The KREIS house was planned and built according to the principles of the circular economy. The cycles for materials and resources are largely closed. Where possible, resources are saved and reused. The house consists of a fully developed small living unit with a conservatory built on top. The multifunctional conservatory brings a great additional benefit to the house and is the core piece that enables the overall circulation capability of the building. Thus, this provides additional heat and sound insulation, produces solar electricity, provides additional living space, allows cultivation of plants as in a greenhouse, as well as the reuse of treated wastewater and nutrients from feces. All components were built in such a way that they can be disassembled and reused or recycled at the end of their life. No (hazardous) waste is to be generated. All building materials are free of toxic substances and either of natural origin, durable and recyclable, reused or already recycled. The KREIS house also demonstrates how reduced living space can be lived comfortably with smart amenities. The KREIS-Haus is a demonstration and research object for circular building and living. Visitors can experience the building techniques used in practice, while data for further research and development can be development can be collected.