Impacts of insulation retrofits and electrification on residential energy use across multiple housing types in the historic Japanese city of Kyoto

As Japan commits to achieving carbon neutrality, historic cities like Kyoto face disproportionate challenges in reducing residential energy consumption. These cities are constrained by aging building stock, poor insulation performance, and the need to preserve the historical and cultural value of traditional houses—making the decarbonization of the residential sector especially urgent and complex. This study constructs a high-resolution, multi-scenario bottom-up simulation framework that integrates household demographics, building archetypes, and end-use device compositions to evaluate the energy-saving potential across detached houses, apartments, and traditional wooden houses. This integrated approach enables the tailored design of retrofit strategies for different housing types. Results show that energy load profiles vary significantly by housing type. These load characteristics shape the effectiveness of retrofits: detached houses and traditional houses achieve the greatest reductions, with heating energy use decreasing by 21.3% and 11.7%, respectively, through G3-level and compartmentalized insulation retrofit. Apartments respond better to electrification, as envelope improvement yields limited benefit. High-efficiency air conditioners reduce total per household energy use by 23.3% in detached houses and 27.9% in traditional houses, while heat pump water heaters cut 30.6% in apartments. When optimal insulation and electrification strategies are applied sector-wide, residential per household energy use can be reduced by up to 51.7%. These findings underscore the need for differentiated, integrated approaches to retrofit policy in aging, historically significant urban contexts.