On the route to a carbon neutral world, construction can’t be bypassed.

Knowing that, we have to go down the rabbit hole to find the drivers of CO2 emissions and identify ways to avoid these emissions. Spoiler alert: it’s not as easy as plugging out conventionally generated electricity and plugging in renewables.

Here are my 10 slices on why reducing CO2 emissions in construction isn’t a plug and play game:

1/ Yonsei University conducted a study in which they measured CO2 emissions during the construction phase of a building. According to their research, 2.4% of CO2 resulted from material transportation while 4.2% of CO2 was produced during on-site construction. However, the majority of emissions — 93.4% — was coming from the production of building materials used to build.

2/ Ergo: Optimizing supply chains and operations on-site is advisable from an economic point of view. But: it doesn’t move the needle on emissions. The main lever to reduce emissions in the construction industry are building materials.

3/ And: Within the subset of building materials, steel, cement, and other mineral materials have the largest impact, making up more than 50% of the CO2 emissions in the construction industry

The impact becomes even more tangible when looking at absolute numbers: the production of one ton of steel emits ~1.8 tons of CO2 while the production of one ton of cement releases ~0.58 tons of CO2. And: in 2018 ~4bn tonnes of cement and ~900mn tonnes of steel were used in the construction industry.

4/ And: There are 3 ways to cut down these emissions:

Choice of materials: use carbon-neutral substitutes

Amount of materials: use materials more efficiently

Production of materials: decarbonize building material’s production

5/ Ergo: When assuming that we can’t scale down the use of cement and steel to zero, we have to find ways to decarbonize their production processes.

6/ And: Both production processes have similar key characteristics.

Embodied emissions: During the production of the materials, embodied emissions are released through chemical transformations of the feedstock. On average, these emissions make up ~45% of CO2 emitted during the material production.

Process emissions: The processing of the feedstock into the final product requires temperatures of up to 1500 °C. The combustion of fossil fuels needed to generate the heat accounts for ~35% of CO2 emissions during the material production.

Production assets: The manufacturing plants needed to produce the materials have lifespans of more than 50 years. Additionally, processes have been optimized and fine-tuned for more than a century. A change of one factor in the process often requires multiple adjustments of other factors.

7/ And: These key characteristics make it particularly difficult to decarbonize the production processes.

Embodied emissions can’t be abated by using different kinds of fuels. To avoid these CO2 emissions, production processes would need to be fundamentally redesigned, eg. by adding CCS to the process.

To reduce process emissions alternative fuels can be used as a substitute for fossil fuels. Switching to carbon-neutral electricity, however, would require a major redesign of the production processes as well.

Long life span of assets make it economically challenging to fundamentally redesign the manufacturing plants.

8/ Ergo: Decarbonizing the production of building materials is highly challenging but technically achievable through a combination of different solutions.

9/ But: the most promising solutions (such as CCS or the use of hydrogen) are currently in pilot stage and not available at industrial scale.

10/ Ergo: Turning today’s building materials carbon neutral isn’t a plug & play game. It’s a complex challenge that forces us to think of more than just a carbon neutral version of what we do today. We have to rethink use-case specific choices of building materials and ways to use materials more efficiently than we currently do.

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Sources:

• Min-Seop Seo et al 2016, On-Site Measurements of CO2 Emissions during the Construction Phase of a Building Complex
• Edgar G Hertwich et al 2019, Material efficiency strategies to reducing greenhouse gas emissions associated with buildings, vehicles, and electronics
• McKinsey, Decarbonization of industrial sectors: The next frontier
• OECD, Perspectives on steel by steel-using industries
• UN Environment, Global Status Report 2017