ABSTRACT
Moisture accumulation in the building envelope poses a serious threat to the integrity and durability of the assembly. Rain can be a significant source of such moisture when it penetrates at defects in envelope junctions such as the interface between walls and windows. To understand the mechanism at play in the wetting/drying of assemblies, most previous laboratory hygrothermal building envelope tests have originally focused on wetting due to water vapor diffusion, then convection, and finally, water infiltration. This is partly due to the complex nature of the rain infiltration process and the associated difficulties with its simulation in the laboratory. Tests that simulate rain have either used a spray rack or similar apparatus to simulate water impinging on a building façade, or introduce water directly into the test assembly. An experiment was designed and is being conducted where a test hut containing 21 wood-frame test wall panels typical of North-American current residential construction was built within a large-scale environmental chamber. The test panels are subjected to simulated rain penetration where water is introduced on the inside surface of the sheathing where the quantity, duration and frequency reflect water infiltration through a window defect for Montreal weather patterns. One of the experimental objectives was to determine the amount of moisture accumulated in each panel during the wetting phase. This paper gives an overview of the experimental methodology for the simulation of rain penetration for building envelope testing, which involves characterization of water leakage through a given envelope defect, as well as determination of the amount of water impinging on a given façade location using results of previous driving rain evaluation by others and local climatic data.
