Integrated retrofit strategies for UK housing: simulation-based assessment of insulation and green wall combinations across construction eras

This study evaluates retrofit strategies that combine wall insulation and green wall systems in three typical UK residential buildings from the 1920s, 1970s, and 2010s. While both approaches have been individually explored, their combined thermal and economic impact across housing eras remains underexamined. Using 64 thermal simulation scenarios in DesignBuilder, the research analyzes effects on U-values, energy use intensity, and heating gas demand, alongside cost savings and payback periods. Rock Wool insulation achieved the highest energy savings, while green walls offered modest improvements and passive cooling. Hybrid strategies delivered the best overall performance but resulted in longer payback times. The most cost-effective measure was cavity fill insulation in the 1970s house. By integrating energy and economic assessments across varied building types and retrofit combinations, this study fills a critical gap and advocates for customized, cost-effective retrofit strategies, especially in heating-driven climates where green walls alone yield limited benefits. The insights also extend to international contexts with temperate climates and aging housing stocks, supporting renovation strategies aligned with global decarbonization targets.