In Korean apartment buildings, internal insulation system is usually applied, so the layer of insulation is disconnected due to structural component at wall-slab and wall-wall joints in envelope. In particular, the amount of heat loss is significant at the wall-slab joints adjacent to hot water heating pipes. In Europe, EPBD(Energy Performance of Buildings Directive) came into effect, and national building energy performance evaluation tool is needed for issuing EPC(Energy Performance Certificate). Though thermal bridges are not explicitly mentioned in EPBD, they are included in the calculation of building energy performance. Linear thermal transmittance is required for energy performance calculation including the effect of these thermal bridges and it should be calculated by an expert with an experience of 2-D heat transfer simulation. If a non-expert can get a linear thermal transmittance without complex calculation, it would be very helpful. So, in this way, in most of European nations, simplified assessment methods for thermal bridges are provided in the national building energy performance evaluation standard. In this study, the regression models which predict linear thermal transmittances for three types of wall-slab joints (internal insulation, internal insulation with subsidiary insulation under slab, and external insulation) are suggested. 2-D heat transfer simulations were performed to calculate linear thermal transmittances for several variables, and then regression equations were derived, which showed a good match with 2-D heat transfer simulation results with p values <0.0001. These regression models can be used for the building energy performance calculation including the effects of thermal bridges.