While building in different climate zones there are often difficulties in assessing the energetic and room climatic consequences of adjusting key factors of the facade like the percentage of glazing, the amount of sun shading, or the degree of insulation. The FacadeTool was developed to show the interactions between the climate of a location and the facade in terms of room climate and required energy. It provides the user with help in assessing planning decisions at a very early planning stage. At this stage, it is not necessary to quantify specific figures down to the very last detail. What decision-makers need, however, is a choice of variants on which to build and optimize their concepts, forming the basis for ongoing planning decisions. The facade plays a key role in this early phase of planning, since the percentage of glazing, the type of solar protection and the choice of materials have significant influence on the room climate.