerland) have been part of the development, the CLT story is really an Austrian one. It is Austrian – primarily spruce – forests, from which the vast majority of CLT buildings have been built. Likewise the main factories are in Austria, and as the online Timber Online website recently reported, 60% of European production originates from within a 100 km radius of South East Austria. Locating the radius centre in the ski resort of Obertauern, Timber Net calculated that 408,000 m³ CLT was manufactured from within this forested circle, where Stora Enso, Binderholz and KLH, the three largest CLT manufacturers, can be found.

This South East Austrian dominance is in the midst of changing, a two-part shift, in which CLT production is spreading across Europe, and also increasing internationally. European CLT production is anticipated to double in volume by 2020. Setting up a CLT factory doesn’t come cheap, and the swathe of new factories planned is an indication of investment confidence in the field. One recent report suggests the CLT market will be worth $2.07 billion by 2025. Indeed, the seemingly weekly news about new CLT factories opening has become part of the rush story. The increasing production levels look set to continue, both anticipating and feeding the exponential increase in demand for the material. According to Professor Gerhard Schickhofer - see Schickhofer interview feature here - at Graz Technical University’s Institute of Timber Engineering and Wood Technology  there were 29 factories in 2016, 32 in 2017, and an anticipated 37 by the end of this year. While smaller, the rest of the world figures point in the same growth direction; 15 factories in 2016, 16 last year and 17 this year.

Take for instance, Stora Enso. In mid-2017 the Finnish timber industry giant announced a dedicated new factory in mid-Sweden as part of a wider strategic move into building materials. This signalled the direction of travel: industry watchers took notice when a year earlier the company committed $900 million for new factories and production facilities in Guanxi Province China. Even if CLT isn’t dropping off the end of conveyer belts in Southern China just yet, this is another investment sending ripples through the timber sector.

Look at the Non-European regions where the wider uptake is happening, and it remains, at least at present, a widely Western phenomena. Much of the growth is in forested softwood regions of the world, such as North America, though New Zealand, where the first southern hemisphere manufacturer, XLam New Zealand, started production in Nelson and last year expanded into Australia with a second factory. Japan, which began developing a domestic CLT industry after the 2010 Tsunami disaster, rewrote the sustainability agenda and policy, and already has six factories producing 60,000 m³, with a seventh opening this year, ahead of its goal of 500,000m³ production by 2024. There are smaller facilities in Italy, Spain and some of the Baltic and eastern middle European countries, Latvia, Estonia, and Czech Republic. The Segezha Timber group announced opening the first Russian CLT factory in the far western Karolian region, which crosses over into Eastern Finland. Vast tracts, indeed the vast majority of countries on the planet aren’t part of these shifts in building materials, although CLT is on the agenda of the United Nations Environmental Programme (UNEP), and a variety of European agencies who work to develop international business are busy promoting the potential of the material. The Dutch Government’s Centre for the Promotion of Imports for the developing countries (CBI) produced a report outlining the potential of African countries hoping to develop CLT production in the Tropics. This, of course, would be hardwood, and the possible huge potential for hardwood hasn’t escaped the various relevant organisations, although R&D into hardwood CLT is only just beginning. The American Hardwood Export Council (AHEC), a US Department of Agriculture group funded by hardwood timber promotion agencies has probably done the most so far to advance hardwood CLT, with a range of research experiments to test the structural potential taking place over the last five or so years in Britain – see the Maggies Centre feature.

The breadth of the CLT take off makes the current moment historic in significance. The current second half of the decade, so the argument runs, will be seen as the years that CLT not only became a mainstream building material, but began a new chapter, moving from a regional European, and principally Alpine environment, to something more international. CLT will be used in buildings in different parts of the world. If this is the case, it is because CLT responds to questions, primarily about sustainability, though also ease and speed of construction, which have only become more pressing with each passing year.

