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07 December 2020

What is Embodied Carbon?

By Anneli Tostar 

At a glance

Whilst most of the focus on “green building” has been about converting towers, offices and everyday infrastructure to using renewable power, this is only half of the story. The materiality and composition of buildings is equally as important when accounting for architecture’s carbon impact. This S & S decoded feature evaluates the strategic importance of accounting for embodied carbon in construction and architecture. It gauges the environmental toll of key materials, shares the latest innovation research and assesses the circular models applied to new infrastructure. Finally, it reviews the necessary investments and industry collaboration required to design climate resilient cities and landscapes.  

In focus

If you’re reading this, there is a high probability you are well acquainted with the impact of greenhouse gas (GHG) emissions on everyday life. Whether that’s reduction in meat consumption, global travel or the use of renewable energy in our homes, cutting carbon through everyday decision making has become the norm. But, what about the carbon associated with producing or homes in the first place?

What is embodied carbon?
Embodied carbon is the carbon that’s associated with the production process of a single object. This applies to everything from toothbrushes to bridges, however this article in particular focuses on buildings.

The typical building is made up of three main materials: concrete, steel, and glass. Unfortunately, these three materials are extremely carbon-intensive to produce. For many commercial buildings, close to a quarter of their carbon impact can be attributed to the materials they are made of. As the electricity grid continues to decarbonize, this proportion will increase. Concrete alone makes up 8% of global GHG emissions, with a footprint of 600-800kg of CO2 / ton of concrete. That’s more than air travel and the fashion industry combined.

Mike Berners-Lee’s 2020 edition of “How bad are bananas?” sets out that for a 25kg bag of cement you could accrue the following:

  • 1. 9kg CO2e for one ‘green cement alternative’

  • 2. 17kg CO2e for an industrially trialled low-clinker cement

  • 3. 24kg CO2e global average ordinary Portland cement

Why is constructing buildings so carbon intensive? Derived from sand, both concrete and glass are fired in energy intensive giant kilns. Whilst steel isn’t made of sand, it does require heating at notably high temperatures. Distribution and transportation are also factored into the impact of these materials which further explains their carbon intensity. For example, the main component of traditional concrete, cement can only be manufactured from certain types of sand, which are shipped from all over the world in an unnecessarily wasteful manner.

The below graph demonstrates the carbon intensities of the most common building materials:

https://www.sciencedirect.com/topics/engineering/embodied-energy 

It can be seen that the wood is actually a negative number, which on initial inspection may appear confusing. Don’t you have to cut down trees to harvest wood? Isn’t that bad? This is true however carbon isn’t actually released from wood unless it decomposes (or burns), so by using that wood for a building you’re essentially “trapping” the carbon there, too. That is, as long as the “end of life” process for the building is carried out responsibly. If the building is simply demolished rather than disassembled, the carbon is no longer trapped. The same rules apply if the building burns, which is one reason why it’s important to use timber that has been fire-treated.

Innovation & research

Currently, much work is going into creating lower-carbon alternatives to traditional concrete and glass, the two materials that are proving to be unavoidable even if most of a building is made of wood. Across the globe, concrete is being innovated from construction waste materials. Central Concrete in San Jose, California is experimenting with concrete that can  store carbon. Resent research at the University of Tokyo has discovered that adding waste wood to recycled concrete has strengthening properties. Elsewhere in India, moves from key industrial organizations like Dalmia Cement are setting a new standard as they have committed to becoming a carbon negative company by 2040. The future landscape for building design is constantly evolving with researchers recently uncovering a way to make solar panels transparent, to make windows serve a double purpose.

Tackling the carbon intensity of buildings is also aided by the value and attention given to making infrastructure more circular and turning waste into valuable resource. British Land recently refurbished their headquarters in London with façades that were reclaimed from the old building, using a “pop-up” factory nearby. Another case study of circular building in action is Triodos Bank’s headquarters in the Netherlands, which was built using 165,312 screws so that it can be disassembled.

And as much as 84% of steel used in the U.K. is at least partially recycled, lowering its carbon footprint significantly. Metals like steel, although carbon-intensive to produce, can be recycled ad infinitum, unlike other materials like plastic.

Final thoughts

Building for the future is not without obstacles. By 2050, the global population is expected to grow by 2 billion people, with much of this growth happening in the developing world. Climate change will exacerbate migration to land on higher terrain, predominantly cities,  where increased demand for structures such as apartment buildings, offices and communal space will prevail. Indonesia’s movement of the capital from Jakarta to Kalimantan in Borneo is a prime case of this. So, the question of WHERE to build is almost as important as WHAT we build with.  

Architecture and building infrastructure represent a long-term investment in the future. If designed strategically with climate challenges in mind, buildings should endure several decades but investors must be prepared to upfront the initial costs. A recent study by the UK Green Building Council has shown that constructing offices to net zero carbon standards will cost 8-17% more per m2 than traditional building techniques.

To move at pace, real estate developers and owners should collaborate with the entire supply chain and work to prioritise efficiency as well as the use of sustainable materials in developments and retrofits. Developers who are negligent of green materials face international regulations on embodied carbon.

Constructing cities and buildings in a way that doesn’t harm the planet is challenging but not impossible. Through collaboration and dedicated innovation and research, we can work to achieve Sustainable Development Goal #11.