Facade Retrofit of Residential Buildings: Multi-objective optimization of a typical residential building in Cairo Medhat Kazem 1 , Sherif Ezzeldin 2 , and Moataz Mahrous 3 1 Department of Architectural Engineering and Environmental Design, College of Engineering and Technology, Arab Academy for Science, Technology and Maritime Transport, Cairo, Egypt, medhatmkazem@gmail.com 2 Department of Architectural Engineering and Environmental Design, College of Engineering and Technology, Arab Academy for Science, Technology and Maritime Transport, Cairo, Egypt, sherif.ezzeldin@aast.edu 3 Urban Development Centre, Cairo, Egypt, moatazmahrous@gmail.com Abstract: The population and the residential sector are continuously expanding especially in highly dense cities such as Cairo, Egypt. Due to high demand for cooling energy in the residential sector in Egypt recently, a great attention was paid to retrofit existing buildings to decrease reliance on air conditioning. The existing housing stock is suffering from poorly insulated buildings envelope and lack of energy conservation measures. This is mainly to minimize the initial cost of the construction process while available sustainable guidance is still not mandatory. However, yet façade retrofit solutions include a wide range of variables for wall insulation and glazing types. This study aims to identify best configurations of the building facade retrofit solutions to minimize energy consumption due to cooling and retrofitting cost. A multi-objective optimization was performed on a representative benchmark for typical residential buildings in Cairo using genetic algorithm in order to test different combinations of retrofit options that best meet study objectives. Simulation results were assessed and calibrated against monthly electricity bills using Design Builder as a graphical user interface for EnergyPlus. Best retrofit combinations were highlighted and tested using life cycle cost assessment, and then effective variables were prioritized based on a sensitivity analysis. Keywords: Façade retrofit, residential buildings, multi-objective optimization, Cairo. Introduction In the last few decades, Cairo witnessed a rapid increase in the rate of investments in the residential sector with response to population growth. The majority of these investments have been dedicated towards constructing residential buildings. Accordingly, residential buildings reached more than 70% of the total building stock in Egypt where 56% of total energy consumed in buildings is due to cooling (El-Darwish, 2017; Aldali, 2016). As well, a recent study showed that a sharp rise was noticed in the use of mechanical cooling, and in the increasing total number of sold A/C units (Ediesy and Cecere, 2017). According to Attia et al. (2012), the use of air-conditioning has raised the annual electricity bill by a range of 44% to 57% in residential buildings in Cairo. Nowadays retrofitting existing buildings became a worldwide approach to overcome the huge amount of energy needed for cooling and heating loads. The existing housing stock in Egypt is suffering from poorly insulated buildings’ envelope which is considered responsible for increasing cooling loads (Albadry et al., 2017). Therefore, existing residential buildings are considered a good opportunity for reducing cooling loads through retrofitting. In Egypt, there were some trials from the governments to apply a code for energy performance in buildings, but no guidelines were provided regarding retrofitting existing buildings (Attia and Herde, 2009).