The mantra around engineered timber, not least CLT, is that it is a much more radical and sustainable material than concrete, steel and brick, the primary building materials for buildings  throughout the 20th century, and indeed since the Industrial revolution. Timber is a natural material, this line of thinking continues, and grows back, meaning the source can always be replenished. CLT panels are thick prefabricated pieces of glued timber laid cross-ways on top of each other, sandwich like, and compressed to make for super-strong weight bearing units which can support vast towering buildings in ways similar to the promise of steel and concrete when first used as structural building materials. Not only this, but using CLT panels, in combination with other engineered timbers, or in hybrid form with concrete, means buildings can be up to 20% lighter, and can be built faster, and with other benefits, such as the relative quietness of construction, the absence of wet trades, and the ease with which the panels can be prepared as prefabricated modular sections. Digital technologies have played a sizeable part in the rise of the CLT. The CNC router enables one-off customised designs easily, while the internet allows architects to send designs all across the world to whatever production facility they’re working with.

The consensus is that CLT will be used principally in housing and office buildings, particularly of mid-scale height - between four to eight or so storeys, replacing or working with 20th century concrete, steel and brick. Carbon energy footprints will drop considerably, as embodied energy takes up more of a buildings’ footprint in relation to the increased operational efficiencies. This is easily imagined in the developed West, Europe and North America, as there is a broader need for sustainable housing on a rapidly urbanising planet. Over half the planet’s 7.6 billion are now living in megacities, cities, and other urban areas, and both the curve and the world’s population is set to grow over the next decades. UN Habitat forecast 9 billion total global population by 2030, of which 60% will be urbanised, rising by mid-century, to 70%. Alongside this unprecedented transition there are the twin challenges of climate change and resource depletion. A consensus among urban planning experts has emphasised compact city thinking, focused on building up; dense and high-rise. But the need for far smarter energy uses and footprints hits something of a wall when you realise concrete is the fourth single largest carbon emitter, with between 7% and 11% (depending on where you go looking for your figures,) of the world’s entire carbon emissions. Steel, too, isn’t exactly carbon neutral, and, down the line, there’s also a Peak-Metal scenario visible on the horizon. Where, the question is asked rhetorically, will the materials come from in both the developing and developed world for future urban housing, including high-rise?

CLT’s arrival, along with ever increasing numbers of medium and increasingly high, medium high rises, provides a critical answer for those who have been posing the question. If forests have been the answer to many of the green questions, now this next green contribution can come into its own. The sea change has drawn both those old and new to sustainable urban design into open CLT advocacy, drawing together such diverse bedfellows as the American Eco-city guru, Richard Register to the London borough of Hackney councillors, UN agencies, or for that matter a starchitect practice such as Zaha Hadid.

The factories’ growing levels of production speaks for itself in terms of the amount of buildings, which could be described as CLT buildings, or ones which use a significant amount of the material. The most visible example of this increase in CLT at the moment is the timber towers’ race. Six years ago, one Canadian commentator’s wrote of “a megabuzz about tall timber right now.” At the time I thought that was hyperbole, but six years later, like it or not, it is clear he was merely ahead of himself. This competition for the ever yet taller timber mid or high rise has taken off with various cities in many of the more forested parts of the world, from Vienna to Vancouver, New Zealand to Norway, all looking to build tall and high.

When the Japanese architect, Shigeru Ban, completes his 73 metre high Terrace House, towering over Coal Harbour’s high end marina district in Vancouver, BC, the building will replace the world’s current tallest completed hybrid timber-concrete building, just a few miles away. The current holder of the title is ActonOstry Architects Brock Commons’ student accommodation on the University of British Columbia campus. At 18 storey's high (53m), Brock Commons pipped Bergen’s Treet (or Tree) tower by 0.2 which is 52.8 metres becoming the tallest hybrid tower in the world when it was completed in 2014.  The timber tower race shows no signs of slackening off; Vienna’s 24 storey HoHo Project, by Rüdiger Lainer + Partner will, when complete, outstrip both of the previous record-breaking towers. Other towers are also rising that will reach similar levels to HoHo – for an overview, see this edition’s Further section. In Stockholm  (CF Moller’s Woodscraper) Norway, Mjosa 80 metres Voll Arkitekter and in no-wood Netherlands, Amsterdam will see the 73m HAUT tower complete in 2020. By that time a new tranche of yet taller towers will be making the news. Not unrelated motives must be suspected with the collaborative Smith & Wallwork engineers. PLP Architecture and Cambridge University’s 80m storey Oakwood Tower standing high above London’s Barbican centre, designed to bring on gasps of shock and awe when the images were released in 2015 - though you needed to read the small print: for the time-being the plan  was strictly conceptual. Likewise the teams’ more recent collaborative effort, the 35 storey Tall Timber 2 designed this time for the Dutch city of Provast, reaches an extra 45 to 125 metres. Projects like these have upped the timber ante, however unlikely their real world applications.

