By 2030, more than the equivalent of two Earths will be needed to meet human demand for natural resources, with the construction industry responsible for 60% of the world's raw material extraction and 25% of the world's total waste generation. As waste management and waste reduction are not considered in the early design stages, the phase with the greatest impact throughout the life cycle, 50% construction and demolition waste is generated at the end of the building life cycle. In order to reduce raw material extraction and the amount of waste generated, it is of utmost importance to increase recycling rates by reusing materials and building elements, thus enabling a circular economy. A transition to a circular system is essential, especially in the construction industry, as it is responsible for about 38% of all C02 emissions and has a major impact on resource depletion. The European Green Deal developed the classification system of the "EU Taxonomy" based on six environmental objectives, according to which sustainability of investments are evaluated, and EU Taxonomy compliance is assessed.

By creating a digital ecosystem based on the components of circular digital twins, generative design algorithms and virtual reality (VR), this research project aims to support the decisions that enable the circularity of building structures and integrate end-of-life concepts into the design at early design stages. Building on the research project "Wohnen 4.0 - Digitale Plattform für leistbares Wohnen" (Housing 4.0 - Digital Platform for Affordable Housing), the project "CircularTwin" aims to use the knowledge base generated in "Wohnen 4.0", the BIM object libraries and associated material building passports and enrich them with the criteria of the circular economy. The framework for BIM-supported material building passports was already elaborated in the predecessor research project "BIMMaterial". With regard to building information modeling and life cycle changes (adaptability and flexibility), "CircularTwin" envisages the application of BIM-based digital twins, which are generated and evaluated by means of Generative Design in the context of a large number of variants in the early design phase and the re-use phase. In addition to the Generative Design methods, which enable an automated and variant generation of Digital Twins coupled to a BIM object database, algorithms are also designed that enable an evaluation of the circularity, Material Building Passports (MGP) and EU taxonomy compliance. By visualizing the end-of-life (EoL) scenarios of the generated digital twins in a VR platform, including user interaction and variant generation, the decision-making process of the stakeholders involved in the design and construction will be supported. The digital "Circular Twin" ecosystem thus enables the early implementation of the goals of the circular economy and sustainability as well as end-to-end digitization in the construction industry.