From underdetermined to overdetermined space: public/private interfaces and activities in residential alleys

The underlying logic of two well-established urban design concepts, active use and active interface, while applicable to streets and activity centres, may have limited bearing on residual urban spaces. As such spaces can be perceived as problematic, they are often replaced with conventional forms rather than valued for their uniqueness. This study examines the relationships between public/private interfaces and activities in residential alleys in Melbourne, Australia. These alleys are undervalued urban features that sum to vast amounts of land in areas deprived of public space. They are reappropriated for social activities and are also used as access for infill developments. The findings show that the conventional infill developments create overdetermined conditions that limit social activities. In contrast, the impermeable and blank interfaces that would be problematic elsewhere enable a wide range of usage. The key quality of these preferred interfaces is underdetermination, where multiple possibilities could emerge and exist simultaneously.