Activities in the building industry in Germany concentrate increasingly on a combination of renovation and new-build. A look at current computer aided applications reveals a serious lack of IT support for the whole architectural design process in and within existing buildings (e.g. building surveying, designing on site and the preparation of information for further use in later planning stages). An ongoing interdisciplinary research project undertaken jointly by the faculty of media and the faculty of architecture is investigating methods and techniques for the computer-aided support of the design process in and within existing buildings. The goal is to develop a hardware and software concept for a “design-toolbox” based on SAR (spatial augmented reality) and to implement aspects of this as prototypes. This paper describes the goals of the “Spatial Augmented Reality for Architecture” project and discusses possible fields of application for SAR for supporting the design process in existing buildings from a useris perspective. This paper presents the initial results of the project, the development of a cave-like hardware and software concept called “low-cost projection in room corners” and the description of the core concept based on a client-server architecture. The project is funded by the “German Research Foundation (DFG)”.