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The hierarchy of net zero design

In this blog, Will Arnold discusses the conflict between the need to build and the need to reduce resources, and how engineers can construct whilst keeping the environmental impact to a minimum.

Construction – good and bad

Buildings are a good thing. They bring people together, keep them warm, and give them places to be useful. Buildings raise the world above the social foundation articulated by Doughnut Economics to bring life’s essentials to every person on earth. But simultaneously, the construction, operation and destruction of our buildings has been pushing us beyond our planetary boundaries for quite some time now – and this must stop.

We can’t just stop construction altogether though – as we need more buildings and infrastructure (more so in some parts of the world than others). So instead, we must learn how to construct while minimising our damage to the environment.

Eventually, we must actually start constructing buildings that heal the environment rather than simply damaging it less… but that’s a topic for another post.

Where are the emissions?

Historically, most of the carbon emissions from buildings have been due to their operation (heating, lighting, cooling, etc). However, this is changing. There are plans for reducing these emissions – electrification, insulation, and generation on site – so the largest contributor to a modern building’s emissions is the materials used in its creation – the embodied carbon.

Most of the embodied carbon emissions are due to the construction of the building structure. In fact, the concrete and steel industries combined make up over 15% of all global emissions. And as the structure of a building typically comprises just two or three materials, if you focus on decarbonising these few pieces of the puzzle then you can make very large carbon savings very quickly.

That’s why I believe that the decarbonisation of structures in buildings is one of the most important challenges facing our industry today.

Use less stuff

Most approaches to reducing structural emissions fall into one of two types of action. You can minimise the amount of material that you use (put simply: use less stuff), or you can minimise the amount of carbon released when producing those materials. These also form the two parts of the equation describing embodied carbon emissions:

Embodied carbon = (quantity of material) × (carbon intensity factor)

As a building designer, your priority is the first type of action, or the left-hand side of the equation. You must push to use less stuff. This involves prioritising better use of existing building stock, and then configuring new structures to minimise material use. Our massing, layout and configurations must get more efficient (we often need to convince others to enable this), and then our design methods and utilisations must deliver this with no ‘spare fat’.

This reduction in material is important, because as a building designer, you have little real opportunity to minimise the carbon intensity factor of your materials through material specification – something I explore further in three audio briefings on steel, concrete and timber.

This is why the image at the top of this page – the IStructE’s Hierarchy of net zero design (influenced by PAS2080) – has so much emphasis on using less stuff. This is where most structural engineers have influence and impact, and so this is where the focus should be.

Materials decarbonisation

While the design engineer’s focus should be on using less stuff, material decarbonisation remains an important topic. If you’re reading this as a materials researcher, scientist, producer or R&D investor, then this bit applies to you!

If we are to help deliver a 1.5°C future, then the emissions due to structures in buildings (which I believe to be nearly 10% of all global emissions) need to be halved by the year 2030, and reduce to zero by 2050.

Engineers can reduce the emissions in their structures by a small amount pretty easily (less overdesign), and can start to make some significant reductions with the right architectural backing. I reckon that a 50% reduction compared to business-as-usual is even possible if the client demands it, and when the whole design and construction team pull together.

However, 50% only gets us to 2030. How do we continue our trajectory towards zero? For this, we need lower-carbon materials.

And so, while the Hierarchy of net zero design focuses on using less stuff, there is a parallel challenge to create lower-carbon materials. We explore this further in a paper outlining what we believe to be the R&D needs of the industry.

You can make a difference

It’s a fantastic time to be a building designer – we are some of the few people on earth with the opportunity to make significant reductions in carbon emissions. However, we must put our effort in where it will have the most impact if we want it to really count.

Understanding whether we are using less stuff, or decarbonising materials, is an important first step.

Is it one you are taking yet?


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