Rooms with high windows are likely to have comfort problems caused by cold air down draught, which are usually solved by placing heating appliances underneath the windows. In the city of Zug, Switzerland, a highly insulated educational building with a concrete core system for heating and cooling is planned. The purpose of our investigation was to find out whether any measures are necessary in this building to compensate the effects of down draught in the occupied zone. Special attention has been paid to the effect of passive measures Like air how obstacles or openings in the window sill. Experiments were carried out in a room climate laboratory on 1.1 scale to measure the down draught and the thermal comfort in the occupied zone. Several configurations of window sizes, insulating standards and outside temperatures were investigated. In addition, the results were compared to values obtained from analytical calculations and from literature. The conclusion was that the window frame, not the window pane, is the critical element and that there will be no unacceptable draught risk in the occupied zone, as long as the window frame is also highly insulating. Therefore, no additional measures to compensate the down draught were planned for the building in Zug. Furthermore, it was found that the down draught is not only dependent on the window temperature but also on the heat load in the room, i.e, a heat load increases the boundary layer thickness and decreases its peak velocity.