Housing Stock Optimisations

In Japan, aging housing complexes are considered a key component of the national housing stock. However, renovation projects often prioritize initial costs over long-term energy performance. Although retrofitting insulation effectively reduces energy consumption, budget constraints and competing priorities, such as architectural improvements and airtightness measures, limit its adoption. Few academic studies have quantified the economic and energy-saving impacts of retrofitting existing apartment buildings. This study uses TRNSYS simulations to evaluate retrofitting scenarios for a typical aging apartment complex. The analysis focuses on lifecycle costs and annual heating and cooling loads. Results indicate that ceiling insulation yields the largest reduction in heat load. The numerical data generated by this research offer practical guidelines for design practitioners evaluating retrofit options. A cost breakdown based on material and labor estimates is provided to demonstrate the trade-off between investment and energy savings. Sensitivity analyses assess the robustness of the findings when insulation thickness and energy prices vary. This study provides a database of thermal performance metrics for existing buildings to support decision-making in renovation projects. The implications include optimized retrofit strategies that balance initial costs and energy efficiency, thereby promoting the sustainable management of aging housing stock. The results serve as a reference for architects, engineers, and policymakers involved in building energy retrofits. By quantifying the relationship between insulation measures and thermal load, the database helps planners mitigate risks such as indoor thermal discomfort and cold-related health hazards in older residences.