Civils and carbon: must try harder
Designers and specifiers of civils works are missing opportunities to reduce the carbon intensity of projects. Is it laziness, or are there deeper issues at play? asks Andy Yates
There is now enormous focus on minimising carbon in building structures and operationally, but frequently the design and specification of civils works seems to be overlooked. Before I go any further, I should say that I’m using the phrase “civils works” to refer to the external works, hard landscaping and drainage works on your normal, run-of-the-mill type project, where the civils items are often buried or hidden, may be seen as secondary to the main building or project, or just a fairly standard public realm improvement.
The civils aspects of these projects frequently have large quantities of materials generated from a few typical details, often simply copied from previous projects. Think of surface-grade car parking, often just a detail or two for the kerbs and the surfacing build-up, but the actual works cover a large area with significant amounts of materials. Generally, this is all simple stuff and therefore not really thought about, particularly from a carbon perspective. However, small changes to the design approach and material specification can have big impacts because of the quantities of materials used. Bigger changes could have a far greater impact.
For example, do we need to specify this particular kerb? Is there an alternative with lower carbon impact or lower cement content? Do they need to be made from concrete, or could we use natural stone or timber edging? Could we reuse reclaimed kerbs instead? Does the haunching need to be that concrete mix or could it be weaker with less cement? Do we need concrete surround to the manholes? Is the surfacing build up over-designed for the actual vehicle usage? Can we use site-won material for the sub-base? Can we specify recycled asphalt? Or actually, do we even need kerbs at all?
Such thinking can have significant effects on the carbon intensity of our projects, yet all too frequently we aren’t even in the mindset to explore what could be achieved.
Data to inform such decisions is now readily available; we just need challenge ourselves to do the research
We also need to think harder and better understand the impact of the items we are specifying. For example, maybe natural stone kerbs sourced from overseas have a higher carbon intensity than locally sourced precast concrete kerbs. Data to inform such decisions is now readily available; we just need challenge ourselves to do the research.
In my opinion, there is a lack of sustainability ambition in these civils works. It is all too easy to churn out a few standard details and specification clauses and not think too hard about the carbon impact. Yes, we often think about sustainability in terms of the impact on issues such as flood mitigation or control, but don’t necessarily push ourselves to think harder and aim higher. We can hide behind standards or typical details, but these are changing – why can’t we challenge the client to do better? It is too easy to overdesign something (“that works, so I’ll just use it everywhere”) or just copy something from a previous project (“well, that’s the way we’ve always done it”).
At Webb Yates Engineers, on one of our current large-scale residential projects in Berkshire, the excavated material has been reused as structural fill and capping in the external works. This required us to push the project team and contractor to even consider it, and testing to prove that it was suitable, but we have now avoided the need to remove and import a large amount of material. Similarly, we are reviewing and updating all our external works standard details, as well as adding and amending our specification clauses, to reduce the carbon intensity of our projects without compromising on performance.
It is all too easy to churn out a few standard details and specification clauses and not think too hard about the carbon impact
As construction industry professionals, we are good at problem-solving – it’s what we all do every day. So every time we pick up a client’s brief, a preliminary design, a specification, a set of detailed design drawings or a contractor’s proposal, we should say to ourselves and the project team, “the problem here is that there is 25% too much carbon – let’s fix it” (or whatever the actual percentage is). Just by looking more closely at what is proposed with the mindset of reducing carbon, we can have a huge impact. If at each step we reduce the carbon by 25%, we will have made a 75% saving across the whole project. This is the mentality and approach that we all need to have.
We must change our day-to-day thinking and move away from the tendency to choose the easy, obvious, traditional solutions for civils works on our projects. Let’s think more ambitiously, more creatively and more resourcefully, and ultimately, benefit our places and the planet.