In Brazil, favelas have consolidated as one of the main forms of settlement for the poor population, with the most recent national census identifying more than 12,000 territories. The formation of and public intervention in these settlements is shaped by two established traditions in housing theory and planning: self-construction, through which residents build their homes incrementally and autonomously, and favela upgrading, through which the state intervenes to improve housing conditions. Yet despite decades of investment by residents and public authorities, high levels of housing precarity persist, particularly inside dwellings. Available institutional indicators capture only general dimensions of this precarity, failing to reach the internal physical conditions of self-built homes, including construction deficiencies, building pathologies, and habitability deficits, constraining academic reflection and policy formulation. In this context, this article draws on a 2025 research project combining CAPI (computer-assisted personal interviewing) household surveys and architectural surveys in Heliópolis, São Paulo's largest favela, to illuminate the problems of persistent precarity and assess the limits of these traditions as responses to adequate housing. The findings contribute to debates on habitability and housing precarity in the Global South, where these traditions are widely adopted and shape the circulation of ideas in similar contexts.