The IIS(Internal Insulation System) is applied in most Korean apartment buildings which are the most common type of residential buildings. Consequently, there are many cases in which the layer of insulation is disconnected by the structural components at the wall-slab and wall-wall joints in the envelope. These joints become thermal bridges where the risk of heat loss increases. It is expected that the EIFS(External Insulation and Finish System) is the solution to this problem. In this study, annual heating and cooling loads of apartment buildings with IIS and EIFS were compared using Design Builder program in order to evaluate the thermal storage effect of EIFS where the concrete thermal mass is located inside of the insulation material. As results, the apartment building with EIFS could reduce annual heating and cooling loads by 2.4% and 4.1%, respectively.