Nowadays, the built environment of the Netherlands is making the transition from the linear to circular economy to meet the goals set by the European Union and the Dutch government of 50% circular economy by 2030. However, there is limited knowledge in the built environment for circular economy projects. In order to generate knowledge on the topic, organisations partner up to complete a project. One of the most important aspects of such partnerships between a variety of partners is collaboration. Successful collaboration between partners is crucial for the partnerships to succeed. However, the built environment is a highly fragmented sector which inhibits collaboration. Furthermore, it is unclear how the long term collaboration process would look like in the context of the circular retrofits. The REHAB project is such a case of partnership between organisations, which develops two circular components for housing retrofits, the circular skin and circular extension. This research develops three process maps to understand if it is possible to create a feasible and useful long-term collaboration process for the development and implementation of the circular extension product.
In order to identify the existing knowledge gap in the academia, a literature review was conducted by analysing circular economy projects, circular economy products and by identifying differences between the practices. Comparing the findings, the gap was identified on the end part of the project lifecycle.
To fit the innovative characteristic of the research, the “Research through Design” (Rtd) methodology is chosen, where possible future scenarios in the form of design variants are simulated. During the first step of RtD (analysis), the design parameters and requirements were identified, as well as the main key factors of collaboration in the context of circularity. This identification happened through a literature review and informal interviews with partners of the circular extension. This determined the parameters of the design variants and the requirements that the design variants have to fulfil. During the next step (synthesis), the three variants were identified and the long term collaboration process variants were designed. Based on this information, three design variants were developed (traditional, balanced, innovative). The third step (simulation) involved presenting the design variants to partners of the circular extension in a semi-structured interview format. The answers of the interviews were analysed in order to derive learnings, where the goal was to evaluate the feasibility and usability of the long-term collaboration process design variants. During the last step (validation) the researcher employed the help of former fellow students that have conducted similar researches using RtD to guarantee the scientific validity of the research.
The analysis of the answers collected during the interviews showed clearly that the balanced design variant is the most feasible collaboration process currently and the innovative as the most promising variant for the future. The traditional design variant was deemed not feasible. Furthermore, trust and communication are the core characteristics of a long term collaboration. Another conclusion is that the most important design parameter for the long term collaboration process is the business model, since both client and contractor are highly interested in the financial incentives. The most important lesson derived by the answers of the partners suggest that currently it is still too early to establish a clear collaboration process path for the stakeholders that will take place in ten to twenty years. The research provides valuable information to stakeholders of the circular extension on how to improve circularity through establishing successful collaboration and the steps to guide the collaboration. Moreover, the research provides a good base for future researches to be conducted on the topic of long term collaboration strategy. The difference being that a strategy can be more adaptive for future partners than the rigid guides of a process. Furthermore, it is concluded that countries with high regulated housing sector can adapt to circular economy practices and create successful collaboration easier than countries with a free market.

The circular economy transition requires companies to implement innovative supply chains and business models. However, the number of available solutions for the application in the circular built environment is limited. These solutions could be developed through the co-creation between companies aiming for circular transition. However, it is unclear how the co-creation process would look like in the context of the circular build environment. One such case is the REHAB project where stakeholders develop circular building components for housing renovation. Based on the example of one of the components — circular extension — this research develops three process maps of co-creation to help stakeholders organize the co-creation process for the development and implementation of the service loops of the product. This is done by reviewing the academic literature and identifying the requirements and parameters of co-creation for the case for the circular extension, as well as identifying the co-creation designs already available in the literature. Based on this, further process maps were synthesized. The developed process maps consist of six phases: engaging actor, co-conception, co-design, co-production, co-maintenance and co-disposal. Each phase is subdivided into a number of sub-steps for which the best solutions and/or options are mapped. The developed process maps contribute to the circular co-creation literature by showing a clear picture of the co-creation process that practitioners could follow. Additionally, this research evaluates the developed designs with the project stakeholders and derives six lessons learned that could be applicable for circular building components: 1) Cost efficiency is the main aspect influencing implementation of circular building components, 2) Organizing circular co-creation process requires involvement of a human interaction specialist and circular economy consultant, 3) Circularity is largely dependent of the party that initiates the process and becomes the problem owner, 4) Circularity of circular building components in the current reality depends on the formation of secondhand markets, 5) The co-creation process structure is similar for different circular building components, change only network composition and activities/options that could be considered, 6) Sell and buy-back business model and take-back agreements have the most potential for the circular building components, compared to other solution.

Over the last years, humanity has realised that the current ways of production, distribution and consumption are putting an enormous burden on our planet. One of the most efficient ways to reduce energy consumption is to insulate the entire exterior of the house, including walls and roof, which has proven to be economically viable for areas with cold winters and significant heating requirements, like the Netherlands (Lucero-Álvarez et al., 2016). In the Netherlands, a high number of dwellings require more energy-efficient insulation. In this renovation process, the materials used ought to be chosen wisely, not to cause harm to the environment. TU Delft, alongside AMS Institute, Ymere and Dura Vermeer is working on creating a Circular Skin for the energy retrofitting of Dutch houses. After several tests, the TU Delft Circular Skin proved that technically it is possible to integrate the circularity into facade renovation skin. Circular Skin enhances circular solutions like recycling, repair, refurbishment or reusing the components of the product that will determine a decrease of the raw materials consumption and energy expenditure. (EMF, 2015) Even though the technical design of the Circular Skin was proved to be circular, its integration in a circular supply chain is still uncertain. This study aims to determine the possibilities and limitations of stakeholders in implementing the Circular Skin created by TU Delft in the circular supply chains, constituting the main question. This report will propose new models of circular supply chain and analyse the feasibility of the circular supply chains in the housing renovation sector. Alongside the economic concerns about the transition to circularity, the research will discuss resource efficiency and the environmental impact of every measure.