In Japan, wooden detached residential houses are common; the wood components within a wall may undergo decay because of condensation in the wall or flushing defects, which can be a concern. The temperature distribution throughout the house, such as a high temperature in the attic space, can cause discomfort to the occupants. A double-skin system of room-side air gaps is considered to be an effective technique to handle these problems. In this system, during the summer, the airflow driven by natural ventilation moves through the room-side air gap in the wall and removes heat load from the inner surface of the insulation material or from the surface adjacent to the rooms inside. Although this system has been applied to many houses, further study on the design specifications for parts of the ventilation route is still required. In this study, airflow network simulation was carried out using TRNFlow to evaluate the performance of this system under different conditions. A standard residential house model was simulated by considering conditions of summer. On the basis of the results, it was verified that the total airflow rate exhausted from the rooftop vent fluctuates with the ambient temperature; the flow rate distribution in different walls was also determined. Sensitivity analysis was performed on each part of the ventilation route with different opening areas; the opening area of the wall was found to have more effect than the rooftop and base vents on the total amount of airflow. When wind is blowing outside, the total flow rate increases. When there is no wind outside and the windows are closed, this system reduces the cooling load of an ordinary detached house by 15.5%.