Exploring the significance of transportation emissions in upfront embodied carbon in buildings

Addressing embodied carbon associated with building materials is urgent. Transportation (A4) emissions are sometimes neglected (or incorrectly calculated) in relation to the materials' product stage (A1-A3) and a building's use stage (B1-B7) emissions. We present a comprehensive model for considering transportation emissions in individual building projects to determine their significance in upfront (here A1-A4) embodied carbon. Transportation scenarios are presented for an illustrative case study of a multifamily residential building in Oakland, California, although the methods described herein are applicable to any location. Material emissions are extracted from site-specific environmental product declarations (EPDs) and are compared to transportation emissions calculated based on direct operational emissions from transporting the goods from the EPD's stated manufacturing location to the project site and embodied emissions from transporting the goods, from manufacturing the delivery modes (vehicles, freight trains, cargo/container ships) and constructing the delivery infrastructure (roadways, railways, port terminals). Relative to three defined scenarios (Lowest Materials Emissions, Closest to Project Site, Furthest from Project Site), transportation emissions account for anywhere from very little (close to 0 %) to over 80 % of upfront embodied carbon, depending upon the specific material and manufacturing location. Results differ when transportation is electrified or uses biofuel. A blanket policy on demanding locally produced materials might actually increase A1-A4 emissions. This study serves to refine how different life-cycle stages are considered in Whole Building Life-cycle Assessments (WBLCAs). Future research should continue to explore the efficacy of current WBLCA methodologies, particularly in estimating upfront embodied carbon. © 2024