One of the key questions when it comes to sustainability and the construction industry is what proportion of the emissions associated with a building can be ascribed to the materials used in its construction versus the energy used to heat and light the building during its life.
Many factors and assumptions can affect the conclusion one comes to when trying to tackle this question, including the lifetime of the building itself, the future state of our electricity grid, and whether it matters when during a building’s life the emissions are generated.
In this post, we examine a statement in the recent CEMBUREAU roadmap (2020) shown in Figure 1 below that “72% of CO2 total emissions related to an average building come from the energy used during its working life”. This seems to suggest that embodied carbon makes up a proportion of the impact than other reports might suggest (Material Economics, RICS, LETI).
The source quoted by CEMBUREAU is a World Green Building Council report from 2019, which states:
“Currently, buildings account for 39% of energy related global CO2 emissions2, demonstrating the importance of the building and construction sector in fulfilling these ambitions [to deliver the Paris Agreement]. Of this sector contribution, 28% comes from operational carbon with 11%3 arising from the energy used to produce building and construction materials, usually referred to as embodied carbon”
The WGBC report states that buildings account for 39% of energy related global CO2 emissions, and that of this contribution 28% comes from operational carbon, and 11% from the energy used to produce construction materials. Twenty-eight percent out of 39% gives the 72% operational emissions quoted by CEMBUREAU.
However, the key phrase is that these are energy-related CO2 emissions. As a footnote to the WGBC article states, this does not include any process–related emissions. In the case of cement, emissions from the chemical process of clinker production make up approximately half of total emissions. Excluding these from the embodied emissions of the building is misleading, particularly as the CEMBUREAU report refers to “total emissions”.
The reader of the CEMBUREAU report is left with the impression that embodied carbon is much less important than operational carbon, because the numbers used are not telling the whole story. When examining the operational to embodied carbon split of construction using concrete, we must not ignore the process-based carbon dioxide emissions.
