Double Skin Façades (DSF) are nowadays very popular with architects and investors. The DSF adaptive behavior may offer interesting opportunities for energy saving and comfort. However the thermophysical behavior of DSF should be evaluated by means of building dynamic simulation, using models taking into account the combined solar gains and heat transfer through DSF. In this paper a model for naturally ventilated DSF, based on the coupling between fluiddynamic and thermal problems, is presented. The fluid-dynamic model considers buoyancy, wind and friction forces and derives the mass flow rate as function of the temperatures. The thermal model derives the air temperature profile along the channel as function of the mass flow rate. In this way the convection inside the channel is modeled by a simplified integral approach adopting average bulk temperature and superficial heat transfer coefficient correlations. A first comparison between the model, the standard EN 13363-2 and experimental data from a test facility is presented and discussed.