Lx1, an architects studio, is developping an idea formulated in the seventies by Fribourg-based architect Jean Pythoud as urban overpopulation became a concern. In 2006, the questions are still relevant. How can our heritage evolve with historical accuracy ? What strategy to propose in order to repopulate Fribourg’s old city, to revitalize it and to avoid a mass exodus to the suburbs? The plan shows parasitical interventions atop the Auge district’s mysterious roofs. These interventions sprout as vertical emergences in the public sector. They highlight unredeemed spaces, boast new traffic on unused expanses, reveal new perspectives and take advantage of urban accidents to incorporate community activities. The public space flows in forgotten courtyards, generating ermergences, junctures and roof clearings in a positive contamination logic.