Eleven Answers for One Building's Carbon

There is no reliable, standardized method to measure embodied carbon in buildings. A three-level quantitative analysis of 464 datasets from 20 lifecycle assessment databases found that reported embodied carbon for identical building configurations varies by up to 11.5x for steel buildings and 6.5x for cross-laminated timber (CLT), depending solely on which database the assessor uses. Environmental Product Declarations (EPDs) are "not designed to be comparable between products," yet regulators and designers routinely use them for comparative decision-making. This means the same building can appear to be either a climate leader or a climate laggard based on database selection alone.

Buildings account for approximately 40% of global energy-related CO2 emissions. As operational energy efficiency improves, embodied carbon — from material extraction, manufacturing, transport, and construction — becomes the dominant share, representing 50–80% of lifecycle emissions in new high-performance buildings. Cities including Vancouver, New York, and London have adopted or proposed embodied carbon limits, but these regulations are built on measurement systems that vary by an order of magnitude. Policy decisions based on unreliable measurements may incentivize the wrong materials and construction methods.

System boundary inconsistencies plague the field: only 39% of studies address end-of-life or reuse phases, missing 9–100%+ of additional embodied carbon from maintenance and replacement. Sixty percent of investigations originate from only 5 countries, leaving the Global South without representative data. No consistent data exists for fenestration, adhesives, and MEP (mechanical, electrical, plumbing) systems — major building components simply absent from databases. Substituting site-specific datasets for generic databases (e.g., Ecoinvent) changes GWP calculations by up to 95%. Product-specific EPDs show approximately 15% lower GWP than generic data in comparable Norwegian case studies, but the direction and magnitude of this bias varies by region and material.

A unified reference dataset with mandatory system boundary definitions — covering cradle-to-grave including end-of-life — would enable meaningful comparison across studies and databases. Regional calibration factors that translate generic international databases to local manufacturing conditions would improve accuracy without requiring full local LCA datasets. Mandatory disclosure of database selection and system boundary assumptions in regulatory compliance reports would make the measurement uncertainty transparent to decision-makers.

A team could select a standard building design (e.g., a 4-story residential building) and calculate its embodied carbon using 3–4 different databases (Ecoinvent, GaBi, ICE, regional databases), documenting the magnitude and sources of variation across databases for each building component. An architecture team could conduct a case study of an actual building project comparing EPD-based calculations against site-specific data. Relevant disciplines: civil engineering, architecture, environmental science, data science.