First Cuts Are The Deepest

When it comes to carbon, the earlier you start, the bigger impact you can make. At our events and CPD presentations, designers often ask about new products, and what to specify for the lowest-carbon concrete. It’s an important question and there’s always lots we can say: lower-carbon options are constantly expanding as innovations reach the mainstream and manufacturers decarbonise.

But if that’s the first time they’ve considered embodied carbon, it’s a major missed opportunity. As a design develops, opportunities become progressively more limited, moving along a continuum from “strategies” to “tweaks”. By the time it reaches technical design, significant, unnecessary carbon may have already been embedded. This is a common complaint from suppliers, frustrated that high-carbon solutions have already been baked in by the time they are set the challenge of reaching carbon targets.

The first thing to consider, at concept stage, is material efficiency: could you achieve the same result with less? Experienced designers will have a rough idea of the cost implications of early decisions. There is a growing understanding of how aspects like form factor (the ratio between internal floor area and external surface area) affect energy consumption. What we haven’t yet fully developed is an equivalent sense of the carbon impacts, or established rules of thumb for low embodied carbon design.

For concrete frames, our free spreadsheet-based CONCEPT tool can help, by illustrating how even small changes can impact carbon, cost and construction time. For precast, our forthcoming guidance document on low-carbon solutions will highlight the importance of aligning designs with manufacturing processes. Some of this is intuitive, and carbon can be analogous to cost, as with maximising repetition and standardisation. But a lot may not be – such as the impacts of window reveal depths and joint locations in precast cladding, or the greater efficiencies that can be derived by integrating services or facing materials.

The other way designers inadvertently embed carbon is by being overly prescriptive, and setting misguided or arbitrary criteria. Our Application article explains how recycled concrete can be used as aggregate in new concrete – but also how this is often not the lowest carbon option, or the best use of demolition waste. It’s always nuanced, because concrete is not a single product but a mix of many possible components, each bringing different properties and carbon values.

That’s why the best results happen when designers and makers work closely together. Our Origin Story profiles the stunning tree-trunk columns that grew from collaboration between Squire & Partners and Thorp Precast at Tide Bankside, which also boasts (less visibly) Heyne Tillet Steel’s highly efficient concrete frame.

We all have our parts to play, and it is incumbent upon designers to educate themselves and to understand the enormous influence they exert – starting with their earliest decisions. Perhaps an overall rule of thumb should be: if you’re not thinking about carbon right from the beginning, you’ve almost certainly not achieved the optimal, lowest-carbon design.

Elaine Toogood, senior director, MPA Concrete and The Concrete Centre