Improving energy efficiency of the building envelope in renovations requires new technologies and materials. Additional exterior insulation system can improve the energy efficiency and indoor thermal comfort. Safe moisture performance of the additional exterior insulation assembly requires suitable properties for the materials. Rigid phenolic foam insulation is a new product that offers several advantages. The thermal conductivity of the material can be 0.020 W/mK (0.0116 BTUIT hr-1 ft-1 oF-1), allowing good thermal resistance with significantly thin layers. Rigid phenolic foam has relatively low water vapor diffusion resistance at high humidity levels where drying efficiency is needed. This paper presents a numerical study about the moisture performance of an exterior renovation systems applied on concrete sandwich walls under cold climates. The renovation structure has exterior sheathing, ventilated cavity and additional thermal insulation. The main moisture loads were caused by the wet exterior layers of the old wall exposed to driving rain before renovation. The study compares the drying efficiency and humidity conditions of the renovation application using rigid phenolic foam or mineral wool insulation. All the renovation cases improved the moisture safety of the structure from the original, and the risk for mould growth remained low for both the insulation materials. The results show that the studied renovation system can be safely applied using rigid phenolic foam insulation.