Thermal bridges are weak areas of the building envelope in which they can significantly increase the energy load of houses. In this study, we tackle the thermal bridges resulting from windows offset from exterior walls. First, we present an innovative insulating coating which can be used to limit thermal bridge effects. Second, we compute the cooling/heating load coming from the windows offset thermal bridges of a typical French house before and after adding the insulating coating. Third, we compare the time lag and decrement factor when the 2D heat transfer effects of the thermal bridge are taken into consideration. The methodology is to incorporate 2D heat transfer into a whole building energy simulation program. This is done through co-simulation between a 2D heat transfer model developed in MATLAB and the building energy simulation software EnergyPlus using the software BCVTB. This latter enables us to link the two programs and allow them to exchange data at each simulation time step. Results showed that the windows offset thermal bridges energy load percentage of the total house load constitutes around 2-8% depending whether exterior walls have interior insulation or not. Applying 1 cm and 2 cm of the coating on these thermal bridges reduces the windows offset energy load by about 24-50%. Concerning time lag and decrement factor, we obtain high values for decrement factor and low values for the time lag for wall positions near the thermal bridge. Applying the coating decreases, significantly, the decrement factor and increases the time lag.