In this chapter, we make the case for ‘humanizing’ new-build urban mega-projects such as eco-cities by focusing on urban social sustainability, and on the experiences of new residents in newly-built cities such as Tianjin eco-city. We base our conceptual framework in the context of debates over social sustainability (Dempsey et al. 2011; Vallance et al. 2011; Woodcraft 2015), and argue that there is a need to also focus on the way(s) in which socially sustainable urban environments are constructed, in new urban spaces, through relational networks comprised by interactions between residents, buildings, facilities and specifc (e.g. domestic) spaces. In focusing on the spaces of urban social sustainability we draw on Jane Jacobs’ seminal work on, and critique of, the modern city (Jacobs 1961). Jacobs’ work is useful here because of its focus on moving past the plans, blueprints and rational urban visions proposed by master planners, engineers and architects, and towards valuing the role of the rather messier relationality found in the everyday city. [...