Smaller in scale, but much closer to home, demonstrating another face of the scale of ambition in the CLT rush is, the modular prefabricated factories in Britain, yet another sign of CLT’s mainstream take off. In less well known Sherburn-Le-Elmet, 15 miles east of Leeds, Europe’s largest CLT factory is up and running. Set up by insurance giant, Legal & General in 2016 with the title, Legal & General Modular, the factory’s opening sends another ramping up of CLT based manufacturing. The factory includes a dedicated lamination plant, CNC production and 12 production lines. Once fully operational the aim is for 3000 pre-fabricated CLT modular buildings rolling out annually. Already in the early stages of production, early prefabricated modular designs have been developed by various architects, including the UK’s CLT pioneers WaughThistleton – see WaughThistleton and Hackney piece here, Sarah Wigglesworth Architects and South London's Wimshurst-Pelleriti Architects. The latter’s prototype Launch Pod was the first project off the production line in June 2017. The first commercial prefab buildings for Richmond Housing Partnership are arriving, if things go according to plan, in the summer of 2018.  For WaughThistleton’s Andrew Waugh the factory is a real game changer. Waugh says, “L&G have given the notion of CLT as cost efficient a massive boost. … They are able to demonstrate a building on a stunningly large scale, which requires significant investment, and technical research. It is a significant move.”

Many people across the spectrum of architects and builders are watching Legal & General’s dramatic investment in CLT modular housing. Observers are watching this big move to see whether the start-up goes according to plan, with varying degrees of confidence and scepticism, ranging from whether and how quickly the rate of production will meet the 3000 target, to whether the apparent commitment to use locally sourced timber (Scotland is really the only foreseeable option) will amount to more than airy promotional puffery. L&G hardly have a monopoly on modular systems, such systems can be found across the factory infrastructure. One of the largest are the 100% modular box units developed by Kaufmann Bausystem’s and produced at the MM-G Factory in Leoben, for large scale, if not high rise projects, like SaubrauchHutton’s recent Hamburg Universal Design Quartier project – see SauerbrauchHutton Hamburg feature.

Both the wave of high rise projects and the arrival of modular housing have received different though related criticism from different parties involved in CLT. Graz’s professor Schickhofer is plain-spoken, claiming that the tall tower brigade are missing the point, and the focus should be on new timber construction systems, which is not what timber towers are doing: "The objective should not be to build even more storeys but increasing the building’s operating life as well as exploring a broader range of applications," he told Timber On-Line. dRMM’s Alex de Rijke, – see de Rijke’s timber towers critique feature -, one of the UK’s architectural pioneers of CLT is blunter; “I think building tall in timber isn’t necessarily about timber, it’s more about a boy-scout mentality…. Sometimes it’s more important to think about what makes a good city, than to think we have to build the highest timber tower. I personally think there is no need”. He continues, by arguing that it is ‘structurally perverse’, that despite ‘amazing’ properties to force the towers to go ever higher, “just to get that boy-scout badge of honour for the highest timber building is just to get it to go higher. This is, I think, just naval gazing…”

Andrew Waugh, whose north London studio built what is generally considered the first CLT timber tower, Murray Grove – for a detailed overview of WaughThistleton Hackney piece - concurs, observing that the priority is for timber to be taken seriously, that “it isn’t just fashion”. Architects and engineers need to develop their knowledge an expertise regarding timber’s properties, where to use it appropriately, and to understand that CLT is only one of the family of engineered timbers that can be used together, or with other materials.

