• Isabel Clifford

A wooden future – is timber the new concrete?

Credit: PLP Architecture

Sustainability researcher Isabel Clifford says timber should replace concrete as the world’s dominant building material, drastically cutting global CO2 emissions.

Urban populations are growing and so carbon emissions from the construction industry are becoming increasingly important in the battle against climate change.

These days, modern construction mainly involves (reinforced) concrete, a material which is experiencing significant growth in consumption worldwide, accounting for a whopping 8.6% of all global CO₂ emissions.

Additionally, a substantial amount of sand is needed to produce concrete; a resource fundamental for carbon storage in marine ecosystems and one that is under pressure from global over-extraction.

By contrast, timber could return to centre stage: it is a natural material with low emissions in its manufacturing process, and sequestered CO₂ within the material allows buildings to actually store large amounts of carbon!

Timber already makes up the frames of most new build family homes in the UK, and has become a focal point for modern architects who envision broadening its application to create a wooden future. Some are even designing plans for skyscrapers. PLP Architecture have proposed a 300m multi-use timber high-rise building to be erected in the Barbican, London.

But wood needs to evolve if it is to become strong and reliable enough to be used in as many elements of construction as possible.

Engineered wood such as cross-laminated timber (CLT) is one way this evolution is happening. CLT – which is formed by bonding multiple layers of wood together at right angles - has an impressive weight-to-strength ratio making it suitable for load bearing walls and floors, and offsite fabrication allows buildings to be assembled rapidly.

Uptake of CLT in the construction industry provides an opportunity to maximise the versatility of wood, and therefore to decarbonise the built environment, potentially turning cities into vast carbon sinks which store CO₂ alongside forested areas.

What's not to like?

Despite its enormous potential, timber is not without its problems.

Firstly, forestry and timber harvesting. Left unmanaged, timber harvesting has the potential to destroy forests and ecosystems, which would, of course, only exacerbate the climate crisis. If timber is to become a major building material, strict forest management and global certification schemes (such as through the Forestry Stewardship Council) need to be a priority. In addition, regular assessments could be undertaken to measure and track carbon throughout all lifecycle stages of the timber. To further cut emissions, locally grown timber can be prioritised.

Arguably, fire safety is timber’s next biggest hurdle, and there are some regulatory challenges in the way of CLT being adopted across the board in the UK. Namely, the national fire safety regulations.

The Building Regulations of 2010 “require that external walls of buildings adequately resist the spread of fire over the walls and from one building to another”.

Alone, this regulation would not pose any difficulties for CLT, and it is right that fire safety is taken in to account.

However, UK regulations in this area have become much stricter in light of the 2017 Grenfell Tower fire (caused by flammable cladding used in the tower’s refurbishment a few years earlier) and the government has introduced a ban on the use of combustible materials on the external walls of high-rise residential buildings.

This ban poses a major obstacle for CLT. Not only directly with regards the residential high-rise buildings that it applies to, but on the possible public perception of CLT in other applications, possibly making the UK’s emission reduction targets even harder to achieve.

Unlike untreated timber, CLT in fact has an excellent fire resistance rating. With as few as 3 layers, CLT can be highly fire resistant, and increased numbers of layers and layer thickness can improve this further. CLT has been proven to pass fire safety tests and chars below the minimum rate required for building regulations.

In fact, CLT has been shown to perform better in fire tests than some steel and concrete components.

A cross section of an 88mm CLT element after fire tests. As can be seen, the charred area is only a few mm thick and the majority of the wood is undamaged. Credit: trada.co.uk

There have been mixed reactions to this ban. Many architects argue that it is unnecessary and will have detrimental impacts on timber construction and climate change, and there are calls on the government to revisit the ban and focus it on combustible cladding rather than the materials of the external walls themselves.

Alternatively, some architects say the ban is incentive for innovation and only applies to residential buildings over 18m tall. This leaves room for CLT to be used in other types of buildings such as offices. It can also be used with other materials such as a “structural CLT core and floors” while other materials such as steel can be used on the external walls.

So, even without revisions to these regulations, there is still room for timber to be incorporated into new builds, and we can hope that once this happens, public trust will only increase as misconceptions of engineered timber are cleared.

Even today, it seems that many of timber’s issues can be overcome. Given the urgency to reduce carbon emissions, doesn't this mean we should be aiming for a wooden future, with cities scattered with timber office blocks and one day maybe even skyscrapers?