Influence of liquid absorption coefficient on hygrothermal behaviour of an existing brick wall with Lime–Hemp plaster

• The paper analyzes a brick wall covered with Lime–Hemp plaster.
• The analysis combines hygrothermal simulations and experimental planning method.
• Neglecting absorption coefficient of materials can lead to unrealistic results.
• Liquid absorption has greater influence on the results than vapour permeability.
• The paper helps to choose appropriate material based on these two parameters.

The study of the hygrothermal parameters and performance of permeable materials is being expanded; however, there is a lack of guidelines or regulation regarding the level of liquid water migrations associated with existing materials. Even if some existing recommendations demand the installation of materials that are increasingly permeable to vapour, the liquid water absorption coefficient is often neglected. This study analyses the influence of six material parameters, such as the liquid absorption coefficient and vapour diffusion resistance, on the hygrothermal behaviour of an existing brick wall insulated on the inside surface with a Lime–Hemp plaster. A specific methodology is developed combining hygrothermal simulations, sensitivity analysis and an experimental planning method. This reproducible methodology allows recommendations to be proposed to help designers choose an appropriate combination of material parameters. The paper demonstrates that the water liquid absorption coefficients of brick and of insulation have a greater influence than the vapour diffusion resistance of those materials in the studied cases. Water liquid absorption coefficient should thus be one of the parameters systematically considered in the hygrothermal analyses of wall components.