The most persuasive argument I’ve come across against high-rise - in general - was research carried out by Jan Gehl Architects, the respected Copenhagen practice and urban designers. They realised that children, as well as the elderly, socially isolated, and others living above the first three floors of high rise were much less likely to use the ground-level outdoors than those living at three floors or lower in a tower block. The consequence is less connection with daily urban life, and for the children, fewer friends. But this isn’t an argument against timber towers as such. Realism requires us to acknowledge that soon there will be more than 8 or 9 million people on this planet, crowding into cities and other urban areas, contending with both increasingly scarce resources  and carbon mitigation. The pragmatism of the head must trump the social poetry of the heart. Tall timber, the realist admits, is here to stay.

Still, across the small but growing CLT network, a sizeable constituency can be found at the edges of the more committed practitioners, which believes that the race to the top is a rather sizeable diversion, distraction even. Timber’s real 21st century future lies elsewhere.

What many architects and engineers share, however, is a fascination for systems, be it building systems, idea systems, or systems of technology, and in this respect, the off-the-industrial-shelf elegance of the factory production line, the modular prefabricated buildings, fascinate many architects.  The factory is only one part of digital manufacture there is also volumetric design and BIM, a system sitting within a broader systemic shift from Design for Construction (DfC) to Design for Manufacture (DfM.)

Architects and engineers are also often concerned with performance, efficiency, and whether a design arrives at the most technically elegant solutions. Those who gravitate to these considerations are likely to dislike waste. Indeed, a significant drive for sustainability is with practitioners absorbed by these questions. CLT returns again and again to waste and efficiency questions. This is because CLT panels generally use up considerably more timber than they are required to technically; there is considerable redundancy in the engineered timber technology; chunks of the panels aren’t actually needed to keep the structure safe and standing. Some architects, like the Norwegian practice Helen & Hard, have been talking and taking steps to move ‘beyond CLT’ by designing out excess, and developing other systems. This is also influencing the moves toward CLT projects designed in combination with other engineered timbers, a rationale for the background rise in interest and use of laminated veneer lumber (LVL) which neither uses so much wood in manufacture, nor requires so much when specified in designing projects. For StoraEnso, their production of both CLT and LVL at different Finnish factories, is a distinct advantage, which they have made a cornerstone of their involvement in the Helsinki Wood City showcase, designed by the young Anttinen Oiva Architects. Similarly WaughThistleton are increasingly looking to hybrid timber approaches. A first example is their recent Vitsoe Production Centre in Leamington Spa, where hardwood birch product from Germany called Baubuche has been specified, which, because of its strength, doesn’t require the same amount of glulam or CLT, reducing the total timber needed, or in the words of their publicity “offering greater elegance to the timber structure.” de Rijke’s ongoing experiments with American tulipwood is premised on the same principle, less hardwood is needed to carry a structure, than softwood, meaning slimmer, lighter walls, a clear feature in evidence at the Oldham Maggies. There are other material technology’s appearing on the market, such as Korlam, which demonstrate new performance capabilities using less timber. And then there is the question of glues, which are used in all engineered timbers. While the polyurethane glues used are certified for their relatively low pollution and toxic properties, they don’t fully resolve the issue in the way wood dowel approaches such as Brettstapel solid panels do – see here for an in-depth exploration of Brettstapel – a dimension engineered timber companies more or less ignore.

