Why our cities aren’t made of wood yet
Timber is seen by many as the solution to reducing carbon emissions from the construction sector. Helped by the introduction of engineered timber products, wood is able to compete not only with masonry, but also with concrete and steel.
Yet when you pass by any major construction site, chances are slim you’ll see much wood laying around. Most buildings, especially larger ones, are still made out of more carbon intensive materials.
The production of cement, a key ingredient in concrete, accounts for 8% of global CO² emissions, according to a 2018 report by Chatham House, a London-based policy think tank. Using wood as a construction material can significantly reduce those emissions.
Wood for Good, an industry campaigner for the use of timber in construction, says that a lack of understanding and knowledge within the industry on how to use timber, is one of the biggest barriers to growth.
There is also a historic hesitancy from the insurance sector related to safety concerns, said a spokesperson for the campaign. “This stems from reports published in the 1970s,” she added.
“In 2021 we have more data, research and innovation within the timber sector than ever before, which allows us to confidently use timber in a huge variety of applications safely.”
For the purpose of understanding the timber construction industry, it helps to distinguish between timber-framed structures, which are commonly used for individual houses, and engineered timber, which allows for taller buildings, such as residential tower blocks, or offices.
Cross-laminated timber
Engineered timber is a generic term for various products which combine multiple layers of wood to create solid panels or beams — sometimes also referred to as ‘mass timber’. The one that receives the most attention is cross-laminated timber (CLT).
To make CLT, kiln-dried boards, also known as lamellas, are stacked in perpendicular layers and glued together. Stacking the wood this way can create panels that match or exceed the strength of concrete and steel.
While CLT was devised only about 25 years ago, other engineered timber products have been around for much longer.
Dr Morwenna Spear, a researcher at the BioComposites Centre, said that glulam, another laminated timber product, was already in use decades ago:
“There were a lot of projects in the sixties, you know, things that you don’t realise have got timber in them. Like some of the structures in the Thames barrier — those iconic kind of arch shaped pieces are actually formed by glulam because of the way that you can make interesting shapes out of it.”
“We’ve got quite a lot of experience with engineered wood in this country, we just possibly don’t realise. We have moved on to other things, and now there’s a resurgence, so we’re just kind of bringing the skills back in,” she added.
Timber-framed buildings have also been around for a long time, and they are more common than CLT structures. The Structural Timber Association estimated that timber frame systems already represented over a quarter of all housing starts in 2016.
Dr Spear points out that individual houses, rather than flats, are the dominant form of residence in the UK — making timber frames an important part of the equation in lowering greenhouse gas emissions in the construction sector.
Carbon targets
To meet its targets for tackling the climate crisis, the UK needs to drastically reduce emissions from this sector. The government’s Climate Change Committee (CCC) proposes a 70% reduction by 2035 for manufacturing and construction combined. And in 2018, the construction sector made a deal with the government to achieve a 50% reduction in carbon emissions by 2025.
With the UN predicting that 68% of the world’s population will live in urban areas by 2050, it is likely that a large part of this reduction will have to come from high-density urban housing — the type of construction that can be done using CLT.
The carbon abatement potential for CLT is high, according to a report commissioned by the CCC. It found that replacing concrete with CLT could reduce a building’s carbon footprint by as much as 60%.
Besides being low carbon, construction using CLT offers certain advantages over building using concrete and steel. CLT panels are made to measure in a factory, ready to be assembled when they arrive on a building site. This means that construction is quicker and quieter compared to traditional methods.
Stimulating the use of timber
Around Europe, municipalities and national governments are starting to see the potential of engineered timber as a renewable construction material. The Amsterdam metropolitan area for instance, expressed the ambition last year that one in five new homes in the region should be made out of wood by 2025.
And in France, authorities have announced plans for a new sustainability law that will require new public buildings to be built using at least 50% timber or other biobased materials.
It is initiatives like these, says mass timber expert Pablo van der Lugt, that are important in stimulating construction using biobased materials.
“This is how developers and construction companies will see that it’s important to invest in these technologies, to invest in knowledge building, and perhaps even in their own factories. That’s how cost price will come down.”
Several comparison studies between CLT and concrete point to roughly equal prices when calculated for an entire building project. The Climate Change Committee backs this up in their report.
Despite that, Van der Lugt argues for a carbon tax on construction materials, which could further level the playing field:
“Traditional, non-renewable materials won’t score as well. They are manufactured cheaply, and the environmental damage that is caused by their production is currently ignored — that’s fundamentally unfair.”
The UK is in a unique position to lead Europe in the transition to a sustainable construction industry. Van der Lugt says that while Scandinavia, and countries like Germany, Austria and Switzerland traditionally have built more using timber, Britain is actually ahead when it comes to construction using mass timber products, such as CLT.
Cross-laminated timber represents only a small percentage of the total market at present, but Dr Spear says it has seen exponential growth over the past few years. “It takes several years of exponential growth before you start to make a dent in the total figures,” she adds.
Asked what is needed to further stimulate the growth of timber, she pointed to guidance put out by professional bodies on calculating embodied carbon emissions for construction projects.
The Royal Institution of Chartered Surveyors (RICS), for example, has created a database to identify and track carbon emissions in all stages of a building’s lifecycle.
“There is a move within the construction sector as a whole to start looking at the embodied carbon of their buildings and it’s being led by concern about greenhouse gas emissions”
She also says the government has a responsibility to do more:
“They are aware of the need to do something with it [timber]. You can see that in the various sector deals that are being made. But I think we need to see that actually trickle down to support — whether that’s through local education to train people in the industry, or support for businesses to help swap one technology for the other.”
For a start, England could learn from the rest of Britain. Experts say that Wales and Scotland currently lead the way in promoting timber. According to Wood for Good, around 85% of new homes in Scotland are already constructed using wood.
“In England, we need a combination of policy incentives, removal of legislative barriers, increased awareness within the sector and education on how to specify timber to see more timber buildings being constructed,” they say.
Dr Spear adds that “Welsh and Scottish governments have been very good in supporting the supply chain and the business end, to promote timber frame building. For good practice, I would point people there.”
Originally published at https://www.thatfigures.org on July 2, 2021.
