Urban voids, these (un)built in-betweens, are often considered from a redevelopment perspective in the habitus of urban planners, without benefiting from any qualities. By taking an interest in the life of these spatiotemporal interstices, we have moved away from stigma to focus on their intrinsic values and, more specifically, on the opportunities they offer to urban environments, over and above their densification function. We then developed the benefits of temporarily activating these spaces/times, as a resource for community, environmental and social use... In fine, we looked at the development of systemic management of urban voids in the Commune of Monthey (VS). The idea is to integrate the temporary activation of urban voids, through a watch period, as a complementary stage to the long cycles of traditional urban planning. The results of this analysis will have shown that certain constraints limit this urban planning process for the public authority. Consequently, in an attempt to overcome these limitations, a decision-support tool in the form of a cartographic matrix was developed and used to project the activation of three urban voids.