The importance of material specific data in the hygrothermal modelling of traditional solid walls and its impact on the evaluation of retrofit strategies

The thermal retrofitting of buildings is widely recognised as a crucial strategy for mitigating CO 2 emissions. In Ireland, approximately one-sixth of the existing building stock predates 1945, comprising heritage buildings with distinct upgrading requirements to preserve both their special heritage character and material fabric. Hygrothermal modelling tools such as WUFI are commonly employed to assess the moisture response of traditional walls and assist in selecting appropriate thermal upgrade strategies. The accuracy of these models relies heavily on input variables, with one of the primary uncertainties being the selection of materials from the database that most accurately reflects the in-situ properties of the historic wall. This research compares the moisture behaviour of two Irish historical bricks, whose properties have been measured in the laboratory, with two default bricks selected from the WUFI database. The study evaluates the divergence between their modelled performances and illustrates that certain insulation materials and different thicknesses may be considered suitable in some cases but not in others, depending on the type of brick chosen for modelling, and highlights the relationship between the Free Saturation value of a brick and its simulated moisture profiles. For the modelled insulated scenarios with high internal humidity, calcium silicate board poses a lower moisture risk compared to cork-lime. The study aims to enhance the precision and reliability of hygrothermal models used in the context of thermal retrofitting strategies for heritage buildings. This research is part of the FabTrads-TradFabs series of projects measuring the hygrothermal properties of traditional Irish building materials.