Given that construction is responsible for well over half of the extraction of virgin resources, and contributes to some 60% of total waste streams, we as engineers have a responsibility to ensure we use materials wisely.
Applying circular economy principles to structural design is one key practical part of moving towards Net Zero
; we need to maximise the value of material and minimise embodied energy to deliver.
In engineering, this means:
- Creatively seeking opportunities for reuse
- Optimising for whole life scenarios
- Designing for deconstruction
These targets become part of our brief for good design. With practice, it will become as natural as historically selecting the best material for the job.
Reuse (or partial reuse)
First in the hierarchy of the circular economy for the structural engineer comes reuse. You’ve probably taken this approach many times before, some of this is not new. Some of it might be.
For structural engineers, on the site of an existing development, the building structure and foundations will be the primary asset.
Can it be adapted to suit a new scheme? Can a cut and carve approach unlock new ways in which the building can work (and will this actually save the client programme time and money)? Can the foundations take an increase in load to suit additional storeys?
Think of these as a design review of the existing structure rather than a set of rules.
Maximising circular approach also involves interrogating the existing building to advise the client on how the shorter life components could be disassembled from the main structure for reuse. For example, can it be determined whether components are connected to the structure with reversible mechanical fixings when intrusive surveys are being carried out?
By including these sorts of investigations, it reduces the risk for the client when the contactor prices for disassembly.
New-build and whole-life thinking
Circular guidance advises us to design buildings for the future addressing longevity, flexibility, adaptability and assembly, disassembly and recoverability.
Therefore, for structure and its life range of say 30-300 years, lean design with a long life and loose fit will be the best contribution to the circular economy, whole life carbon and likely whole life cost.
So, how do you do that? And how does it fit in with the ‘shorter life’ of other building components (which are designed in the circular world for easy maintenance, disassembly and remanufacture)?
Practically, this means avoiding the interdependency of the structural frame and other components (such as the façade), so that they can be easily separated, and the shorter life components can be renewed in a straightforward way.
We must also consider material choices. For example, in a scenario where a potential lack of maintenance will lead to degradation, the upfront increases in cost and carbon related with stainless steel may be worth the investment if the painted mild steel alternative is likely to need replacing sooner.
Of course, a whole life approach requires the industry to consider how the value of investment is captured; there must be evidence that a quality building is able to get better rents and higher sales values. And for the ‘new’ development, can materials be reused from another project? Probably.
As the Built Environment moves more firmly this way, material inventories and databases will make this easier. In the UK, WRAP have a helpful guide
which includes a directory of reclaimed materials - other countries may have similar resources.
You’ll probably need to also devise a contingency plan, in case those materials are no longer available – perhaps sharing knowledge of assets between firms could be part of the solution?
Facilitating reuse and low carbon
To facilitate reuse for others in the future, ensure that the BIM
is adequate to record this. Ensure the handover information at the end of the project always includes a deconstruction and reuse methodology, regardless of what other circular aspects have been incorporated (or not) so far.
Finally, if some elements of the building are truly virgin, they should be lean within the long life and loose fit approach. Ensuring low-carbon though the supply chain will necessitate modifying specifications to suit (for example specifying Electric Arc Furnace steel over Basic Oxygen Furnace steel, halving the embodied carbon of the material).
Taking just a few key approaches can make a big difference. The circular economy is so important because it is really fundamentally about whole life, which is at the top of the hierarchy for sustainability
, whichever way you want to look at it.