Rehabilitating vacant buildings offers a strategic opportunity for addressing the housing deficit through socially inclusive and spatially integrated solutions. This study explores the application of Christopher Alexander’s “pattern language” as a design framework to assess architectural quality in the rehabilitation of buildings for social housing (SH). First, the study identifies design patterns in ten rehabilitated buildings in dense urban areas of Porto, Portugal, and examines each pattern’s contributions. Second, it classifies, based on a literature review, the main recurring shortcomings, stemming from suboptimal practices and policies disconnected from functionality, commonly observed in Brazilian SH production – referred to here as “anti-patterns”. Third, it conducts a comparative analysis between the anti-patterns and the design patterns observed in the empirical cases. Results reveal that while the rehabilitated buildings exhibit a clear reduction in most anti-patterns – particularly those related to urban isolation and monofunctionality – the lack of flexibility and absence of resident participation remain a persistent limitation. Findings suggest that Alexander’s patterns provide potentially valuable conceptual and practical tools for addressing design deficiencies in SH rehabilitation. This approach can support the development of evidence-based policies and adaptive architectural practices by identifying design patterns capable of countering structural shortcomings in housing provision.