Transitional spaces as a domain for public-private engagement in urban regeneration

Transitional spaces contribute to defining urban quality under various aspects: they structure the urban fabric and act as elements of mediation between different categories of spaces: public/private, open/closed, and walkable/non-walkable. The paper addresses the influence of transitional spaces on living habits and their potential role in those processes of urban regeneration that aim at activating innovative forms of public-private engagement. This is basically not just a liminal topic, regarding the aforementioned thresholds between public and private domains, but also a cross-scalar matter, linking the building scale - including typological, technological and distributive modification, functional hybridization, energy efficiency etc - and the urban scale, including appurtenances, public spaces, common services, infrastructures, accessibility etc… An immediately evident theme is the need to recognise and name these spaces. The large plurality of definitions - collective spaces, condominium appurtenances, outdoor spaces, semi-public or semi-private spaces, green spaces, and local public spaces - contribute to keeping these spaces indefinite and not easing the definition of their statute, nor for planning, nor for designing. A thesis of the paper is that transitional spaces offer a rich mix of opportunities for experimenting with innovative solutions, both in terms of typological modifications, and in terms of technological updates. In this framework "green" and "blue" technologies (i.e. nature-based solutions and water-management systems) represent a particularly important field of experimentation. The paper considers quantitative measures of the benefit that nature provides to the community and society, and advances assessments of the benefits of the solutions. The paper concludes with on-field experimentation in a case study: the urban regeneration of a historic social housing district: The "Cogne" neighbourhood in Aosta (Italy).