Uncovering key components of semi-public spaces in multi-unit residences for enhancing social sustainability

• Six indicators were identified as crucial for social sustainability in urban housing. • Security emerged as the most critical factor for resident well-being and interaction. • Socio-economic inclusiveness mitigates inequalities and fosters community cohesion. • SAS and FCM showed risks of instability if key indicators are neglected. • Scenario modeling highlights livability threats from ignoring critical design factors. Semi-public spaces in residential complexes act as intangible bridges between private areas and public urban spaces, playing a vital role in the overall social sustainability of neighborhoods. While the importance of public and private spaces in fostering social interaction and cohesion has been widely studied, the role of semi-public spaces in enhancing social sustainability from different aspects has not received the same attention. This study seeks to identify key indicators of semi-public spaces that contribute to the social sustainability of multi-unit residential complexes, using the Story and Simulation (SAS) approach. Fuzzy-logic Cognitive Mapping (FCM) software was used to model relationships between variables, drawing on input from both experts and residents. The findings indicate that key indicators—such as security, accessibility, socioeconomic inclusivity, distribution of green spaces, sense of belonging, and perception of privacy in semi-public spaces—are crucial for enhancing social sustainability. Based on the significance of these indicators, a framework for the future development of multi-unit residential projects was designed. As case studies, three residential complexes with different typologies were selected to test and validate the extracted indicators. Data analysis revealed significant variations in these indicators across the selected complexes, attributable to differences in infrastructure, facilities, management, planning policies, and residents' social engagement. Additionally, the design, typology, and morphology of these complexes played a key role in influencing the social sustainability of their semi-public spaces. This research presents a scenario highlighting the current unsustainable outlook for semi-public spaces, which, if left unaddressed, could undermine the livability of residents in critical situations.