This presentation focuses on the environmental implications of two case study projects involving extensive renovation and rehabilitation of older Canadian buildings to serve new functions. Both of the case study projects were submitted as Canadian entries to the Green Building Challenge. One deals with an old locomotive manufacturing and repair facility in Montreal that has been converted to a high tech office building. The other study deals with redevelopment of an entire city block in Winnipeg, with retention of one major building and the facades of several others. The Athena Institute assessed the environmental implications of both of these projects using its Environmental Impact Estimator software, the only North American software for life cycle assessment of whole buildings and building assemblies. The software allows a full life cycle assessment of the environmental effects of different design options and material mixes, and will also take account of operating energy use, including pre-combustion effects, if results are available from a separate energy simulation tool.