Energy Efficiency of Older Houses: A Parametric Optimisation Study on Retrofitting a 1930s House in Adelaide, Australia

Improving the energy efficiency of Australia’s ageing housing stock is critical to achieving national decarbonisation and climate resilience goals. Although houses built prior to the introduction of national energy efficiency regulations in the 1990s are commonly assumed to be thermally inefficient, empirical evidence for their performance under Australian climatic conditions remains limited, particularly for prevalent pre-war construction typologies. This study addresses this gap by examining the thermal comfort and energy demand of a representative double-brick house built in the 1930s in Ade-laide, Australia. A combined methodology was adopted, integrating long-term envi-ronmental monitoring, occupant responses, and building performance simulations conducted in two stages. The first stage evaluated the existing building’s thermal and energy performance to establish a calibrated baseline, while the second stage applied parametric optimisation analysis to assess potential retrofit strategies. Baseline results indicate that the case-study dwelling exhibits strong passive cooling performance in summer, challenging the prevailing assumption that older Australian houses are in-herently thermally inefficient. Building on this calibrated baseline, parametric optimi-sation of 467 retrofit configurations was undertaken and benchmarked against the Aus-tralian Nationwide House Energy Rating Scheme (NatHERS). The results show that a combined strategy of increased insulation, reduced infiltration, upgraded glazing, and optimised external shading can reduce total heating and cooling loads by up to 78% compared to the original condition, achieving energy ratings of up to 8.5 NatHERS Stars. The findings demonstrate a transferable workflow that links empirical performance as-sessment with simulation-based optimisation for evaluating retrofit options in older housing typologies. For pre-war double-brick houses in warm-temperate climates, the results indicate that prioritising airtightness and glazing upgrades offers an effective and feasible retrofit pathway, supporting informed decision-making for designers, owners, and policymakers.