This paper addresses the challenges and conditions of a sustainability transition of suburban areas in Wallonia (Belgium), articulated around energy efficiency in the building and in the transportation sectors. Three scenarios focused on the evolution of the existing building stock are modelled and assessed (the insulation of buildings, an increase in the built density and demolition / reconstruction). Our main findings show that, beyond the traditional polarization of the debates on energy efficiency of our built environment between the “compact city” and the “sprawled city”, a new pragmatic paradigm, focused on the transition of suburban areas by “densification”, can make suburban areas evolve towards more sustainability. However, these main results focused on energy efficiency need to be studied in a larger framework to concretely operationalize a suburban sustainability transition. In this perspective, concrete prospects for a further research project on “suburban densification” are proposed. There address the opportunities for transnational cooperation as well as the proposition of potential research activities. ; SOlutions for Low Energy Neighbourhoods