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Architects are increasingly using mass timber in the hopes of creating net-zero buildings but carbon assessments are missing key sources of potential emissions, researchers tell Dezeen in this Timber Revolution feature.

The standard method for determining a building’s overall carbon footprint is a whole-building life-cycle assessment (LCA) that breaks down emissions at every stage – from the sourcing of raw materials to their ultimate disposal.

These calculations tend to indicate significantly lower emissions for timber structures compared to those made entirely out of concrete and steel. But experts warned that LCAs only tell part of the story.

“LCAs do not typically consider anything that happens in the forest,” said forester and timberland manager Mark Wishnie.

“And the land management side is, from a climate perspective and a biodiversity perspective, enormously important,” added Steph Carlisle of the Carbon Leadership Forum research group. “That’s really where all the action is.”

End-of-life “very, very important”

Because so few mass-timber buildings have been constructed – let alone demolished – researchers are also unable to reliably forecast what will happen to engineered timbers at end of their life and what emissions this would entail.

“There’s not a lot of data available to predict end-of-life and that can be very, very important,” Wishnie said.

This leaves both researchers and architects with an incomplete picture of mass timber’s climate impacts, which urgently needs to be addressed if the industry is to scale up sustainably without adverse effects on the environment.

“We need better transparency and traceability,” Carlisle said. “When architects use tools and they don’t necessarily know what’s going on behind them, they can really mislead themselves about the real emissions.”

“If we get this right, it has such incredible potential,” added Robyn van den Heuvel of the Climate Smart Forest Economy Program. “Not just for the built environment but also to ensure forests are sustainably managed.”

“But there are incredible risks of getting this wrong. It could result in the exact opposite effects of what we’re trying to create.”

Badly harvested timber has higher embodied emissions

Timber’s climate potential lies in its ability to sequester large amounts of CO2 from the atmosphere during its growth – in contrast to common building materials like concrete and steel, which mostly just produce emissions.

As a result, mass timber has been widely hailed as a way to help architects make their buildings net zero and, by extension, help the built environment mitigate the 13 per cent of global emissions that stem from the construction of buildings and the materials used in the process.

Research indicates that substituting wood for steel and concrete in mid-rise buildings could reduce emissions from manufacturing, transport and construction by between 13 and 26.5 per cent, depending on the building’s design, the exact wood products used and where they are shipped from.

But due to a lack of data, the International Institute of Sustainable Development (IISD) has warned that LCAs can gloss over the huge impacts that forest management and end-of-life can have on the overall climate impact of a mass-timber product.

Forest management is an important part of the equation, not just because it can help to prevent deforestation and protect biodiversity but also because it has a huge impact on a forest’s ability to act as a carbon sink.

Felling all the trees in a forest at the same time, in a method known as clear-cutting, can generate significant emissions by disturbing the soil and releasing the carbon it stores, which accounts for almost 75 per cent of a forest’s total carbon stock.

When this is combined with other harmful practices such as converting old-growth forests into tree plantations, this could actually make a timber building more emissions-intensive than a concrete equivalent, the IISD suggests.

“It’s neither true that all wood is good, nor that all wood is bad,” said Carlisle. “Architects really need to understand that it matters where your wood comes from.”

Forest certifications falling short

However, none of these important land-management impacts – whether good or bad – are reflected in typical life-cycle assessments.

“They don’t account for an increase in forest carbon stock or a decrease in forest carbon stock, an increase in forest area or a decrease in the forest area,” said Wishnie.

“Often, if you’ve got that wrong, it doesn’t matter what else is happening in the value chain, you already have a bad carbon story,” agreed van den Heuvel, who leads the non-profit Climate Smart Forest Economy Program.

To some extent, these concerns are addressed by forest certification schemes – the most comprehensive being FSC, which covers crucial factors such as forest health, biodiversity, water quality, and Indigenous and workers’ rights.

But these certifications do not require forestry companies to track and quantify how different management practices impact the carbon stock of a forest, which makes them impossible to represent in the LCAs used by architects and building professionals.

6 Orsman Road by Waugh Thistleton Architects in London — 6 Orsman Road is a demountable timber building by Waugh Thistleton. Photo by Ed Reeve

“Right now, I have no way of representing FSC-wood accurately in a life-cycle assessment model,” said Carlisle, who is a senior researcher at the Carbon Leadership Forum.

“There’s a lot of work happening on the certification side to do that research and publish it so it can come into our models. And we really need it because it’s not going to be sufficient in the long run for certification to be a stand-in.”

FSC certification is applied to 50,000 companies globally, making it harder for architects to discern which of these companies provides the best forest management and the most sustainable, lowest-carbon product so they can vote with their wallets.

