Cost-Effectiveness Evaluation of Energy-Efficient Retrofit Strategies for Pre-1930s Mid-Terrace Houses in the UK ^†

Buildings are a major contributor to greenhouse gas emissions, with a large portion coming from energy use in housing. In the United Kingdom (UK), most of the housing stock was built before the introduction of building regulations that address energy efficiency and, therefore, needs to be retrofitted if net-zero emission targets are to be met. In this paper, the authors present a study of energy-efficient retrofit measures applied to a typical pre-1930s mid-terrace house, based on a home located in Nottingham, UK. Initially, a series of building envelope improvements aimed at reducing the heating demand were evaluated using dynamic building simulations. Subsequently, low-carbon heating systems were introduced, and their impact was assessed in line with the fabric improvements. Then, the annual energy costs of heating were calculated to understand the financial impact of the retrofit strategies and their cost-effectiveness. Lastly, this study also discussed the overall costs of the retrofit interventions, informed by 224 real cases, in terms of their carbon and energy impact. The findings from the simulations suggested a potential 50% reduction in the heating demand through typical fabric optimisation measures. The adoption of low-carbon heating systems resulted in a 50% reduction in carbon emissions compared to those produced by a typical gas boiler. Furthermore, following the adoption of various fabric optimisation measures, the annual running energy costs of heating decreased by 42% compared to their use in non-retrofit scenarios, highlighting the suitability of low-carbon heating such as heat pumps for installation in well-insulated homes with lower heat output demands. The results stressed the importance of coordinating fabric optimisation with the installation of low-carbon heating to maximise carbon savings and suggested that heat pumps can effectively reduce annual energy expenses and lower carbon footprints. The findings also provided an overview of the overall retrofit costs, which are usually overlooked in the literature.