Activities in the building industry in Germany concentrate increasingly on a combination of renovation and new building. A prerequisite for computer-aided planning in the context of existing buildings is both the use of on-site computer aided techniques and the integration of all professional disciplines in an integrated information and communication system. How will computers be used on site in the future? Which equipment will be needed? 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 with and within existing buildings. The aim of this project is the development of a practice-oriented toolbox for the architectural design process based on SAR (spatial augmented reality). This paper focuses on Augmented-Reality based user interaction on site using laser pointer tracking. The project is funded by the German Research Foundation.