Municipalities often struggle with reconstructions and refurbishing of buildings in public ownership. This is not only because of limited expert capacities that municipalities struggle with (municipal architect position or urban planner position is vacant, or non-existent etc.) or lack of finances. There is an increasing need and demand from municipalities for redefining buildings' original purpose and finding new, sustainable and innovate functions. They have to decide not only how to reconstruct, but how to rethink its original purpose. The case study from a city of Slaný shows how participatory design can serve the goal of finding new functions of a public building and effectively contribute to the planning phase of reconstruction projects. Sustainable urban development should react to people's needs, new technologies and environmental challenges. Reconstruction projects should reflect innovations in both technologies and approaches and respond to newly emerged functions. The methodology demonstrated in the case study can serve as a tool for assessing preferences of citizens, needs of the municipality and bridge the gap between politicians, experts and citizens by supporting efficient communication and evidence-based decision making. Moreover, this case shows how to ensure social sustainability and project effectiveness by involving multidisciplinary teams, in this case architects, urban planners, sociologists, communications experts and environmental and engineering psychologists.