“As the user, I can’t really make choices,” said Simone Farresin, one-half of design duo Formafantasma. “I can’t evaluate if one seller is better in community support or another in sustainable growing. It’s certified and that’s it. It’s not specific.”

“When you’re looking at materials, you have all these different grades of quality,” he continued. “And we need to reach the same in terms of sustainability – we need to be able to detect these different grades.”

“No consensus” over end-of-life emissions

Another area that is lacking in reliable information, and therefore hard to represent in LCAs, is what happens when a mass-timber building is demolished.

“There is a lot of debate about how to model end-of-life and it gets really contentious really quickly,” said Carlisle. “There is no consensus. The fight is very live.”

If a building was designed for deconstruction and its timber components are reused, this could offer substantial carbon and ecosystem benefits – providing continued long-term carbon storage while reducing the need for renewed logging as well as for emissions-intensive steel and concrete.

A small number of architects have begun to deliver demountable mass-timber buildings to facilitate material reuse, such as Waugh Thistleton’s 6 Orsman Road in London.

However, most timber demolition waste today ends up in either landfills or incinerators, with both scenarios resulting in some net emissions.

“Depending on what country you’re in, that waste looks very different,” said van den Heuvel. “But that also has a really massive impact on your total carbon story.”

In the case of incineration, all of the carbon stored in the wood would be released into the air, negating any storage benefits but potentially generating renewable electricity in the process if burned for biomass energy.

In a high-quality modern landfill, on the other hand, engineered wood products are estimated to lose only around 1.3 per cent of their carbon, although part of this carbon is released as methane – a powerful greenhouse gas that is 80 times more potent than carbon dioxide over a 20-year period.

“This is counterintuitive to people,” Carlisle said. “But you see very small emissions at end-of-life from landfills because that material is largely considered sequestered and stored permanently.”

“We can’t aim for perfection”

Crucially, estimates about end-of-life emissions are mostly based on products like medium-density fibreboard (MDF), which are less elaborately engineered than structural materials such as cross- and glue-laminated timber and so may respond differently.

“There is more uncertainty around what will actually happen at end-of-life because there are so few mass-timber buildings,” Carlisle said.

Researchers and institutions such as the Carbon Leadership Forum and the Climate Smart Forest Economy Program are working hard to fill in these gaps. And ultimately, they argue that governments must set national and international standards to ensure responsible sourcing and disposal if we hope to accurately assess and realise mass timber’s climate potential.

But in the meantime, all parts of the timber value chain – from forest managers to manufacturers and architects – should be more transparent about their carbon accounting.

“I would hate to see a world in which we stop everything to make sure all the certification is perfect,” said van den Heuvel. “Because buildings are still going to get built. And if we’re not using mass timber, we’re using a product that’s going to be even worse for the environment.”

“We’re running out of time, so we can’t aim for perfection. We should aim for good enough and transparency around it so that others can improve.”

The top photo is by Maksim Safaniuk via Shutterstock.

Illustration by Yo Hosoyamada

Timber Revolution
This article is part of Dezeen’s Timber Revolution series, which explores the potential of mass timber and asks whether going back to wood as our primary construction material can lead the world to a more sustainable future.

Reference

Wooden interior of John W Olver Design Building at the University of Massachusetts

Sustainable News

Mass timber buildings can have high carbon emissions says Amy Leedham

By Zarkon Group,30/03/2023

Mass timber’s reputation as the go-to low-carbon construction material is a problematic oversimplification that is leading to greenwashing, says carbon expert Amy Leedham in this Timber Revolution interview.

“We’re seeing a little bit of oversimplification and glorification of mass timber,” said Leedham, who is carbon lead at engineering consultancy Atelier Ten.

“The main thing that you see in the media, and one of the reasons it’s becoming such a popular building material, is that it can have a significantly lower embodied carbon than steel or concrete,” she told Dezeen. “I say ‘can’ because it’s not always the case.”

Mass timber is a term for engineered-wood products – strong structural components that typically consist of layers of wood bonded together.

It is increasing in popularity in the construction industry due to wood’s ability to sequester carbon, which means timber generally has a lower embodied carbon when compared to materials such as concrete and steel.

However, according to Leedham, this has caused mass timber to become synonymous with carbon neutrality, leading to the fallacy that all “mass-timber buildings are carbon neutral” due to the stored carbon offsetting the emissions expended by them.

“Critical factors that need to be considered”

“Mass timber construction can definitely be an important pathway toward carbon neutrality, but there are other critical factors that need to be considered,” she told Dezeen.

“If it’s not done well, mass timber buildings can have very high carbon emissions, whereas concrete buildings can have quite low carbon emissions,” she said.

