POSSIBILITIES
TWO EXPERTS: ONE BELIEVER – ONE SCEPTIC
X files:
Do we need to accelerate the transition to timber buildings?
The believer.
WILL BELFIELD
The climate emergency we’re facing has brought to light the importance of a faster adoption of engineered timber in construction. Mass timber has major sustainability, aesthetic, wellbeing, and programme advantages – and, amazingly, offers a similar structural strength to concrete despite having a much lighter mass.
As the grid decarbonises, the proportion of emissions from building operations will diminish and embodied emissions will take precedent. The best place to start in reducing this embodied carbon is within the structure of a building as it represents roughly 50 percent of the total emissions.
If cement (the primary constituent of concrete) was a country, it would be the third largest carbon dioxide emitter in the world. By comparison, timber is classified as a renewable material, and the carbon emissions released during the processing and production are low.
Timber is lighter than typical construction materials, which is great for existing buildings as a timber roof extension is the most carbon-effective solution to deliver new floor space.
Yet perhaps the most significant benefit of timber is its ability to store carbon. Taking this sequestered carbon into consideration, timber buildings become key to delivering net-zero-carbon buildings: in a fully timber structure the reduction in upfront carbon compared to a conventional building could be as much as 60 percent.
CIrcular design
Timber has major circular economy benefits and CLT in particular lends itself to modular construction and designing for disassembly. Added to this, the more we promote the use of timber and drive demand, certifications such as FSC and PEFC mean further forest growth will occur to maintain the supply – subsequently creating more carbon capture.
We have a vital responsibility in our industry to meet the net-zero-carbon goals of 2030 and 2050 respectively. Is mass timber’s current use as widespread as it should be, given all its advantages? The answer is a resounding no. Ultimately, timber is a key route to the climate-conscious buildings of the future… the transition can’t come quick enough.
The sceptic.
LOUIS CHAUMONT
Mass timber clearly has a huge role to play in delivering the net-zero-carbon built environment we need. However, there are a number of key challenges in delivering mass timber buildings – both at scale and cost effectively – that the industry is currently working hard to overcome. It’s clear we should be transitioning to them as soon as we safely can, by increasing confidence and knowledge within the industry.
A key factor to be aware of is that there could be issues with the supply chain if the use of timber were to expand too rapidly. Therefore, it should be noted that timber cannot get us to a net-zero future alone; it must be accompanied by the transition of other core structural materials, for example, net-zero-carbon steel.
Yet the main area of importance is to fully understand fire behaviour in such buildings. Engineered timber has so far been used mainly for low-rise residential, commercial, and mixed-use buildings. Now, as new technologies and awareness improves, architects and developers are beginning to propose high-rise buildings constructed with CLT. However, this creates a level of complexity when it comes to fire safety, due to the additional fire loading compared to traditional buildings. Added to this is the fact that, due to the engineered timber’s composition and behaviour in fire, the standalone assumption of using the charring rates doesn’t allow us to achieve an adequate level of safety.
As such, alternative fire engineered solutions need to be explored to ensure that mass timber buildings can withstand a compartment burnout. The impact of mass timber elements on other aspects of a fire safety strategy also need to be assessed, including: internal fire spread, vertical fire spread over the façade, or external fire spread to neighbouring buildings.
There is currently no guidance available in the UK to base the design of large mass timber buildings on and meet these objectives. Thankfully, through performance-based design and fire testing, we can ensure that the functional requirements of Building Regulations can be met. So while these materials present an additional level of complexity when it comes to fire safety, it’s a challenge we can easily overcome with the right level of understanding and expertise. Ultimately, this transition is needed as soon as possible to create innovative sustainable buildings that are safe for their occupants.
Photo by bantersnaps, Unsplash