Dynamic Hygrothermal Analysis for Retrofitting Opaque Envelopes in Humid Climates: From Simulations to Guidelines

This paper introduces the dynamic hygrothermal performances of existing walls in humid climates using the EN ISO 15026 procedure. Water content, mould formation and freezing risk were investigated considering rock wool (RW) and expanded polystyrene (EPS) allocated at different points of two typologies of existing walls requiring renovation. Results show that RW is recommended for insulation on the external side, whereas EPS is more suitable for the internal side. A freezing risk occurs in massive walls insulated internally with RW in severe winter climates. Mould formation appears in the initial phases on the renovated side, driven by the built-in humidity of the new layers. Wall thermal transmittance shows large fluctuations, especially in lightweight structures renovated with EPS, reaching an increase of over 22% at the beginning of the heating period, driven by EPS water content peaks of 1.9 kg/m2 in cold climates when installed on the external side, achieved in a stabilized regime and independently from the wall’s technical solution. Outcomes confirm transient hygrothermal analysis as the recommended approach to evaluate the component behaviour over a long-term projection, facilitating sizing in the design phase and ensuring compliance with regulations for retrofitted elements.