In the last few years, there has been an increasing number of projects on different scales made with reused or recycled materials. These can vary from building materials or construction elements to furniture, urban equipment, or large structures. The most striking are those signed by well-known architects or internationally renowned architecture and design studios. However, there are interesting examples of circular economy applied to construction that the inhabitants develop in an autonomous, organic, and spontaneous way. This way of building can be found in several informal settlements, where emergency conditions lead people to self-build their homes with the few materials and resources available. Generally, in informal self-built housing, the materials used are construction and demolition waste and everyday items that are in the last phase of their life cycle. While there is no doubt that the misuse of such materials can diminish the quality and comfort of housing, the reuse is a practice that can be improved through the relationship between the community and the professionals of the building environment. This article aims to illustrate how a virtuous circular economy could be implemented in informal contexts by combining the knowledge and skills of the inhabitants with the expertise of the professional architect.