The objective of this project was to provide an overview of Life Cycle Assessment (LCA) and to demonstrate its application as a tool to provide a scientific comparison of alternative construction options for a commercial building in the Canadian context. The work entailed a quantitative assessment of the embodied environmental impacts of typical office buildings using a steel frame, and a concrete frame alternative (and associated components) in Toronto. Through the use of four assessment strategies, this study has indicated that the steel framed building performs better than the concrete building in most impact indicators, excepting primary energy and eutrophication potential. However, additional buildings should be assessed in order to confirm this finding. Furthermore, it was found that the manufacturing phase represents over 90% of the embodied impacts of the whole building. The study also advises caution when comparing different LCA studies and identifies its difficulties.