“We’ve worked on concrete projects with certain concrete suppliers where they’re really focusing on reducing emissions associated with the concrete mixes and those can have quite low carbon emissions. There’s no black and white, it’s all hues of grey.”

Render of the Portland Museum of Art extension — Atelier Ten has designed the mass-timber extension of the Portland Museum of Art with Lever Architecture. Image by Darcstudio

Carbon neutrality is achieved when no additional carbon dioxide is added to the atmosphere in the creation and operation of an entity, such as a building. This can either involve eliminating emissions in the first place, negating emissions through offsetting, or a combination of both.

Assuming that using mass timber achieves this through its sequestered carbon alone can overlook several factors, such as the carbon footprint of other materials used to construct wooden buildings, including the interior finishes.

“Mass timber buildings have a lot of other material in them, especially in places where the code is challenging, especially for taller mass timber,” Leedham said.

Additionally, the carbon footprint of mass timber can also be impacted by how and from where the wood was sourced and transported, and what happens to it at the end of its useful life.

If the wood used in a building’s construction ends up in a landfill, it is likely to be incinerated or left to decompose, with its sequestered carbon released back into the atmosphere – cancelling out the carbon benefits.

“We can only control up to the point that the building is built”

“Forestry practices are super important to the overall carbon impact of mass timber, as well as end-of-life treatment,” explained Leedham.

“As designers and engineers, we can only control up to the point that the building is built. We can design in certain aspects so that it can be treated well at the end of its life in 100 years, but we don’t know what’s going to happen.”

The overlooking of these “critical factors” recently prompted Leedham to write a series of myth-busting essays on engineered wood, co-authored and published with US studio Lever Architecture.

The essays shine a light on the main misconceptions about mass timber that are circulating in the industry, in an effort to expose the truth behind them and promote the responsible use of the material in architecture.

“Mass timber is super important to the future of low-carbon construction,” she said.

“But it’s also really important that it’s done right. If it’s done incorrectly, then it’s just another form of greenwashing.”

Alongside the misunderstandings about mass timber and carbon neutrality, the essays also debunk beliefs that “all wood is good wood”, that it is always more sustainable than concrete, and that mass-timber buildings actually absorb carbon.

Co-author Jonathan Heppme, who is a principal at Lever Architecture, said the authors have heard these myths in discussions about their own projects, but also at industry events.

“These myths emerge very frequently”

“Variations on these myths emerge very frequently where architectural and engineering professionals meet to discuss construction and procurement with project owners, builders, manufacturers and trade representatives,” Heppme told Dezeen.

“These myths surface at symposiums, trade shows, conferences, lectures, or in conference rooms where decisions around the incorporation and advancement of mass-timber systems are being discussed,” he continued.

Both he and Leedham hope their publication will contribute to “more nuanced narratives from the mass timber industry” and advocate “healthy innovation” in this space.

In the essays, the authors outline how the industry can combat these myths – such as by encouraging architects to make conscientious sourcing decisions, which can, in turn, incentivise the timber industry to manage forests sustainably, and by improving understanding of carbon neutrality and how it can be achieved.

Timber-steel structure inside John W Olver Design Building in Massachusetts — Leedham believes timber, steel and concrete all have roles in the future of architecture. Photo is of John W Olver Design Building in Massachusetts by Albert Vecerka/Esto

Leedham told Dezeen that these solutions could also all be supported by the roll-out of worldwide carbon taxes for construction projects, which would require payments for the greenhouse gas emissions emitted by building components.

Not only would this lead to the more responsible use of mass timber, she said, but it would also encourage more sustainable practices when it comes to using materials such as concrete and steel.

“Carbon taxes would definitely speed up the adoption of any type of more sustainable construction practice,” said Leedham.

“If you had to pay for all the carbon emissions before you got your building permit, I think that would encourage the use of mass timber, it would encourage sustainable forestry practices, and it would actually encourage both the concrete and steel industry to reduce their emissions.”

Mass timber will not “dominate the industry”

This last point is particularly important as she believes that concrete and steel will remain vital materials in the future of architecture.

“The reality is that we need everything. Mass timber is one of a kit of parts,” said Leedham.

“I don’t think mass timber is going to ever dominate the industry, just because of the sheer volume of construction that’s happening, and I don’t think it wants to.”

“We absolutely need steel and concrete industries to also focus on reducing their emissions because we’re going to need all three primary structural materials,” she added.

This echoes the views of construction material expert Benjamin Kromoser, who told Dezeen in an interview that mass timber will not become a mainstream building material because it uses too much wood

“Wood is a limited resource,” he said. “It always has to be a balance between what we take from the forest to use for building construction and how much grows again.”

