Construction is one of the leading industry emitters of carbon emissions. However, there are ways to reduce this footprint and offset the carbon cost of construction projects, which can lead to as much as a 90% reduction in a project’s net carbon costs.
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Construction’s Carbon Challenge
Nearly all buildings represent embodied carbon (sometimes expressed as CO2e). The embodied carbon representation of a building is all of the carbon emissions caused in order to build it. These come from extracting building materials, transporting them, and activity on site.
Some embodied carbon calculations also include the carbon costs of operating the building throughout its lifecycle (warming and cooling, supplying utilities like water and electricity, and so on), as well as the carbon emissions caused during demolition and waste removal when the building reaches the end of its life.
There is a huge amount of embodied carbon in the world’s buildings.
Worldwide, buildings cause a third of all greenhouse gas emissions and make up two-fifths of our total energy needs. In the European Union (EU), the construction industry uses 40% of all new materials and the same percentage of primary energy supply. It also creates 40% of the Union’s total waste every year.
At the same time, the rate of construction is still increasing. The total population is rising, and more people are moving into cities. As a result, the urban population in the world is expected to pass six billion by 2045. This means that our cities will have to grow, and we will need to find more sustainable approaches to construction if we are going to be able to do this without harming the environment even more.
At present, there are insufficient government requirements or incentives for developers to commit to low or zero net embodied carbon targets for construction projects. However, this situation is beginning to change. The Buy Clean California Act, for example, came into force in 2020 and regulates products used for state construction projects like schools and highways.
There are several phases of construction that need to be captured in embodied carbon assessments, and the earliest of these is also by far the largest.
Producing materials including concrete, steel, iron, cement mortar, oil, and non-metallic minerals and then transporting them to sites generates between 82% and 96% of a building’s total carbon emissions.
This means that efforts to reduce the materials demand in construction projects will have a significantly high impact on the project’s carbon footprint. This can be achieved by designing for resource efficiency. This might be achieved with technology like building information modeling (BIM) and computer-assisted design (CAD) software to apply computer processing to maximize efficiency.
Using lightweight concrete in large projects is another way of minimizing their material requirements. Concrete with high ratios of additives like silica fume or fly ash reduce the overall structural load of the building. This means that it requires fewer materials to meet safe load tolerances.
An obvious and important means of reducing material demands from the construction industry is taking the decision not to build. This brings the question of sufficiency into the equation as well as efficiency.
When considering new projects from a sufficiency perspective, planners and developers can limit new projects only to what is necessary. This might include retrofitting or restoring buildings instead of demolishing and replacing them, or constructing buildings with a smaller geographical footprint.
Developers can also use better, more sustainable materials to reduce their projects’ carbon footprints.
Kenoteq is a UK manufacturer of bricks made of up to 90% waste material. This brick contains about 72.5 g CO2e, compared to traditional clay bricks that have about 570 g CO2e each.
Using recycled materials is another good way of offsetting carbon emitted by construction projects. Recycled aggregate concrete is a good example of this. It is made from waste brick, metal, tiles, plastic, wood, glass, and even paper. Untreated, it does not perform as well as conventional concrete in terms of durability and mechanical properties, but there are numerous admixtures available to improve performance including silica fume, fly ash, and meta-kaolin.
Replacing clinker in cement with industrial by-products is another way of reducing its embodied carbon content. Also, Portland cement can be replaced with alkali-activated slag (AAS), which requires a lot less energy to manufacture.
There are minimal carbon gains available from on-site activities required to construct buildings. This is because they generally only make up about 1% to 3% of the project’s total emissions.
Nevertheless, modern building methods like using prefabricated elements can make the building works less energy intensive as well as reduce the total weight of materials required. In one study, it was found that panelized timber frame buildings had about 34% less embodied carbon than traditional masonry constructions.
Economic Carbon Offsets
Another way that buildings could reduce their net environmental impact is by purchasing economic carbon offsets. These are tradable certificates awarded to companies for lowering the content of carbon in the atmosphere, for example through carbon capture and sequestration or reforesting.
Critics of carbon offset schemes say that they merely allow wealthy organizations and states to pass on the burden of environmental responsibility with relative impunity. This may be unlikely to lead to the kind of system and behavior changes (for example, designing for sufficiency) that are required to avert the worst outcomes of the climate catastrophe we are facing today.
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References and Further Reading
Gurgel, A. (2020). Carbon Offsets. [Online] MIT Climate Portal. Available at: https://climate.mit.edu/explainers/carbon-offsets (Accessed on 12 September 2022).
Jones, E. (2020). 5 Ways to Reduce Embodied Carbon on Your Next Building Project. [Online] Project Sight. Available at: https://projectsight.trimble.com/reduce-embodied-carbon-on-your-next-building-project/ (Accessed on 12 September 2022).
Pilkington, B. (2021). Reducing the Construction Industry's Footprint with Revolutionary Bricks. [Online] AZO CleanTech. Available at: https://www.azocleantech.com/article.aspx?ArticleID=1251. (Accessed on 12 September 2022).
Sizirici, B., et al (2021). A Review of Carbon Footprint Reduction in Construction Industry, from Design to Operation. Materials. doi.org/10.3390%2Fma14206094.
Shin, B., et al. (2020) Mitochondrial Oxidative Phosphorylation Regulates the Fate Decision between Pathogenic Th17 and Regulatory T Cells. Cell Reports. doi.org/10.1016/j.celrep.2020.01.022.
Pesheva, E. (2020). Tackling Coronavirus. [Online] Harvard Medical School. Available at: https://hms.harvard.edu/news/tackling-coronavirus (Accessed on 26 February 2020).