Guiding Decarbonizing of the Built Environment: Trends, Methods, and Approaches for Carbon Benchmarking in Buildings

The built environment is a major contributor to global greenhouse gas emissions and urgently requires decarbonization. Despite the decline in operational carbon emissions, which continue to fall as energy-efficient buildings rise, embodied carbon (EC) emissions from material extraction, production, and construction have become increasingly prominent, accounting for an increasing share of total building emissions. Establishing a benchmark value for buildings is essential for assessing, comparing, and mitigating emissions in new construction because it helps set goals, evaluate performance and resource efficiency, promote sustainable building practices, and lay the groundwork for decarbonizing the urban built environment. Globally, building carbon benchmarks are developed using life cycle assessment and statistical methods, whereas whole-life carbon assessment frameworks are increasingly adopted with regulatory integration. However, broader applicability remains constrained by methodological inconsistencies. This research reviews existing benchmarking studies and identifies discrepancies via semi-systematic and critical analyses. The results reveal that 81% of benchmark studies apply bottom-up approaches, and nearly 88% focus on residential buildings. The range of benchmark values for residential buildings using the bottom-up approach varies from 1.3 to 63.9 kg CO2e/m2/year, whereas the top-down approach ranges from 1.2 to 27 kg CO2e/m2/year. The overall range is 1.2 to 92.5 kg CO2e/m2/year, reflecting substantial variation due to variable scopes, typologies, modeling approaches, and data sources. This research highlights the urgent need for standardized benchmarking methods to ensure comparability across studies, enable effective policy implementation, and support decarbonization. Additionally, this study proposes a framework for establishing EC benchmarks and strategies that promote low-carbon, resource-efficient urban development.