Energy Code Compliance in Modular vs. Site-Built Multifamily Buildings: A Field Study Across Four Climate Zones

Prefabrication in a controlled factory setting may improve the energy performance of modular buildings compared to traditional site-built facilities. However, few studies report empirical evidence to support this premise in full-scale operational buildings. Since energy efficiency standards in the United States are driven by building code, the compliance path chosen and field verification through site inspection, an investigation of how site-built and modular projects satisfy code requirements is critical to understanding long-term energy consumption. Therefore, this study investigated and compared Energy Code Compliance (ECC) among 55 commercial multifamily buildings (25 modular and 30 site-built) in four American Society of Heating, Refrigerating and Air-Conditioning Engineers climate zones (3B, 3C, 4A and 4C). For climate zone 3, ECC analyses indicated that modular slightly exceeded site-built construction. For zone 4, site-built construction slightly exceeded modular. Nearly all buildings met or exceeded the prescriptive energy code requirements for each climate zone regardless of whether a performance or trade-off compliance path was utilized. Field observations suggest that envelope construction quality in modular buildings could be higher. Results provide insights for researchers exploring energy use in buildings, as well as the basis for a nuanced understanding of normalized operational energy consumption in an ongoing longitudinal study of the same 55 multifamily buildings.