Purpose: It is intended to improve energy performance and thermal comfort by remodeling old apartments of installing external louvers. And it is intended to present design guideline of louvers for each apartment’s height. Method: Select one apartment in Seoul. One of the most vulnerable apartments is selected by reflecting the climate of Seoul. Using Ladybug, algorithms for each performance element of vertical and horizontal louvers were planned. Through this, the cooling energy demand calculation and PMV were evaluated using EnergyPlus simulation. Result: As a result of the simulation, it was found that the horizontal shade was superior to the vertical shade in terms of energy performance and thermal comfort. In addition, as a result of analyzing by building height, it was found to be more effective in the case of high-rise areas.