Abstract Thermal and ventilation performance is studied in composite walls of traditional wood frame single houses. Equations for heat transfer by conduction, natural convection and radiation are solved using analytical–numerical method. For a standard composite wall, parameters controlling thermal and ventilation performance of composite walls, i.e. the channel width and its surface emissivities are varied and their effect on the overall performance is evaluated. It is found that both the channel width and the emissivity of its surfaces play important roles. There is no optimum width to minimize the heat transfer or to maximize the humidity transport. Compared to standard practice, increased width and employing low emissivity films on channel surfaces may improve thermal performance and humidity evacuation capacity of composite walls.