Interventions that could mitigate the adverse effects of household overcrowding on wellbeing: A rapid realist review with stakeholder participation from urban contexts in England

• Updates a 2013 review on housing interventions, with stronger focus on overcrowding • Includes both peer-reviewed and grey literature with resident and staff involvement • Gives a broader overview to alleviate negative impacts if rehousing is not feasible • While rehousing often reduced overcrowding, it did not always improve wellbeing • Identifies 3 types of interventions: rehousing, home improvements, multisectoral Household overcrowding has increased in England. However, there is limited synthesis of evidence about what can be done to reduce the impact of overcrowding on health/wellbeing. A rapid realist review of English language peer-reviewed and grey literature of interventions from comparable settings to urban contexts in England that addressed household overcrowding/health outcomes. A search was conducted (01.06.23 and updated on 07.03.25) in MEDLINE, EMBASE, Web of Science, SCOPUS and of relevant grey literature sources. Two expert panels informed the review. The first comprised individuals with lived experience of overcrowding in London; the second local and regional government representatives from London, Salford and Doncaster (England). Both panels contributed to guide the scope/literature identification and test/refine programme theories. Final full-text screening and quality appraisal were completed by two independent researchers. Thirty peer-reviewed papers and 27 documents from participating local authorities were included. The peer-reviewed literature, from multiple countries and of variable study designs and quality, contained 14 evaluated interventions across three categories: Rehousing (n=6); Home improvements (n=6); Multisectoral collaboration (n=2). A synthesis of the peer-reviewed literature with expert panel comments and grey literature, identified contexts and mechanisms that could facilitate or hinder achievement of positive wellbeing outcomes. There was reluctance to be rehoused elsewhere and home improvements may alleviate the worst impacts of overcrowding, while residents may benefit from better healthcare co-ordination. Other interventions such as home improvements and improved healthcare co-ordination/access could address wellbeing when residents in overcrowded accommodation cannot or do not wish to move.