Evaluating stealth bio thermal wall skins for mould mitigation and hygrothermal performance in urban housing

Abstract

Abstract This study proposes a stealth bio-thermal wall skin as a multi-functional retrofit solution for mould mitigation and passive hygrothermal performance in urban housing. Designed to align with stealth construction principles, the wall system combines prefabricated insulation with a bio-based, mould-resistant coating, promoting low disruption, modularity, and environmental responsiveness. Simulations were conducted in GNU Octave to evaluate heat and moisture transport using a 1D transient model under real climate conditions for five African cities, each representing a diverse urban climate. Mould Growth Index (MGI) was calculated hourly, while annual heat loss and moisture risk indicators were compared between baseline masonry walls and the retrofitted system. Results show that the stealth retrofit reduced heat loss by 42–61% and cut mould-risk hours (RH > 80%) by up to 55%, with clear improvements in interior surface humidity. These findings demonstrate that a single, modular intervention can address both energy inefficiency and indoor air quality, critical issues in ageing, resource-constrained housing. While the model simplifies real-world dynamics, it provides a replicable and scalable approach to sustainable retrofitting in rapidly growing cities. Future work should build on these findings by incorporating airflow dynamics, material ageing, and experimental validation under real-world conditions.