In many middle- and high-income countries, existing buildings will occupy the majority of building areas by 2050 and measures are needed to upgrade the mentioned buildings for a sustainable transition. This research proposes a method to mitigate the energy consumption of existing educational buildings using four energy efficiency measures (EEMs). The proposed method divides simulations into two main parts: simulations with and without using heating, ventilating, and air conditioning (HVAC) systems. Four passive EEMs are used, including window replacement, proposed shading devices, new insulations, and installing a new partition wall for the entrance part of the building. This research uses a simulation-based method to examine the effect of each EEM on the energy consumption of the building using DesignBuilder software. The steps of data collection and modeling in this research include collecting raw data related to the physical characteristics of the building experimentally and creating a basic model. Afterwards, simulation scenarios were defined based on the proposed method, and several simulations were carried out to examine the impact of each EEM on the energy performance of the building. Two environmental parameters of the simulation process, including indoor air temperature (IAT) and relative humidity (RH), were used. The measures reduced the heating and cooling demands in the building by 80.14% and 15.70%, respectively. Moreover, the results indicated that the total energy consumption of the building were reduced by 10.44% after retrofitting measures.