Detached residential wooden houses are a common type of housing in Japan. Decay of wooden components within the walls is easily caused by condensation or defective flushing. To solve this problem, a double-skin system with a room-side air gap was developed. In this system, during winter, the airflow in the ventilated wall circulates freely around the whole house. Therefore, during daytime, the airflow moves solar heat to base, and releases heat to the house at night which can increase indoor temperature. The purpose of this study is to evaluate the flow rate in the ventilated wall and evaluate indoor temperature increase and reduction of heating load in winter. Therefore, it is important to develop an expression for flow rate in the wall. An airflow-energy simulation program was used to predict flow rates in the ventilated wall, and the performance of air-flows in several exterior walls of the house was investigated. The results verify that the flow rate in the ventilated walls increase with solar radiation. By using the double-skin system with a room-side air gap, the heating load in winter was reduced by 5%.