The building design and construction industry is increasing focused on the embodied carbon of building materials and construction. Embodied carbon refers to carbon dioxide (and in many instances the CO2 equivalent from other emission sources) that are released to the atmosphere during the manufacture, transport and construction of building materials, along with end-of-life emission impacts (when specified).
For example, if concrete is specified for a building, then the embodied carbon comprises that which was emitted for manufacturing and delivering that concrete.
The debate over how much embodied carbon really matters
Unlike operational carbon emissions, which can be reduced over time with energy-efficient renovations and the use of renewable energy, embodied carbon emissions are locked in place as soon as a building is build.
Advocates of low/no-carbon buildings cite the anticipated average of 62 billion square feet of new construction to occur globally every year over next four decades as a major carbon emissions source that needs to be more effectively addressed if we have any chance of reducing the proportion of global carbon emissions from the buildings—which currently stands around 40 percent.
Meanwhile, contrarians cite that over the 60-year life of a building, the embodied carbon impact is but a drop in the bucket when consider the building's total carbon impact—for example, in a commercial structure, the embodied carbon may only account for around 5-10 percent of the total carbon contribution. The vast majority of the carbon impact comes from operations.
Near-term importance of embodied carbon
The crux of the debate regarding the global warming potential from building construction hinges on one simple measurement: time.
There is a temporal consideration that seems to often be buried in the embodied carbon discussion. Architecture 2030 is an advocacy group that calls for carbon-neutral building operations by 2030 (i.e., using no fossil fuel greenhouse gas-emitting energy to operate). Increasingly, the group is focusing on embodied carbon as well because, according to their data, embodied carbon will be responsible for almost half of total new construction emissions between now and 2050.
Simple analysis for understanding relative impact
To better relate to this issue, I decided run an analysis to compare the embodied and operational carbon contributions from one of my recent institutional projects. I chose a roughly 100,000-square-foot multidisciplinary research and classroom building on a major university campus in Indiana. This project is pursuing LEED certification and has been modeled for both life-cycle environmental impacts as well as operational performance.
The analysis yielded the following:
- Modeled embodied carbon equivalent impact: 499 kgCO2eq/m2, which is consistent with figures from Embodied Carbon Benchmark Study by K. Simonen, et al. (2016), which found nearly 75 percent of office buildings to be less than 500 kgCO2eq/m2.
- Modeled annual energy consumption from electricity, district steam, and district chilled water (from an electric-driven chiller) accounted for 280 kgCO2eq/m2.
- As the figure below demonstrates, in the near term of 10 years, embodied carbon accounts for a much greater proportion—roughly a third—of the building's carbon equivalent emissions.
- Over the course of a presumed 60-year life-cycle (hopefully the building will last much longer than that), the initial embodied carbon equivalent impact from the structure and envelope accounts for less than 6 percent of the cumulative carbon impact of the building.
A couple of qualifiers/clarifications:
- This simple analysis considered year-after-year energy consumption—and consequential carbon impacts—to be the same. In reality, it is likely that a greener campus infrastructure would be established over the life of the building and the utility's electricity would be based on a greater amount of renewable energy sources.
- The embodied carbon in this analysis only accounts for the building structure and envelope. The interiors and mechanical systems are not accounted for.
- The project would likely undergo at least one mechanical system change-out and several renovations of various scales over 60-years. This would all increase the proportion of total embodied carbon from construction.
The take-away here is two-fold:
- If we are to achieve near-term goals for reduced carbon emissions from the building sector, embodied carbon matters a great deal.
- This simple analysis underscores the virtue of avoiding most of the embodied carbon emissions of new construction by utilizing the existing building stock. Sensible retrofits and renovations is an extremely impactful strategy in reducing global carbon emissions from the building sector.
Embodied vs Cumulative Operational Carbon Impact by Year.
Illustration courtesy of author.