A popular retrofit option is to install an exterior insulation finish system to the walls of existing buildings. This study evaluates the thermal and moisture performance of such a system with a vented wall assembly. In addition to being a case study, this field monitoring was intended to verify computation methods of building envelope performance. The long term monitoring was designed to be non-destructive so that the building envelope performance is not affected by the measurements that are made, and to allow easy removal of sensors for recalibration and retrieval at the end of the test period. The field monitoring is planned for two years to capture a wide range of environmental conditions. This paper discusses the instrumentation used in the study and presents interim results of the thermal resistance of the wall and surface moisture.