COMMENT Half of a building’s total lifetime carbon is emitted during construction, according to the World Green Building Council, making building reuse essential to cutting carbon emissions.
However, this is just the first step. The choice of the materials used in the reinvention and restoration is a key part of the equation. According to the Global Alliance for Buildings and Construction, just three materials – concrete, steel and aluminium – are responsible for 23% of carbon emissions worldwide, illustrating just how much materials do matter.
While much of the construction industry continues to rely on energy-intensive material production and extraction, turning to low-carbon and regenerative materials, such as cross-laminated timber, or CLT, is a clear way to bring emissions down. CLT can be brought in as an alternative to concrete and steel, which, thanks to its lightweight and versatile structure, can unlock and bring new life to difficult building assets.
Although timber is gaining momentum in new-builds, its use in retrofit remains limited. Understanding the opportunities and challenges that this material can provide, and finding new applications, could be a game-changer when it comes to protecting our finite resources.
Going with the grain
CLT is primed to become one of the most crucial materials for mass construction as we strive to meet net-zero targets. However, the UK is something of an outlier in the CLT market. We remain a long way behind the Netherlands and Scandinavia, where timber-built towers, such as Studio Marco Vermeulen’s Dutch Mountains in Eindhoven and White Arkitekter’s Sara Cultural Centre in Skellefteå, Sweden, are pioneering the scale of timber construction.
Closer to home, architecture practices such as Waugh Thistleton are paving the way for the use of CLT in the UK’s city centres, with some great examples showcasing how timber can improve the speed and efficiency of construction on constrained urban sites.
This versatility makes CLT an ideal material for reuse and is why we have been looking for ways to maximise its use in our projects. Technique, completed last year, used glulam for the three-storey extension of a former gin distillery in the heart of Clerkenwell. This choice allowed us to make embodied carbon emissions savings of 43%, while transforming a former industrial space into a light-filled, state-of-the-art workplace.
We are also using CLT to extend the former Woolworths HQ on Marylebone Road, now called Metropolis. The material has allowed us to navigate the challenges of adding additional storeys to the original building and increasing floor-to-ceiling height, while doubling the usable floor area.
Although CLT has clear advantages over energy-intensive materials, when it comes to reuse, there are still several barriers stopping the UK from going with the grain.
What is holding us back?
In a post-Grenfell context, industry bodies are rightly wary of the safety of construction materials. Recent policy changes, such as the UK government’s 2018 ban on combustible materials for cladding, have slowed the adoption of timber over less sustainable options like concrete and steel. This has given CLT an image problem, despite ongoing R&D demonstrating its ability to meet and exceed safety standards.
As a result, most insurers require the use of light timber hybrid to pass requirements. In terms of building reuse, owing to the reduced perceived risk, timber tends to be relegated to extensions (given the floor area typically represents less than 50% of the building), thereby bringing down the ratio of timber vs traditional materials. However, these measures fail to recognise the strides being made in improving the structural and fire safety performance of timber, and ultimately make it harder to realise the benefits of using regenerative materials at scale. Aviva’s decision to increase backing for timber developers is a promising sign, but more needs to be done to improve financial support for CLT builds.
Additionally, as it stands, the UK lacks the home-grown materials and skills needed to scale up timber construction. According to the House of Commons Environmental Audit Committee, the UK imported 81% of its timber in 2021, making it the second-highest net importer of wood worldwide. This is despite our green and pleasant land having more than 3.2m hectares of tree cover. With the costs of materials rising, we are clearly missing a trick by failing to invest in local skills and manufacturing. Timber Development UK’s Timber Skills Action Plan is a welcome initiative for the future of green jobs across the country, and should go hand-in-hand with investment in timber production.
CLT presents a key solution in the race to future-proof the built environment. However, the way ahead requires a change of mindset before regulations can follow. The UK needs to move on from its love of steel and concrete and get back to regenerative alternatives, not only for new-builds but also for unlocking building reuse. The marriage of restoration and CLT is just what we need to bring about a more sustainable future for construction in the UK.
Jacob Loftus is chief executive of General Projects
