LEED (Leadership in Energy and Environmental Design) is a rating system that rates green buildings; LCA (Life Cycle Assessment) is a tool to evaluate the environmental impacts of building materials. The aim of this paper is to demonstrate the importance of integrating LCA into LEED to enhance its rating system. The LEED Gold building presented in this research is the Centennial College Progress Campus located in Toronto, Canada. Using ATHENA (R) Impact Estimator version 4.5 to conduct the LCA, this study analyses how different building envelope solutions and building materials affect the results of the environmental assessment of a whole building over the building's life cycle of 60, 80 and 120 years. Environmental impact assessment of LEED buildings is discussed, further research topics are suggested; for example how to develop specific LCA software tools and integrate them into LCA analysis for green building rating system. (C) 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license.