This paper investigates the sensitivity of green roof models’ results to varying simulation input values. The study is carried out utilizing a green roof model that has been validated using experimental data generated at the BCIT Building Science Centre of Excellence. Simulation results reveal that in the mild climate of Vancouver, green roofs contribute to moderate energy savings in the summer and winter seasons due to their added thermal mass and insulation properties, respectively. In retrofit scenarios, a green roof significantly enhances the energy performance of an uninsulated roof compared to a well-insulated roof. Soil thickness is a critical factor; thicker soil layers demonstrate greater solar energy storage, leading to reduced heat loss and rainwater retention capabilities. Additionally, the study finds that green roofs can retain up to 60% of rainwater, aiding in urban drainage management.