Decarbonising our building materials

Carbon.

A word that’s becoming increasingly used in our day to day vocabulary and one that will determine how we design well into the future. The U.N.’s Intergovernmental Panel on Climate Change (IPCC) estimates that we as a global community have roughly ten years to reduce our greenhouse gas emissions if we want any hope of keeping average global warming to 1.5 degrees Celcius. That isn’t much time, and we all need to act now and act fast.

Structural engineers work with materials like concrete, steel and timber every day, and these impact on the environment both positively and negatively. Together these materials form a big part of our urban landscape and enable us to live, work and play – giving us access to healthcare and education, creating healthy, productive offices and beautiful places that we want to be in. The social impacts are easy to appreciate because we think about how our designs relate to the world around us and strive for positive outcomes for our communities.

But what about the environmental impact? What about the hidden carbon emissions associated with sourcing, producing and using those materials – the “embodied impacts”? How much is that shiny new office really going to cost in environmental terms?

Thinkstep, on behalf of the New Zealand Green Building Council, recently released a report that looks at the materials that contribute to the bulk of embodied greenhouse gas (GHG) emissions in buildings. ‘Under construction – Hidden emissions and untapped potential of buildings for New Zealand’s 2050 zero carbon goal’ puts forward practical short-term (2020 – 2025) and long-term (2030 – 2050) decarbonisation strategies to help us meet our carbon reduction goals.

‘Under construction’ focusses on three building forms: residential, office and warehouse. The report assesses the impact of commonly used materials on the carbon footprint of each building type; finding that concrete, steel and aluminium have the most impact across all three building types, with plasterboard and timber also contributing significantly to residential building footprints.  

Taking into account the production of materials, the energy source for production and the optimisation of design, Thinkstep proposes five key strategies:

Short-term (to 2025)

1. Concrete – replace 30% of cement with supplementary cementitious materials (SCMs)
2. Aluminium – source from smelters powered by renewable energy
3. Steel – use optimisation in steel design to reduce steel quantities

Long-term (to 2050)

4. Cement – replace 40% of coal with alternative fuels
5. Steel - replace coking coal with bio-charcoal or use hydrogen technology

The report also notes some of the barriers to achieving these goals. It points to the availability of materials and the high costs associated with procuring scarcer materials. Annual global cement production, for example, is approximately five billion tonnes, whereas only 750 million tonnes of SCM fly ash is produced every year. Another limiting factor to decarbonisation is the reluctance of some specifiers to challenge the original building specifications by proposing lower carbon alternatives.  

So, what does this mean for the building construction industry?

The report sets out some clear strategies for achieving zero carbon in the sector, but accomplishing the results is going to take a monumental effort and focussed collaboration across the board. We need to come together as an industry regardless of our professional background or which company we’re employed by and work out how to decarbonise the built environment. By working together, we will learn faster, design better and enable systemic change.

Climate change is happening and, for some, measuring impact could be scary and uncomfortable. The good news is that despite this, we are starting to see a global shift. The construction industry is starting to consider the embodied carbon impacts of design decisions. Guidance in reports like ‘Under construction’ provide us with some clear areas of focus, but we need to be courageous too - agree the goal, reach out to our peers and get stuck in.