The increasing energy consumption of residential buildings in Egypt which reached about 42% of total energy consumption in latest energy statistics, affirms the need for energy conscious design of buildings. Many researches aim at guiding new buildings design to be energy-efficient, however, retrofitting existing buildings can result in significant reductions in energy consumption. This paper outlined different window glass types led to a reduction in cooling loads via the building envelope for the existing building. This paper aims to evaluate the effect of changing windows glass types to reduce energy consumption in the hot arid climate of greater Cairo. The energy analysis carried out by employing advanced simulation via DesignBuilder software for a residential building located in Cairo; this case study analyzed the performance of seven different window glass types in a residential building façade in the different cardinal orientations. The model was validated by taking a field measurement to measure and quantify the temperature of a selected room taken within three consecutive days in May and June 2019 and compared to the simulation tool results, the average error percentage was 2.15%. The results of the simulation showed that changing glass type can reduce energy consumption by up to 18.8%, indicating the significance of energy efficient retrofitting of existing residential buildings.