Experimental and numerical assessment of rainwater intrusion in ventilated facades with open joints

Rainwater ingress is the primary source of premature degradation of building materials. However, currently little quantitative information is available on rain water management of wall systems in general, and ventilated facades in particular: how much water infiltrates, how much water crosses the cavity, and what is the impact on the hygrothermal performance? To understand the water and moisture management of ventilated façades with open joints, experimental watertightness tests were conducted to assess the impact of cavity depth, width of the panel joints, out-of-plane installation of panels, and dimensions of supporting structure. A test setup was designed to quatify the rainwater infiltration in the wall cavity. Subsequently, an experimental study was done on the rainwater infiltration into the insulation layer for different materials (PU and mineral wool), airtightness level, and workmanship (with and without common deficiencies). The results from both test series were then used to simulate the impact of rainwater ingress on the hygrothermal behavior by means numerical simulations. 1D hygrothermal simulations were conducted for ventilated facades located in Brussels (Belgium), Bergen (Norway), and Lisbon (Portugal). The risk for mold problems is small as the drying potential due to the ventilated cavity is large. However, infiltration may have a significant impact on the latent heat transport and annual heat flux. For a cavity of 40 mm the increase in heat flow is limited to 0.4%, whereas for a 20 mm cavity the increase rises to 10.5%. The installation of a WRB reduces the infiltration of water into the insulation, but the effect of installation errors also increases due to reduced drying potential.