The built environment, encompassing the construction and operation of buildings, highways, bridges, and other infrastructure, contributes to nearly 40 percent of global greenhouse gas emissions.
Ming Hu, the associate dean for research, scholarship, and creative work in Notre Dame‘s School of Architecture, emphasizes the need to address embodied carbon in existing buildings, urging policymakers and industry leaders to take a comprehensive approach to reducing emissions beyond just focusing on the construction of new energy-efficient buildings.
Embodied carbon is a critical factor in the environmental impact of products and buildings. It encompasses the greenhouse gas emissions associated with the entire lifecycle of a product, from material extraction to disposal. Materials like asphalt, concrete, and steel have particularly significant environmental consequences in the construction industry.
Assessing the impact of embodied carbon in the built environment has been challenging due to data limitations. To address this gap, Hu and Siavash Ghorbany, a graduate student at Notre Dame, have developed a new method to analyze the embodied carbon in over 1 million buildings in Chicago.
Their recently published research establishes 157 different architectural housing types in the city and introduces a groundbreaking visual analysis tool for evaluating embodied carbon at a detailed level. This tool can provide valuable insights for policymakers aiming to strategically plan for urban carbon mitigation.
“Before, it was often difficult to visualize this concept and to make a case for why we want to preserve and reuse existing buildings,” Hu said. “We feel this is a more clear, direct way to help the policymaker or layperson make informed decisions. If I were the mayor of Chicago, I could look at this and say, ‘OK, before I tear down this building, I have to think twice because there’s already a lot of carbon embedded in this structure. Do I want to retrofit and reuse this building, or do I want to knock it down and build new, which will increase the overall embodied carbon?’”
Through their research, Hu and Ghorbany have pinpointed areas with high emissions and specific building types in the city, providing valuable insights for urban development stakeholders. Their findings reveal that extending the average lifespan of buildings to 75 years and reducing their size by 20% could result in a significant two-thirds reduction in carbon emissions.
Hu strongly emphasizes that based on her research, there is no scenario where demolishing an existing building to construct a more energy-efficient one makes environmental sense.
“If we look at the building’s entire lifespan, renovating the existing building has significantly lower carbon emissions over its whole life cycle, including operational and embodied carbon,” said Hu, who is also an affiliated faculty member in the College of Engineering. “That’s because the ‘payback period’ for constructing a new building is typically 20 years due to the high level of greenhouse gas emissions created by its construction. So, if we can extend a building’s life cycle to 70 or 80 years, then reusing the existing building definitely makes more sense.
“We should always reuse existing buildings. The real question is just to what extent we want to renovate and retrofit them.”
Hu and Ghorbany chose Chicago for several compelling reasons, including its proximity to Notre Dame, rich architectural history, and its ranking as the 8th highest city in the world for greenhouse gas emissions. They aim to expand their project to assess embodied carbon in cities nationwide.
Funded by the National Science Foundation, the researchers leveraged machine learning and artificial intelligence to compile a comprehensive dataset for their analysis.
By integrating various existing datasets, such as the National Structure Inventory and Cook County Open Data for Chicago, they categorized and coded the geolocated data based on different features like structural materials and roof type. Next, they calculated the total embodied carbon of each building by multiplying the housing type’s baseline emissions with its footprint.
Ghorbany, also a graduate scholar at the Lucy Family Institute for Data & Society with an undergraduate degree in architecture, emphasized the importance of developing an accessible, interactive mapping tool to visualize their findings.
“Our goal for the end product was to create a user-friendly way to access and engage with this data,” he said. “We created this one so that you can try different scenarios by selecting which types of archetypes you want to see and filtering them by year or types of emissions. I hope that in the future, cities will be able to use this tool to reduce their carbon emissions so that we can help reduce climate change and the impacts we’re seeing from it.”
Hu agreed and noted that the potential benefits of this research are not only environmental but also cultural.
“First, it is crucial that we have a clear inventory of the embodied carbon in our built environment,” she said. “It’s something we’ve never had before and still don’t have nationwide. Once we have that, we can make informed decisions about how to reduce our carbon emissions, in part by extending the lifespan of these buildings.
“And, in addition to the environmental benefits, there is social and cultural value to preserving these buildings that are part of the architectural character of the city.”
Journal reference:
- Siavash Ghorbany and Ming Hu. Urban embodied carbon assessment: methodology and insights from analyzing over a million buildings in Chicago. Carbon Management, 2024; DOI: 10.1080/17583004.2024.2382993
