Analysis of Retrofit Strategies of Mid-20th-Century Modern, Concrete Buildings

Reusing existing buildings is a valid response to the architectural challenge associated with addressing climate change and can aid the regeneration of the historic built environment. This demands sensitive architectural conservation strategies that improve thermal comfort, indoor environmental quality, and energy efficiency. In addition, energy retrofit solutions that balance performance improvements with the conservation of cultural and architectural values are needed to achieve higher performance while preserving cultural heritage, architectural features, and identity. Energy retrofits of post-war, mid-20th-century buildings pose particular challenges, including low ceiling heights, full-height windows, external decorative components, and other structural aspects, as these features hinder thermal upgrades. Concrete buildings from this period are frequently demolished due to limited guidance on effective retrofit methods. This study explores the most effective energy retrofit strategies for balancing energy efficiency with conservation requirements in such buildings, and assesses the risks associated with condensation and thermal bridging arising from internal insulation strategies. This paper examines internal insulation as a retrofit solution, where external insulation is not feasible. Internal wall insulation (IWI) reduces overall heat loss but concentrates thermal transfer at uninsulated junctions, thereby increasing the risk of condensation. In the simulated case, a relatively thin, short strip of slab insulation, combined with wall insulation, significantly reduced condensation and mould risk, suggesting a potential solution for mid-century building types. The analysis shows that applying insulation asymmetrically worsens conditions on the uninsulated side. Full-height window replacement, coupled with internal slab insulation, results in the most significant improvement; however, slab insulation alone can mitigate condensation risks where window replacement is not permitted. Findings highlight that partial insulation at balconies, parapets, and roof junctions is minimally effective, reinforcing the importance of integrated internal strategies for successful retrofits.