The Circular Economy (CE) in the built environment has gained ever more attention as discussions around the threats of global warming, resource scarcity, environmental impacts, and energy emissions intensify. The building industry accounts for approximately 40% of carbon emissions and reusing vacant buildings – thus slowing resource loops – is one of the strategies on offer to address this. However, research shows that the adaptive reuse of vacant buildings also contributes to their embodied emissions if the process is not fully aligned with CE principles. In addition, the CE is often conceived of as a binary outcome: either projects are fully circular or not circular at all. Identifying how far a project still has to go to become fully circular is an essential step in closing this gap, but how can this be done? This research contains an examination of the processes which are considered to be of importance at the inception of a project. In it, the results of two case studies, exploratory interviews with experts, and a literature review are used to design a decision support framework (DSF) to support decision-makers in housing associations in pursuing greater self-sustainability in their assets. This research also includes an exploration of existing, complementary CE methodologies, and an illustration of how they can be applied to adaptive reuse projects. This involves an examination of the complexity of these CE methodologies, and the delivery of a series of practical steps to achieving a low, medium or high degree of circularity. Using the DSF, an evaluation of a circular project in the Netherlands is then carried out, and recommendations and a step-by-step plan for achieving a completely circular project are set out.