Building With Wood is the Ultimate Carbon Capture Technology

Tim Smedley
Dec 9, 2019 · 8 min read

Name a carbon capture technology that is fully proven, used the world over, pumps out oxygen, and improves your wellbeing at the same time? There’s only one answer: trees. As trees grow they feed on carbon dioxide in the atmosphere and trap it in the form of wood: as long as the wood exists, the carbon is captured and not released back into the atmosphere. This makes wood not just carbon neutral, but carbon negative, as a building material.

When I met the architect Andrew Waugh earlier this year, on assignment for the BBC, I was struck by the simplicity of the solution he is proposing. Waugh likes to build with wood. As a young architect he used to be, he admits, something of a show-off, with a penchant for fast cars and sexy designs. Now he drives an unassuming electric car (think less Tesla, more hatchback) and builds functional, commercial tower blocks, out of wood. The reason is climate change. He wants wood to replace concrete and steel as the world’s primary building material, and in so doing grow more forests, and sequester more carbon.

Dalston Works, before its completion and brick cladding, in 2017. Credit: Waugh Thistleton Architects

“The [carbon capture and storage] machines being created for locking carbon in and burying are not as efficient as trees”, he enthuses. “Just grow more trees!”

So, let’s take a step back. Can wood really compete with concrete and steel? How is Waugh able to build tower blocks out of wood? And could this make a real difference to climate change?

Waugh took me to one of his completed buildings in East London: Dalston Works. It looks like an ordinary brick building, comprised of 121 apartments and 4,000 square metres of commercial space. Behind the brick facade, however, is an almost entirely timber building.

“We are over a train tunnel here”, he says, “so the [client] came to us because of lightweighting. We could deliver a 10-storey building on a site they thought they could only get 5 storeys [using traditional steel and concrete structures].” A reinforced concrete frame is 30% heavier than an equivalent wooden structure.

Dalston Works, East London, became the world’s largest CLT building in 2017. Credit: Daniel Shearing.

A wooden frame, however, couldn’t reach anywhere near 10 storeys if it was formed from single timber beams: timber, no matter how thickly cut, will warp with weathering and age. (The famous crooked spire of Chesterfield cathedral, England, is a good example). The technological breakthrough that Waugh is keen to show me (and the world — he was the first architect to use it to build a multi-storey tower) is cross-laminated timber, or CLT.

CLT is remarkably simple. Planks of wood, roughly one inch thick, are glued together in layers of three, the middle layer perpendicular to the others. This gives the wood weight-baring strength both horizontally and vertically, and means the CLT doesn’t warp; it now acts much like steel or reinforced concrete. Not only does this give the architect more options, it could also heal the planet. Concrete and steel are both hugely environmentally damaging to produce. Cement production alone, a key ingredient in concrete, is responsible for circa 8% of the world’s carbon emissions — more than the emissions of China. While the demand sand, another key ingredient, is increasingly unsustainable and devastating ecosystems.

A CLT interior mid-construction. All the walls, columns, floor and ceiling, are timber. Credit: Tim Crocker, Waugh Thistleton Architects.

“There’s only two tonnes of steel in this whole building”, says Waugh, as we gaze up at Dalston Works, “about the same as a VW van. All the internal [CLT] walls are structural. It is like a honeycomb — the parting walls and principle walls are made of [structural] CLT, about 4,000m3 of timber, 3,225 trees, housing 800 people, so about three trees per person in the building. That’s about the equivalent of 200 years of carbon savings [compared to a traditional concrete and steel construction].”

Of course, the benefits are only accrued if the forestry itself is sustainable. Across the world over 1 billion acres of forest is certified, with 16% of this having both PEFC and FSC certification. In Austrian and German forests alone, enough timber is grown within one hour to produce the CLT required for Dalston Works, which when completed was the largest timber building in the world. Crucially, demand for sustainable forestry doesn’t decrease forest cover, but increases it: supply must scale up in advance to meet demand. Thanks to having established forestry industries, Austria and Germany have around 48% and 32% forest cover respectively, amongst the largest in the EU.

Sustainable forestry in Germany. Photo by Jace & Afsoon on Unsplash

Wood also offers one of the simplest explanations for climate change, as well as the solution. The world’s carbon cycle is a constant movement of carbon throughout the planet between forests, rivers, oceans, land and animals. A tree or animal absorbs carbon to grow, and when it dies releases it back into the soil, air or water, through decomposition. For Millennia, this has been a balanced system, with similar levels of carbon constantly churning round the cycle. However, when humans discovered vast carbon rich reserves of ancient decomposed material — namely coal and oil — and started burning it, we began adding carbon into the atmosphere that belonged to a previous epoch’s carbon cycle. The carbon cycle became imbalanced, and CO2 in the atmosphere has been increasing far more rapidly than any time in the history of the Earth.

