The IIS(Internal Insulation System) is typically 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 transfer increases. In particular, the amount of heat loss is significant at the wall-slab joints adjacent to hot water heating pipes. It is expected that the EIFS(External Insulation and Finish System) is the solution to this problem. In this study, annual heating and cooling energy demands of apartment buildings with IIS and EIFS were compared using PHPP 2007(Passive House Planning Package) program adopting the monthly calculation method of ISO 13790 as a calculation algorithm. Heat transfer through thermal bridge was modelled using the linear thermal transmittance. Heat capacity difference caused by the difference of insulation location was modelled using the effective heat capacity considering the effective thickness of materials in direct thermal contact with the internal air. As results, the EIFS could improve the linear thermal transmittances of thermal bridges by 65.1~86.4%, compared to the IIS. Apartment building with EIFS showed 10.2% and 1.3% less annual heating and cooling energy demand, respectively.