The landscape of urban sprawl is expanding unabated. Significant research has focused on new community design, but the legacy of unsustainable sprawl created throughout the past century still poses profound challenges. Scant research has examined how existing suburbs might be retrofitted for sustainability. This study explores whether sustainable design principles can improve ecological health and enhance desirable suburban character in a suburban retrofit scenario. Principles of green urbanism were applied in a design for an existing neighbourhood in Guelph, Ontario, and the results critically assessed using the U.S. Green Building Council's LEED for Neighbourhood Development rating tool. Results indicate that green urbanism principles and the LEED-ND rating system can effectively address ecological health in a suburban retrofit, but outcomes relating to desirable suburban character are not as clear. Outcomes suggest that suburban retrofit designs may require slightly different sustainable strategies than those used for new community development.