the city and to incorporate existing buildings to a greater extent? Over a period of three years, the 33.3% design studio of the chair of De Vylder created 22 projects that use specific case studies from the city of Zurich to develop an alternative approach to urban transformation. The design studio participants closely examined urban development practices of different actors, from institutional investors and the public sector to cooperatives and private owners. Based on the specific objectives of owners and developers, the students developed strategies for dealing with the existing building stock. Thus, this publication offers insight into a way of working that does not strive for a 100% solution in the design, but rather seeks gradual, fragmentary approaches between new and old. The 33.3% in the title refers to more than just a numbers game ¿ it is an approach to design that revolves around the economy of resources and considers the existing building as a resource to be used ¿ continuing with what is already there instead of complete demolition and replacement. The publication outlines strategies for dealing with single-family residential areas as well as settlement structures in agglomerations and large-scale buildings. In five chapters, the possibilities of partial preservation are outlined using Zurich-related case studies. The potential of this method is visualized in a photo series of realized buildings, while plans, interviews and essays make the design approach accessible for further practical implementation ¿ both in Zurich and beyond.