Sustainable Structural Design Using Life Cycle Assessment Open Access
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In sustainable building design, emphasis continues to be placed on reducing building operating energy use, but as buildings strive to become net-zero, environmental impacts embodied in the production of building materials are gaining more consideration. Life cycle assessment (LCA), a methodology that evaluates the environmental impact associated with all stages of a product's life, has been incorporated into green building codes and rating systems in recent years as a performance-based alternative to more prescriptive material sourcing requirements. The U.S. Green Building Council plans to incorporate LCA requirements into the next version of Leadership in Energy and Environmental Design (LEED), the most widely adopted green building rating system. With the release of the new version of LEED (LEED v4), structural engineers will have to address the needs of clients seeking to achieve LCA credits. Previous studies and case studies presented in this paper demonstrate that structural materials contribute, on average, to 50-60% of the overall embodied environmental impact of a building, indicating that structural engineers are posed to play a significant role in meeting green building code and rating system LCA requirements.LCA has limitations of its own; as demonstrated in this paper, baseline values of embodied environmental impacts cannot be confidently determined for environmental performance comparison purposes. For this reason, green building code and rating system language specifies that environmental impact reduction must be demonstrated with respect to a reference building, which must be of the same size, location, and function as the intended design. To evaluate the applicability of LCA requirements in comparing framing options that are otherwise not designed with the intent of a reduced environmental impact and to determine if changes to structure alone can meet these requirements, four case studies are presented within the context of the draft LEED v4 language. Each case study has multiple framing material options, from which the option with a greater overall environmental impact is chosen to serve as the reference building.One of four case studies met all of the draft LEED v4 LCA requirements; the three remaining case studies failed on the basis of an increase in at least one environmental impact category. This indicates that based on the existing functionality of LCA, structural engineers cannot readily meet the requirements of the draft LEED v4 rating system through comparison of framing material options alone. Aware that current LCA methods are limited, structural engineers may instead need to design with the intent of a reduced environmental impact through material specification or other design practice in order to meet green building code and rating system LCA requirements.