The solution to climate change is to stop burning those fossil fuels in the first place. But we have already burned more than we should, and we need to draw down the CO2 that has been released. Growing trees, felling them before they reach the decomposition stage, and keeping the carbon trapped within them as a building material — not just in small domestic houses but large commercial premises, too — is a crucial form of carbon capture and storage.

The carbon cycle over the last 800,000 years, and the relentless increase since the industrial burning of fossil fuels. Source: Nasa.

If we build with timber, as opposed to traditional materials with high levels of embodied carbon, we can save an average of 45 tons (40 tonnes) of CO2 per dwelling. At a global scale this can make a vital difference.

“Broadly speaking”, says Waugh, “using CLT allows us to construct lighter, better quality buildings, more quickly, with reduced foundations and fewer deliveries to site… We just built a 16,000 m2 building out of CLT — that would have needed around 1,000 cement truck deliveries for the frame alone. To deliver all the CLT, we needed just 92 deliveries. Less than 10% of the deliveries. Talk to people in Central London about the direct pollution of a thousand vehicles versus 92”.

As well as fewer deliveries, it is also safer for construction workers. Waugh takes me to a site that’s halfway through the build; a few relaxed construction workers walk around the fresh, pine-smelling site, with cordless screwdrivers. It’s far from the noisy, dangerous, power-tool dominated experience of most construction sites. He shows me a whole lift-shaft made from CLT. Builds that used to take years are now completed in weeks. The 4-storey Sky training building, built by Arup — another CLT pioneer — took just 11 weeks to construct the timber frame. According to Arup’s calculations, 1,057 tonnes of carbon dioxide equivalent is embodied — trapped — within it.

The sheer amount of wood on display when walking around CLT buildings has a perceptible calming effect, too. Human evolution, from our earliest ancestors onwards, grew alongside trees and wood as a building material. It brings us back to nature. Living and working within wooden buildings has been found to boost concentration levels, and even improve our sleep. A year-long Austrian study of high school students taught in either a wooden classroom or a linoleum and plasterboard classroom, found significant differences between the two groups: the students taught in the wooden classroom had decreased heart rates and stress levels, compared to their artificially furnished friends.

Orsman Road, CLT build site, during construction.

CLT is now taking off in the United States too. The large forests that once served the dying newspaper industry have fallen into disrepair across America, fuelling the wildfire crisis. According to Melissa Jenkins of the U.S. Forest Service, her department is now actively promoting mass timber. She told an Energy Study Institute briefing that many planted forests are now “too dense, especially with small-diameter trees, creating conditions that fuel intense wildfires… Mass timber creates an economic incentive to use forests sustainably while leaving them intact, making communities safer while also developing local economies.”

In 2019, 12 CLT facilities or processing facilities were operational or in development in eight states (AL, IL, ME, MT, OR, TN, UT, WA). Changes to the International Building Code (IBC) that deal with mass timber will allow the construction of mass timber buildings up to 20 storeys from 2021. California’s Forest Climate Action Team, created under Gov. Jerry Brown, also extols the benefits of long-term forest management and investing in and mass timber products that can store carbon long-term in the building sector.

Forest fire devastation. Photo by Marcus Kauffman on Unsplash

“The US is the market we’re watching carefully”, says Waugh. “The terrible forest fires are from timber industries that have disappeared — forests that were planted for paper 60 years ago. Now they are not managed… The biggest Opioid problems are in former timber communities that have been decimated by the death of forestry in the US… people that used to be employed by the forestry industry. At the same time as solving climate change, making better buildings, we can help rural economies… These vast forests are basically rotting and burning down.” It’s as if, he says, “we kept on breeding cows but we stopped eating beef”.

Earthquake zones are also interested in CLT. During earthquakes, CLT can flex and absorb energy from the vibrations, acting as a damper. “Milan Technical University and the Japanese Government took all our details from our first design, Murray Grove”, informs Waugh, “and they built a 7-storey building on a shake table in Japan, and shook it to Kobe [earthquake] levels” (see embedded video below). It “massively outperforms” concrete and steel, claims Waugh.

As humanity reassesses its relationship with the planet, so we need to transition from using extracted, polluting materials, toward natural, replenishable, carbon sequestering materials. Only by increasing tree cover can we start to reverse the damage done to the environment caused by burning fossil fuels.

By using timber as our primary construction material we can begin to remove the elevated amounts of carbon dioxide from the atmosphere. Ultimately, working with nature not against it, is where we must return.

Tim Smedley

Written by

Environment & tech writer for the BBC, Guardian and others. First book ‘Clearing The Air’ was nominated for the Royal Society science book of the year, 2019.

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