Over the past two decades, the Greater London Authority (GLA) has pursued the delivery of high-density development in London in order to respond to population growth whilst protecting the green belt. Though high-density places have been associated with sustainable outcomes, it is well documented that residents interact less frequently and build fewer relationships in these environments. This can be particularly detrimental since social contact is fundamental for our general well-being and happiness. In response to this problematic, this study explored if and how we can design for social interaction in high-density housing. To do so, it adopted the process of inducting theory from case studies. Firstly, three case studies of recently completed developments were undertaken to determine whether social interaction was a driving factor in the design process, the type and location of social interactions, and clarify the influence of physical design on social contact in comparison to other factors. These design-led schemes were chosen for investigation as award-winning developments which had received commendation for creating the foundations for a strong community. Next, a cross-case comparison was undertaken to identify hypothesis that addressed the research question and objectives. Providing support for existing literature in the context of high-density housing, it was discovered that limiting the number of apartments to a building allows for collective stewardship, and that communal areas shared by smaller groups are used more intensively. Moreover, combining shared paths and communal areas was observed to support fleeting interactions and helped to nurture a local sense of community. New findings included that externalising the circulation spaces of multi-storey apartment blocks can facilitate conversations between neighbours, and that bike stores can represent an epicentre for contact if internalised and co-located with shared paths. Notably, the impact of physical design factors was not deterministic.

The public open space is the carrier of social, economic and cultural activities for the residents. In the process of urbanization, the public space is constantly compressed. Social interaction serves as a link between communities and plays an important role in the sustainable development of residents' life and the whole society. However, differences and gaps in space and culture make social interaction less frequent that community members are reluctant to communicate with each other. This had adverse effects on public life and the physical and mental health of individual residents. This research summarizes the importance of social interaction with literature review. It also highlighted the underlying determinants of providing attractive open spaces in mixed communities to encourage interaction. The study of the leisure behaviour of different groups of people also emphasizes the basic understanding of the ideal way of living for all groups and the use of public places. The case study puts forward the possibility of space arrangement of public space, encouraging public participation in design and construction, renovation of existing facilities and promotion of sustainability. This research attempts to combine these findings into a comprehensive study of public open spaces in complex communities. From the key findings, a practical toolkit is proposed. The toolkit includes physical design principles as well as policies to support the provision of spaces that are attractive and able to encourage interaction by promoting participation, shared activities, joint design and overcoming physical barriers. Then, on the application side, a site was chosen from a fast-growing city in a developing country to gain a broader perspective. The toolkit was configured at the site to test and evaluate its usefulness and feasibility. It's also used to spot potential conflicts. The research aims to promote public interaction and encourage people to live more sustainable lives.