6. Quantifying Environmental Impacts of Structural Material Choices Using Life Cycle Assessment: A Case Study

The significance of environmental impact quantification for various structural materials is increasingly important for structural engineers to both understand and communicate to others. Building owners and architects are beginning to request this data in the form of a life cycle analysis (LCA), so that the environmental impacts of structural materials from harvesting to processing and beyond can be reported as accurately as possible to an audience interested in more environmentally responsible buildings. Recently, there has also been added motivation in the United States to follow a trend in Canada and Europe to construct more structures out of mass timber products, such as cross-laminated timber (CLT) or nail-laminated timber (NLT). Companies market these mass timber products as viable, sustainable options to compete with conventional steel and concrete construction. Mass timber buildings are commonly perceived as more environmentally responsible than buildings with concrete and steel framing, but very few have attempted to accurately quantify the environmental impacts of this claim or to prove if the hype is indeed correct.

This paper reports the findings of a case study investigation on the above, a seven-story, 85-foot tall new construction office building. The case study focuses on comparing the “reported industry average” structural embodied carbon impacts between four different framing system combinations that include mass timber, steel, and concrete, using the GaBi database within the LCA software “Tally.” The limitations of this study are discussed including differences between the LCA data sets used for each material. The goal of this paper is to develop a comparison utilizing current LCA tools readily available, to highlight the variabilities within that comparison, to assess if an accurate comparison can indeed be made, and to make observations on what are the most critical variables in structural embodied carbon impacts for this building. The ultimate objective is to help advance the reliability of future LCA studies.