Lowering embodied carbon: five trends in building design and construction

To achieve net zero in the built environment, it is essential that embodied carbon is reduced. But as many low carbon materials are still far from widely available, taking consistent action now seems both costly and infeasible. How should we think about lowering embodied carbon in construction, what are the complexities and what strategies exist to reduce it right now?

Why is lowering embodied carbon so important?

‘Lowering embodied carbon is absolutely critical to net zero’ explains Martha Dillon, Sustainability Consultant at Buro Happold. Embodied carbon is the emissions associated with materials and processes over the whole lifecycle of a building. ‘The embodied element of carbon is enormous. In the UK it’s about a third of emissions from the built environment. As our power supplies decarbonise, the embodied energy could end up being a really huge proportion of remaining emissions. We work in a joined-up sector so we should be thinking about all the elements of carbon that arise from our projects and activities.’

‘I’ve described it as the ‘dark side’ of the construction industry’, explains Dr Zaid Alwan, Senior Lecturer, Department of Architecture and the Built Environment at Northumbria University. ‘It’s something that we can’t really see, we can’t really visualise and therefore its impact is enormous’. As he explains: in comparison to the aviation industry, which contributes roughly 2-3% of global emissions, embodied carbon, specifically steel and concrete production, contributes about 8-10% of global emissions.

Assess, refine, adapt and standardise

Various standards and measurement practices exist for looking at embodied carbon, explains Dr Zaid. As well as measuring embodied carbon manually through a spreadsheet, there are off-the-shelf tools available, some companies have their own in-house approaches, and there are also digital plug-ins, which work with BIM360. Martha says, ‘In terms of specific tools, there are some that are more appropriate for concept stages as they are a bit simpler, but if you’ve got detailed models there are plug ins you can use. I’d move away from the tool being the answer. The tool is a way to iterate the design, but it is not going to give you a lower embodied carbon figure by itself.’

Doing something to lower embodied carbon is what is critical, and this requires a specific set of skills, says Dr Zaid. He explains the need to take a phased approach, ‘where you do your assessment and then you act upon it: you redesign and find your substitutions and alternatives.’

Neil Pennel, Head of Design and Innovation at Property Solutions at Landsec says, ‘the problem for embodied carbon is that accuracy and comparability between assessment done. International standards drive consistency across the whole global economy, which is great, because we get materials from across the world in the process of building. But ultimately, if you’ve done an assessment on your building, whatever method or data you’ve used, you’ve got a starting point to compare against.’ And from that relative basis, you can begin to drive down the embodied emissions in your practice. ‘Over the decade that we’ve been assessing carbon in our buildings, those assessment approaches have become more normalised, people have collaborated and the databases available are much better.’

Circular construction: from cradle to cradle

‘It’s about designing something really well, and using it many times going forward’, explains Neil. ‘There’s some really positive things on the horizon, but in the meantime we need to take all the practical steps. To design with the minimum amount of materials, to minimise the carbon footprint with the supply of the materials you choose, and we should definitely be looking at how or where buildings can be repurposed or their life extended. We need to be designing for longevity and future deconstruction and reuse of those materials. Design for manufacture and assembly is driving thinking about reducing waste, minimising material use, and coming up with solutions that you can re-apply time and time again.’

There’s no one-stop substitution solution, but small steps can have dynamic effects

While the construction industry is starting to talk about embodied carbon more, the panellists report they are not seeing the pace of change that’s needed in the sector. ‘At part of our COP26 initiatives, we need to be looking at not just net zero operational carbon, but also net zero total carbon, and we can only do that by starting immediately’ says Dr Zaid.

Cement is a huge consumer of energy. It is possible to find alternative materials with lower EPD values, explains Dr Zaid, but the sector isn’t there yet in terms of supply and development. ‘You can’t just look at that independently, you need to look at it as part of re-engineering, redesigning so that you’re using less of the concrete and that’s critical. Timber-framed construction is something we should do more of. We also need to consider the impact of the components we use’, he says, such as the embodied carbon in heat pumps.

Martha says: ‘it’s really challenging to do if you’re just doing like-for-like material substitutions. Re-engineering is needed at a more fundamental level. We have vacancy rates across the world: structurally sound buildings that are not used. How do we optimise the use of the building stock we already have? How do we maintain the building stock so it lasts longer and we don’t need to demolish? That’s the missing link, and there’s a massive opportunity to be re-imagining how we use the spaces we already have. We can’t keep going to material substitution as a solution when material substitution does not mean net zero yet. We need a combination of approaches.’

A problem that that needs holistic action

‘We’re starting the measure it more accurately, and that consistency will build as we get better at it and these tools develop’, says Martha. ‘But its essential we remain focused on the goal, which is to completely remove emissions: to do that collectively and take responsibility across the supply chain. We should focus on strategies that broadly work, and not take too long on finding the perfect accounting tool and leave those strategies too late.’

‘Once you start doing that relative assessment’, explains Neil, ‘you want to find out: of the suppliers, who can do the best job’. As the industry moves forward, companies in the supply chain will start to measure embodied carbon. The data will become more accurate, making it easier to regulate in future. ‘It’s an area that has improved significantly over the last decade, and will be unrecognisable in 10 years’ time’, says Neil. 

Neil explains, ‘Designers need to think about how the building is being built when they are doing their design. This is so important. The design for manufacture and assembly approach forces you to do that. When you understand what the constraints are, you can design around those constraints, so you’re able to use lower embodied carbon solutions. It’s about challenging your supply chain as well. It means a lot of new thinking and new approaches.’

Cost follows carbon

As Neil explains, steel from one supplier could be lower carbon than the typical average for a number of reasons. It could be much closer to your site so there’s less transport energy, it could be the methodology used to smelt the steel or the amount of recycled steel used. ‘When you do your assessments, you should look across all of those things’, say Neil. ‘Quite often you find that cost follows carbon: the more energy intensive a product is, the more likely it is to be expensive. So it doesn’t have to be a trade-off financially. It’s about interrogation and competence.’

And this is true for social and environmental costs, as much as economic. ‘What sometimes gets lost in conversations about net zero, is that there’s also a huge environmental damage and social impact associated with high carbon materials we’re using.’ Explains Martha. ‘We talk about waste and pollution as throwaways, or co-benefits, but there’s a very real impact of the materials we use today. Change towards net zero is also an opportunity to clean up the sector more broadly.’