The next few decades will see a significant increase in high density development in strategic centres in Australian cities, if current city plans are put into practice. The social consequences of this shift towards higher density are profound and will have a significant impact on Australian cities’ social sustainability. An important, yet often overlooked, aspect of this social shift is the different ways in which people interact within and around the buildings in which they live. This paper presents findings from a study of weak tie relationships within and around a high density apartment complex in Sydney. Eighteen residents were interviewed about the weak tie relationships they maintained within 400 metres of their apartment building, and asked to mark where they saw their weak tie contacts on area and building plans. A wide variety of spaces was used by residents to maintain weak ties with others living and working in the area, for a variety of reasons. Weak ties were maintained in spaces where activities were held, that were regularly used through attractiveness (of space or products) or necessity, and/or that catered to particular interests which allowed users to infer other users were similar to themselves. Weak tie relationships are particularly important in a local high density environment because they provide low-level social and practical support while maintaining privacy. The research provides insights into how people use spaces socially in high density, and which kinds of spaces are likely to facilitate the maintenance of weak ties. These findings can inform the design and planning of socially sustainable high density areas.