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Indoor environmental conditions are increasingly recognised as important determinants of public health. A substantial body of epidemiological research demonstrates that exposure to poor housing conditions, including cold temperatures, damp, mould, and indoor air pollution, are associated with a range of adverse health outcomes. These include respiratory illness, cardiovascular disease, exacerbation of chronic conditions, and poorer mental wellbeing. Given that people in the UK spend approximately 80–90% of their time indoors, the home represents a critical site where environmental exposures are produced and experienced. Despite this, research and policy attention has historically focused more on the effects of outdoor air pollution, often treating the home as a protective space rather than as an important environment in its own right.

At the same time, the UK’s commitment to achieving Net Zero emissions by 2050 has placed significant policy emphasis on housing retrofit. Retrofit programmes involve upgrading existing homes to improve energy efficiency and reduce emissions through measures such as insulation improvements, upgraded heating systems, and mechanical ventilation technologies. These interventions are intended to reduce energy demand while improving thermal comfort and lowering household energy costs. However, socio-technical analyses of housing and energy systems highlight that the outcomes of retrofit cannot be understood solely through technical performance measures alone. For example, studies examining energy efficiency retrofits have shown that certain interventions may increase indoor pollutant concentrations if ventilation systems are poorly designed, maintained, or operated. Similarly, research on domestic heating and ventilation technologies suggests that household controls are often difficult for residents to understand or operate effectively, which may limit the expected environmental and health benefits of retrofit programmes. Further, informal conversations with families participating in Imperial College’s WellHome II study indicate that some households of retrofitted homes have experienced problems with mechanical ventilation system performance and maintenance, while others reported new instances of damp and mould that were not present prior to retrofit.

In addition to this, housing-related environmental risks are unevenly distributed across populations. Research in housing, public health, and environmental justice consistently demonstrates that racialised and socioeconomically disadvantaged households are more likely to live in older, poorly maintained, and energy-inefficient housing, where hazards such as damp, mould, and overcrowding are more prevalent. In this context, retrofit interventions that treat housing conditions as a neutral baseline, without accounting for the structural health, social, and housing factors shaping how retrofits are experienced, risk slowing delivery and reinforcing existing structural inequalities.

Taken together, this evidence demonstrates that housing retrofit cannot be evaluated solely through energy performance metrics but must also be understood in relation to the social and structural conditions in which it is implemented. Addressing how retrofit reshapes indoor environmental conditions and affects occupant health therefore requires sociological research that draws on participants’ own insights into their everyday experiences of living with these changes over time.