Illustration by Yo Hosoyamada

Reference

Interior of Ibstock Place School Refectory in Roehampton by Maccreanor Lavington

Sustainable News

Mass timber “definitely not the right way to go” says Benjamin Kromoser

By Zarkon Group,24/03/2023

Mass timber will not become a mainstream building product because it uses too much wood, construction material expert Benjamin Kromoser claims in this interview for the Timber Revolution.

“If we go more in the direction of mass-timber buildings we don’t have enough material, so the idea of scaling it up in the near future will fail,” he told Dezeen.

“I think there will be a possibility to scale it up a bit, so its use will go up in the next few years – especially in Sweden and Norway, where they have built quite a lot of cross-laminated timber production facilities.”

“But from my point of view, I think we will reach the maximum of mass timber in at least 10 years. I think, really, it will be before 2030.”

“Using wood doesn’t [automatically] make a building sustainable”

Kromoser leads the Institute of Green Civil Engineering at the University of Natural Resources and Life Sciences (BOKU) in Vienna, which receives funding from both industry and public sector organisations.

He believes that the main challenge for the building industry is using fewer raw materials overall, rather than simply switching from concrete and steel to biomaterials like wood.

“Our aim is to minimise the environmental impact of buildings over the whole lifecycle,” he said.

“Using wood doesn’t [automatically] make a building sustainable, because basically, what we have as a problem is that in total we need too much materials.”

Mass timber is the term given to engineered wood products like cross-laminated timber (CLT) and glued laminated timber (glulam), which typically constitute layers of wood bound together to form strong structural components.

“Wood is a limited resource”

Because trees sequester carbon from the atmosphere, replacing heavily polluting man-made materials like concrete and steel for timber can significantly reduce the embodied carbon footprint of buildings.

But while mass timber can be used for taller buildings than conventional timber-frame construction, it uses much more wood. That leads Kromoser to doubt its overall sustainability.

“Wood is a limited resource,” he said. “It always has to be a balance between what we take from the forest to use for building construction and how much grows again.”

“If we go in the direction of building everything with CLT, then maybe from the point of view of temporarily storing CO2 it would be great, but it’s definitely not really possible to scale that up.”

Catalyst building by Katerra — Mass timber usually consists of layers of wood bound together to form strong structural components. Photo courtesy of Katerra

Even in Austria, where around half the country is forested, he is doubtful it would be possible to translate that into half of new buildings in Vienna being made from mass timber.

Instead, he argues that to increase the proportion of construction that uses wood, more material-efficient methods like timber frame must take precedence.

“It would be great if we could build 50 per cent of the buildings in Vienna out of wood but we are far away from that regarding the availability of the materials, so going in the direction of mass-timber construction is wrong,” he said.

“We have to go in the direction of using timber in the most efficient way and that means structurally optimised buildings, so mass timber is definitely not the right way to go.”

“Timber framing is much more efficient, and you can quantify that with a life-cycle assessment.”

Need to “decouple” material use from economic growth

To produce one metre-cubed of CLT or glulam, around 2.5 metres cubed of wood is required, roughly 25 per cent more than for timber-frame construction.

Kromoser argued that mass timber’s main application should be for creating cantilevers or bearing heavy loads, or for living spaces in attic rooms thanks to its thermal massing properties.

“Timber is a great material, and mass timber where it has its justification is a good thing,” he said. “But thinking about how the building can be structurally optimised is a really important thing to keep in mind.”

“That’s my key message, because then we can reduce the amount of raw material required and then we can build more out of timber,” he continued.

He argues that depicting mass timber as a golden ticket to decarbonising the built environment could risk distracting from the main issue of material use.

“If you’re speaking about a big potential in mass timber construction, it could justify for our society, ‘if we use this material, it doesn’t matter anymore how much we use’. That’s absolutely not right.”

The major challenge, according to Kromoser, is to decrease the use of raw materials while still enabling the growth of economies around the world.

“Further development of society is always linked to an increase in materials, and that’s the wrong direction,” he said.

“So what we really have to think about is how we decouple the connection between material use and the further development of society. That’s the biggest issue and it’s not linked to construction material.”

The top photo is courtesy of Benjamin Kromoser.

Illustration by Yo Hosoyamada

Timber Revolution

This article is part of Dezeen’s Timber Revolution series, which explores the potential of mass timber and asks whether going back to wood as our primary construction material can lead the world to a more sustainable future.

Reference

Mass

The hidden environmental impacts of getting mass timber wrong

Mass timber buildings can have high carbon emissions says Amy Leedham

Mass timber “definitely not the right way to go” says Benjamin Kromoser

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