Materials such as steel and concrete have very high embodied carbon and both industries have published long-term plans to achieve net zero. They will continue to be part of our built environment, simply because of their ubiquity and usefulness. In the short term at least, low embodied carbon design means keeping their use to a minimum. What are the alternatives?
What bio-sourced materials are available?
In a building with a 60-year or more lifespan, the sequestered carbon of bio-sourced products has a measurable positive effect on whole life carbon.
For low-rise structures in particular, bio-sourced solutions are feasible and offer lower embodied carbon, especially for low-rise structures. Timber frame structures, and insulations such as wood fibre or hemp, are good examples.
Bio-sourced materials sequester carbon – that is, they draw carbon from the atmosphere as they grow – and they store that carbon for as long as they are used in the building.
The exact nature of how the carbon of timber products is accounted for in life cycle assessment can be subject to debate. And there simply isn’t enough global timber supply for wood to replace steel and concrete, while still providing the increased forest cover the planet needs.
The thoughtful and efficient use of bio-sourced materials, however, is a key part of the solution.
What is the embodied carbon of structures?
Establishing the embodied carbon of a product used in a building is fundamentally simple. Multiply the amount of the material being used by its embodied carbon per m3 and you have the total for that product. Do that for all the products in a building and you have the building’s total embodied carbon.
Add the predicted operational carbon for the building’s intended life and you have the building’s whole life carbon. This can then be used as benchmark against sustainability goals and targets.
Regardless of embodied carbon content, efficient use of materials is important. In addition to sustainability benefits, it also leads to cost savings. Designs should seek to use less-complex forms; in particular, reducing the amount of material that needs to go into foundations and structural frames is the ultimate aim.
Where that can be achieved at the same time as moving away from materials that have high upfront carbon, then a project will see substantial embodied carbon reductions.
Collaborating to make low carbon specifications a reality
Specifying different materials, like bio-sourced ones, means engaging with different manufacturers and supply chain partners.
It means obtaining different information, to better understand product performance and compare environmental impact. It also means understanding where products can be sourced from so that contractors don’t try to substitute more ‘usual’ products back into the specification.
The calculation of embodied carbon might be straightforward in theory, but requires information that you might not typically ask for. Understanding the volume of concrete in a design, say, requires engagement with the structural engineer. Not only to get accurate information, but first to communicate the goal of lowering whole life carbon through more efficient design.
Through this engagement and collaboration, the whole industry can begin to move away from an approach of ‘that’s how we’ve always done it’. We all need to work together to create a common culture that prioritises low carbon design and construction, and achieve that by sharing data and learning from one another.
About the author
Darren Evans - Business leader connecting with people to treat people and planet as the precious resources they are so that we can build a better future together https://darren-evans.co.uk/