In planning a building retrofit, energy conservation, thermal comfort and economic benefits should be considered. In this study, retrofit effects of exterior insulating method on preventing condensation, saving energy were analyzed through the heat transfer simulation, energy simulation in the apartment house retrofitted by exterior insulating method cheaper than other retrofit methods. The results of this study show that the retrofit using exterior insulating method can prevent the condensation at the corner walls and save about 20% of annual heating load. The LCC analysis revealed to be effective to select a dryvit system for a building retrofit.