Practitioners interested in reducing the embodied carbon of buildings are likely familiar with weighing the impact of different materials, like mass timber or low-carbon concrete. Low-carbon construction, however, has not been on many people’s radar.
“I don't think people up until now even thought about fossil fuels being burned” on the jobsite, Oliver Atkinson, sustainability engineer at Sellen, told BuildingGreen. The few existing estimates, based on a handful of case studies and simplified assumptions, suggest the impact is relatively small—1% to 5% of the total lifetime carbon, or around 7% of the upfront embodied carbon of a building.
But once you start looking, said Atkinson, “Fossil fuels are being burned everywhere.” Mark Chen, sustainability manager at Skanska, agreed: “Anything that involves big, yellow, iron pieces of equipment” will account for significant emissions, he contends.
Recent findings from construction companies that are tracking these data on projects indicate that construction emissions account for 10% to 20% of upfront embodied carbon. And an economy-wide input-output analysis suggests they could be as much as 30% of upfront embodied carbon. These figures point to the possibility that the construction process emits more than we thought, representing a bigger piece of the embodied carbon pie—and, more importantly, growing the size of the pie altogether.
In this report, we dive into the origins of current estimates, explore why they might be low, and compare them with findings from actual project-level tracking. Though we will focus on greenhouse gas emissions (using the term “carbon emissions” as shorthand for CO2 equivalent), it’s important to remember that construction emissions also contain many other criteria pollutants, which pose risks to human and ecosystem health.