Retrofitting houses with insulation: a cost–benefit analysis of a randomised community trial

Background: Housing is an important environmental influence on population health, and there is growing evidence of health effects from indoor environment characteristics such as low indoor temperatures. However, there is relatively little research, and thus little firm guidance, on the cost-effectiveness of public policies to retrospectively improve the standards of houses. The purpose of this study was to value the health, energy and environmental benefits of retrofitting insulation, through assessing a number of forms of possible benefit: a reduced number of visits to GPs, hospitalisations, days off school, days off work, energy savings and CO2 savings. Methods: All these metrics are used in a cluster randomised trial—the “Housing, Insulation and Health Study”—of retrofitting insulation in 1350 houses, in which at least one person had symptoms of respiratory disease, in predominantly low-income communities in New Zealand. Results: Valuing the health gains, and energy and CO2 emissions savings, suggests that total benefits in “present value” (discounted) terms are one and a half to two times the magnitude of the cost of retrofitting insulation. Conclusion: This study points to the need to consider as wide a range of benefits as possible, including health and environmental benefits, when assessing the value for money of an intervention to improve housing quality. From an environmental, energy and health perspective, the value for money of improving housing quality by retrofitting insulation is compelling.