Jane Jacobs’ The Death and Life of Great American Cities, remains revered as one of the most seminal and enduring statements about urban social sustainability (Jacobs,1961). Despite subsequent advances, collectively laying foundations for socially responsive approaches to urbanism, recent discourse highlights that the essence of Jacobs’ sociological aspirations remain far from sufficiently embedded in the mainstream of theory and practice (Cuthbert,2007; Punter,2010). Fifty years on, there is still no fully coherent and effective approach capable of delivering the kind of urban realm advocated by Jacobs.

In response this paper outlines the development of a conceptual framework for urban spatial structure, building from John Habraken’s discussion about the structure of the ordinary built environment (Habraken,1998). This provides a platform from which to construct an anatomy for transitional edges, here defined as urban socio-spatial domains where human habitation and material form interact. Transitional edges provide an important conceptual thread capable of reconnecting social and spatial dimensions of urban form and thereby have potential to contribute to planning and design decision making for urban sustainable living.

Active edges, in particular, have broad recognition for their relevance to the encouragement of social life in urban realms throughout the development of urban design theory (Lynch,1960; Cullen,1971; Alexander,1979; Bentley,1985; Frank and Stevens,2007; Gehl,2010). Nevertheless, the practical application of this remains hindered by a paucity of focused design guidance that can draw together urban spatial organisation with the way social processes become activated. The transitional edge concept addresses this limitation by providing a theoretical and practical framework in which the built form, open space and social dimensions of urban settings can be brought together as an integrated system (Thwaites, Mathers and Simkins,2013). In building this conceptual framework we see particular relevance for application in the kind of mixed-use, compact urban development increasingly associated with the delivery of urban social sustainability (Rudlin and Falk,1999; Urban Task Force,1999; Gehl,2010).

We will present an anatomy based on an interconnected segmental system representing different elements of socio-spatial building blocks for the development of transitional edges. This will form the basis for demonstrating the importance of providing edge settings with a wider range of spatial extent than is currently evident in contemporary urban design solutions. The paper will conclude by illustrating examples of the social benefit that can accrue from its application. This will emphasise in particular: the importance of ‘porous’ spatial structures to the delivery of compact, mixed use and socially beneficial urban settings; the significance to human well-being and self-esteem of ‘adaptable’ spatial structures capable of personalisation and change; how spatial structure and material arrangement can give inhabitants better control over the balance of need for ‘privacy and social interaction’; and how ‘soft green margins’ in transitional edges can deliver eco-system services, habitat creation and restorative benefits in urban environments. We will argue that, collectively, these properties of urban environments, delivered through application of the transitional edge framework, can contribute spatial cornerstones of approaches to urban sustainable living by integrating material, spatial, social and ecological considerations.