Transitional brownfields constitute real laboratories for experimenting new uses of urban space. This article describes the role of researchers to co-construct urban space with inhabitants and local actors. We query this process of co-construction by mobilising an approach of user innovation in economics. Von Hippel research (2002, 2006) is employed, as source of new insights on use co-creation and new related good co-production. Researchers are intermediary figures in accompanying inhabitants. They support the redeployment of transitional uses of brownfields towards new objectives of urban renewal, following the example of the scientist intermediary role in Von Hippel’s research (1976). The interest of Von Hippel’s research is that it allows us to understand how to take advantage of user’s creativity to renew needs by offering them design tools. We conceptualize an analytical framework of co-construction of transitional brownfield spaces according to four steps (activation of new uses ; recombination of existing resources to create these new uses ; uses appropriation ; diffusion of these new uses). We test it on a priority district for urban renewal in the city of Angers. Researchers and students from the Vegetal campus have co-constructed with inhabitants modular in situ facilities. The latter combine knowledge and practices from the plant world and follow the aim of reversibility. The inhabitants are involved in a public participation approach whose participation degree varies according to the different process stages of urban-space co-construction. This hybridization has produced new uses as result of new interactions between campus resources and neighbourhood resources: food supply, recreational and social new uses. The researchers and the students involved accompanied inhabitants in this transition. This one responds to an ecological and climatic challenge they will be able to integrate into their future projects and tasks. This article opens new avenues for research about incremental innovation in the urban environment.