2020 is a strange and disruptive year. The pandemic virus COVID-19 controls people’s lives. It influences the way we live, love, and work. Offices are empty while people work from home. When, and if people are going to work in an office again like they were used to, is the question. The events of 2020 are an extra showcase that the way we use offices is subject to change. Therefore, offices should be designed in a way that they are adaptable, reusable, and can respond to changing needs. Circular design can help to make our offices future-proof. However, since the circular economy gained attention in the office building sector, only limited progress has been accomplished. A problem within the office building sector is that insight into the possibilities of circular design is lacking. Moreover, in literature there is no circular design model specific for the building industry. Therefore, this research aims to develop a decision support tool that stimulates the communication between client and designer and provides clarity about the possibilities of circular design. This resulted in three main insights. First, a building consists of different layers with different lifespans that should be able to be refurbished, replaced, and recycled without damaging other layers. Consequently leading to an extended lifespan of the complete building and increased adaptability and reusability. Second, practical circular interventions can be categorized into four themes which are based on circular theory. Those themes are adaptability, reusability, materials, and process. Third, decisions regarding circularity should be taken early in the design process. Especially when the lifespan of the building layer is long. Understanding which possible interventions could be taken in what stage of a design process helps prioritising them and thus creating windows for circularity.