Policies expanding social housing are central to debates on affordability and spatial inequality. This paper examines how different forms of social housing affect local housing markets and neighborhood composition in the \^Ile-de-France region between 2011 and 2023. Combining geo-referenced transaction data with administrative records on buildings and residents, we compare the local impacts of traditional social projects (HLM), mixed social-private buildings, and conversions of private dwellings into social units. Using building-centered fixed effects and a nearest treatment group estimator, we find that none of the three types generates economically meaningful effects on nearby housing prices. Turning to composition, HLM buildings produce the strongest aggregate shifts, increasing the low-income share and reducing the high-income share. We then isolate spillover effects on the surrounding private housing stock. HLM buildings trigger an inflow of middle- and upper-income households into nearby private dwellings, absorbed through densification, without displacing low-income residents—the decline in the low-income share is driven by dilution, not displacement. For mixed buildings, the inflow is concentrated in the market-rate units within the building itself, and higher-income households do not avoid cohabiting with social tenants. For conversions, low-income households decrease partly due to transition with their reclassified units. These results challenge the view that social housing triggers residential flight or depresses local markets, revealing instead heterogeneous spillover dynamics that depend on the modality of provision.

CY Cergy Paris Université – THEMA Seminar; CEMFI – BUDIE PhD Seminar & Lisbon Urban and Public Economics (LUPE) Mini Workshop on Housing – ISEG

ITO (EU Tax) Seminar – Paris School of Economics; CY Cergy Paris Université – THEMA Seminar & CEMFI – BUDIE PhD Seminar. Upcoming presentations: CaCHE Conference – University of Glasgow (2-3 Sep, 2026), 5th Workshop on Residential Housing Markets: Climate Risks and Affordability – University off Cambridge (7-9 Sep, 2026) & 2nd Early Career & PhD Workshop on SocioEconomic Mobility and Public Policies – WEIPO, Universidad de Alcalá (22-23 Oct, 2026).