The Gallieni high school buildings comprise thermal buffers creating interstitial spacing between outdoors (noise annoyance due to the nearby Toulouse-Blagnac airport) and the classrooms. These interclimatic zones have the thickness of double-skin walls.The idea is to control the evacuation of the solar heat gain during the summer months in what is called the hot layer situated between the underface of the window and the permanent window coverings. Before however, it was necessary to determine a set of calculations where the sun flow at noon on the summer solstice (21st June) would be blocked out but allowing the sun flow to pass at the winter solstice. The results obtained in one small area would be valid on a global level. This phenomenon is a typical example of thermal draft and examples of this phenomenon on a larger scale will be dealt with later. To guarantee the accuracy of all the approaches that we undertook, we set up a very complex modelisation of the area using the soft tool Flovent incorporating in particular a calculation of the effects of direct sunlight.