Hong Kong is a typical global city with growing levels of substandard housing and a reduction in basic living quality. The government implemented a policy of transitional social housing (TSH) in 2018 to enhance the livelihood of low-income families. Nam Cheong 220 (NC220) is the first structural steel TSH project in Hong Kong. This study aims to evaluate the social impact and effectiveness of the project, and quantitative data were collected from individuals in three stages between 2020 and 2022. The first stage (T0) involved interviewing 106 successful applicants of NC220, followed by 91 participants in the second stage (T1) and 88 in the third stage (T2). Longitudinal analysis was implemented to scrutinize the changes observed over time, namely that the living area per capita substantially increased and housing expenses per capita decreased significantly due to residents’ relocation to NC220. Housing conditions and community problems also showed significant improvement. Living satisfaction, neighbour and family relationships also demonstrated positive changes. The most difficult issue for residents was finding suitable housing after staying at NC220. The findings reveal that the first TSH in Hong Kong as an intervention significantly improved the housing circumstances of residents. The social dimensions of housing for enhancing residents’ well-being is worth additional attention.