In this article, we discuss the role of solidarity in collaborative housing in relation to the trajectory and discourse of the Danish idea of co-operative housing (andelstanken). Our analytical perspective draws on the concept of social mechanisms and a framework suggested by the social scientist Steinar Stjernø. We argue that collaborative housing based on individual (home) ownership of shares and user-rights to apartments are susceptible to the mechanism of “conflicting interests between different categories on the housing market”. Moreover, we suggest that this mechanism has a tendency to further the economic interests of residents, at the expense of the external solidarity with groups looking to access affordable housing. Our argument is supported by theoretical reflection, the historical trajectory of co-operative housing in Scandinavia and empirical analysis of the Danish case.