As it is, questions of waste and efficiency are all very well, but pale next to the challenge of what happens if the wood runs out. Or rather, what happens if accredited sustainably grown woods reach capacity. This is a real prospect and is becoming a concern, and is increasingly discussed openly. Never mind, that, as one Finnish architect told me some years ago, “the Finnish forests produce enough new wood for the country’s complete building needs every 10 hours,” the forests that all these new factories will be getting their raw wood from aren’t infinite. This is particularly the case for Europe, even if there isn’t a complete absence of forests as one moves further eastwards into and through Russia. The sources and forms of production are the questions of concern.  Both major – and smaller – companies make guarantees about the provenance of their timber. StoraEnso promise to plant a tree for every one used in the production processes. It is anticipated that with the number of factories starting up, production will double by 2020. People are saying that only a couple of years later it will be necessary to use timber very carefully and efficiently with attention to replacement. Still, the Austrian factories are apparently finding new forest stands. For example, a new factory producing 50, 000 m tonnes a year has been announced for West Austria, outside the production region Styrian heartland. It’s in this context that the rationale for hardwood CLT comes to the fore, and since the USA contains vast tracts of unused tulipwood it comes as no surprise that AHEC’s next research project is likely to push the next phase of Tulipwood CLT R&D into housing.

The issue of dwindling wood resources touches on a further question. Is the growth of CLT in buildings and architecture actually doing what the timber and building industries say it is doing, that is, radically reducing building footprints, delivering carbon neutral and even the fabled negative carbon buildings? The sustainable rationale for the increasing proportion of timber buildings is because mainstream, orthodox materials don’t adequately draw down footprints, a critical point given the carbon footprint of building is generally put at around 40%. Timber in construction is the archetypal embodiment of carbon stored in buildings, it’s used to signal green aspiration, and, the argument follows, engineered timber, including CLT, stores carbon in the structural body of a building. Many CLT projects, and all showcases, make a big issue of the amount of carbon being saved or stored by the use of timber. The first timber tower, Murray Grove, saved 306 carbon tonnes in 2009. Last year Vancouver’s Brock Commons, the architects say, saves 2432 carbon tonnes through using CLT and other wood products. This may sound impressive, yet, in Britain and elsewhere, there’s a growing body of evidence that the construction sector’s carbon footprint has not fundamentally changed over the last twenty years. Research conducted by the University of Bath described a performance gap between the anticipated and actual footprints but was completely ignored, although the press release claimed this was a scandal worthy of the Volkswagen diesel controversy. Meanwhile, in more measured language, Parliament’s Committee on Climate Change reported scant downward movement in the proportion of carbon footprint attributable to buildings, in relation to Britain’s efforts to reduce its total carbon footprint by 80% by 2050. As it is, eco-footprinting, or carbon profiling remains a young science, and the statistics are considered as rough guiding figures rather than precise measurements.

This may not be an argument to lay at the engineered timber end of the construction industry, timber is likely still the most persuasive way of drawing down the built environment’s total carbon and energy footprints, but despite the mass of data about the amounts of CLT production, there appears to be very little on how those annual figures divide up into buildings, let alone breaking the figures down to distinguish the contribution of CLT and other wood materials in relation to different types of footprints,  for instance, by country or housing. Despite the proliferation of CLT projects there’s no sense of whether the materials uses are making any substantive difference in the carbon equation, which is generally cited as being at the heart of the case for CLT’s development.

One obvious and easy explanation is that the timber industry, while willing and happy to go along with sustainability when it suits them, won’t, if business plans bottom lines don’t add up, go the full distance required to be fully sustainable. Every timber company’s website and promotional material may boast and brag about how environmentally friendly their industry is, but the whole thrust is towards increasing production growth and therefore the harvesting of stands. This may be a rather crude characterisation – and a massive generalisation - but industrial forestry is a competitive business, raw in tooth and nail. A contrasting perspective is that some of these company’s are at the edge of a much bigger transformation, the arrival of Forest Industry 4.0, and the bio economy. Look again at the Swedish-Finnish timber giant, StoraEnso, who recently rebranded themselves as ‘The Renewable Materials Company.’ A key reason they, alongside the other big Nordic wood industry companies, have been developing construction materials for their portfolios is the collapse of paper and card, in the wake of the Internet and social media, which has been hugely disruptive, causing closures of mills in Finland. Repositioning themselves as companies at the heart of the new sustainable friendly bio economy, including the building sector, is part of these wider industry shifts. It’s also, however, to do with the advances in chemical and digital manipulation of wood at the microfibral and nano-scale. The emerging Forest Industry 4.0 vision foresees cars, planes and many other everyday things, which can be made from these transformed wood based renewable materials.  This is some way off, as are even more exotic dreams, for instance, programmable wood. At present bio-materials have advanced as far bio-composite granules, developed for, first off, bio-based spoons, forks and knives, and starting commercial production at one of StoraEnso’s Swedish paper mills by the summer. Seen in this light, CLT can be interpreted as an early expression of these Forest Industry 4.0 futures round the corner, though begging many questions regarding exactly what comes next.

