MODERN BUILDING ENERGY CODES AND EMBODIED CARBON: A CASE STUDY OF NEW RESIDENTIAL CONSTRUCTION IN THE NORTHEASTERN UNITED STATES

ABSTRACT In the United States, building energy codes (BECs), specifically the International Energy Conservation Code (IECC), are a primary policy tool for limiting the environmental impact of buildings and advancing decarbonization of the building sector. Historically, BECs do this by regulating and limiting operational energy consumption during the use phase, on the assumption that reductions in energy use equate to reductions in carbon emissions. Following years of incremental improvements, the revisions in the 2021 IECC are expected to generate 9–14% reductions in operational energy use. However, the full carbon impact of buildings includes both operational emissions and embodied emissions, and there is clear evidence that embodied emissions comprise a significant proportion of this total carbon impact. This is particularly true for high-performance buildings with reduced energy use. Despite the ostensible goal of reducing carbon emissions, the IECC does little to explicitly address embodied carbon, and there is a comparative lack of research on the embodied carbon impacts of recent revisions to BECs and the IECC. Using a prototypical single-family residence as a case study, this paper aims to address this gap by assessing the potential embodied carbon impact of compliance with contemporary BECs. The paper finds that the material choices in the exterior envelope can have a significant impact on the carbon use intensity of code compliant residential buildings. In some cases, up-front material carbon emissions account for upwards of 40% and 20% of total carbon use intensity across critical 10- and 30-year timeframes, respectively. Moreover, the analysis shows that low-carbon assemblies that do not meet the current BECs can actually result in lower carbon use intensity over these critical time frames. This paper concludes by arguing that there are relatively simple regulatory options for substantially reducing embodied carbon in code compliant buildings.