Hygrothermal performance of hydrophobized and internally insulated masonry walls: Simulating the impact of hydrophobization based on experimental results

Buildings are accountable for around 40% of the European energy consumption. Installing thermal insulation is an effective approach to improve the energy efficiency of the building envelope. Internal insulation is often the only renovation option in the case of historic buildings with worth-preserving masonry façades. However, it can lead to several moisture problems related to the rain load, such as mould growth, wood rot and frost damage. Hydrophobizing the façade reduces water absorption by the materials, while decreasing their drying rate, threatening the desired outcome. The paper evaluates the impact of hydrophobization when combined with internal insulation. To understand the hygrothermal effect of hydrophobization on internally insulated walls, it is important to examine how the hydrophobic layer of the masonry can be accurately modeled and how the hygrothermal response of the wall configuration changes after treatment. A significant increase in the thermal conductivity of capillary saturated samples compared to dry samples was experimentally measured. The hydrophobic model is able to predict the hygrothermal behavior of the hydrophobized brick, using experimental results from water uptake and drying tests as reference, as well as in the component level, using as reference relative humidity and temperature measurements in a mock-up wall. The current results indicate that hydrophobization contributes positively towards a moisture-safe construction with reduced heat losses when applied before or in parallel with internal insulation. These findings confirm that hydrophobization can successfully be combined either with a capillary-active or a water-vapor-tight internal insulation system, providing a moisture-safe energy renovation of building enclosures.