This project extends the structural and construction-oriented knowledge of architecture on the circular economy with a social anthropological research approach, which deals with the practical knowledge and everyday handling of building materials on demolition sites, in architectural offices, in companies and on the construction site. By investigating the challenges of using different building materials such as steel beams, glass panes, wood or bricks and in collaboration with experts in reuse, the project is looking for successful approaches to advance the circular economy. The comparison of the situation in four European countries with similar conditions in the construction industry enables an exchange on sustainable solutions. The project supports the efforts of the Federal Office for the Environment FOEN, which promotes the reuse of building materials in order to achieve the climate target 2050 and the energy strategy 2050. At the intersection of anthropology and architecture, this project explores the practical challenges of reuse. A new and radical socio-material perspective on reuse is key not only to understanding ecological and economic resistances within the circular economy, but also to finding methods to optimize the reuse process.