Moisture-Related Risks in Internally Insulated Historic Field Stone Masonry Walls: A Long-Term Hygrothermal Assessment Under Past and Future Climate

Improving the energy efficiency of historic field stone masonry buildings often requires internal insulation, as external insulation is frequently restricted by heritage and architectural constraints. Internal insulation, however, alters the hygrothermal behavior of massive masonry walls and may increase moisture-related risks. This study assesses the hygrothermal performance of an internally insulated historic field stone masonry wall under past and projected future climatic conditions using long-term transient simulations. Coupled heat and moisture transfer simulations were performed with the DELPHIN software for an uninsulated reference wall and an internally insulated configuration. The analyses accounted for wind-driven rain, masonry heterogeneity, and variations in inner core composition. Past conditions were represented by a continuous 20-year measured climate dataset, while future conditions were evaluated using regional late-century climate projections (RCP2.6 and RCP8.5). Hygrothermal performance was evaluated based on moisture mass density, freeze–thaw exposure, and mold-relevant temperature–relative humidity conditions at predefined evaluation points within the wall. The results show that moisture accumulation develops gradually and cannot be reliably captured by short simulation periods. Internal insulation redistributes moisture-related risks within the wall rather than fundamentally altering the seasonal moisture regime. Freeze–thaw exposure occurs under all investigated climates, while mold-relevant humidity conditions persist at interior-adjacent locations. The findings demonstrate the importance of multi-year hygrothermal analyses when assessing moisture-related risks in internally insulated historic masonry walls.