Sustainable building practices can considerably reduce building's environmental impact in energy consumption. Covering a building envelope with green vegetation, such as green roof and green wall, is considered a sustainable construction practice, as green vegetation has a positive performance in energy savings. It reduces heat flux and solar reflectivity, generates evaporative cooling, increases thermal performance of the building envelope, and blocks the wind effect on the building. This paper analyses the energy performance of green vegetation in a high occupancy LEED Gold standard building in Canada. DesignBuilder software was used to model the energy consumption for heating and cooling, and EnergyPlus software was used to perform the detailed energy simulations. The developed simulation model was validated with the actual energy consumptions of the selected building. Three different scenarios of green vegetation were simulated and the results show that green vegetation could considerably reduce the negative heat transfer through the building façade in summer and winter months. However, the analysis demonstrated that the green vegetation is not cost-effective in winter months or cold climatic regions due to the low energy savings performance. The paper concludes with recommendations to improve the overall energy performance in green buildings.