As far as the broader construction industry is concerned, timber remains a small player amidst the larger canvas. Conventional wisdom suggests that the proportion of CLT construction, despite showing a dramatic increase, by comparison to the mainstream, remains minuscule, and that there is next to no impact. Certainly it is still very early days. In the recent Hackney Builds report on the North London borough that is often described as one of the centres of urban timber, and specifically CLT buildings, outlines all 26 timber buildings, of which 10 are small-ish residential units. This may be why the concrete producers do not – so far – treat timber as any kind of threat, even if mining companies such as BHP and Rio Tinto do task research analysts to observe the developments in the timber sector. Responding to a Reuters CLT high-rise feature enquiry, early in 2017, a spokesperson for LeFargeHolcim, the largest concrete manufacturer, said they only saw timbers rise as, at most, a marginal threat. 30 billion tonnes of concrete is used a year. But then, from small acorns do mighty engineered oaks grow.

Look around Europe, and it is clear that the CLT bandwagon is rolling on. Projects are increasing year after year, including many that are inspiring. It feels too early to say in relation to the carbon footprint, whether, and at what breaking point, this exponential increase will begin to make the difference that makes the difference. But as the numbers of CLT buildings multiply, CLT alone may not seem to be enough. The projects that are the most inspiring and thought provoking are the ones that use CLT as the core of the building fabric, but then take the building to another and different level of sustainability, generally in directions that have an impact at a social level, integrating lifestyle choices which also facilitate considerations of the energy and carbon footprints for individuals, groups, and on a  wider scale, carbon and energy footprints for society as a whole. Take for instance Patch22 in Amsterdam, an adaptable self-initiated seven-storey housing project on a piece of rundown industrial waterfront. A whole slew of extra ideas are housed within this CLT experiment, including entirely open and adaptable floor-space facilitated by the engineered timber open-span of each of the building’s floors. A further example is dRMM’s delicate, humane Maggie’s Oldham Centre, which opened last year. Or Helen & Hard’s co-housing project in Stavanger, Vindmøllebakken a forty-unit experiment in co-housing and shared living, with the strap line Gaining by Sharing. This buildingsits alongside the luminous Vennesla library, another more established form of social project. Or the startlingly ambitious Stream, one of the winning entrants in the French capital’s 2016 Reinventing Paris competition. Philippe Chiambaretta Architects (PCA) designed an entirely CLT and engineered timber building, sitting on an old bus station site, which provides the skeleton for a seven storey social experiment; including flexible shared live-work space, a local brewery and other biomimetic and ecosystem properties, like the 1200 metre roof-top vegetable gardens, from which families and office staff can grow vegetables and feed themselves. If it is built Stream will hopefully show how CLT and engineered timber can synergise with other sustainability features, which are going to be needed to drive down the carbon footprints. These are not huge timber towers in the sky, and they begin from buildings serving the social dimension.

There is a revolution going on in CLT and, as Andrew Waugh and others are often quoted as saying, it is the beginning of a new era in engineered timber, though the wider shape and form of the era needs to be borne in mind. The split between the large scale and the towering timbers beloved of developers the world over, and the smaller intimate and human scale, the ground on which synergies between social experiments and technical 21st century timber can be found, reflects social divides and expresses divergent paths about how people and different parts of society envision and imagine the future. Over the next years the built fabric landscape will surely continue to be populated by ever more CLT projects, a good thing. However, as the normalisation of CLT continues apace, while it may well turn out to be a small but critical contribution towards saving the planet, how far it’ll go in doing the same for humans is another question.