Abstract

The infiltration of rainwater can result from envelope defects that allow water to infiltrate into the stud cavity behind the exterior sheathing, i.e. the back wall. Once rainwater migrates into the stud space, it cannot easily evacuate and is thus likely to accumulate, leading to potential degradation of the wood studs and exterior sheathing, depending on the temperature conditions. Therefore, studying the drying potential of wood-frame wall assemblies that have been subjected to a moisture load like rain infiltration can provide valuable information with respect to the assembly's hygrothermal performance. The primary objectives of the research project were: (1) To evaluate the wetting and drying performance of hygroscopic components in wood-frame wall assemblies wetted by rain infiltration; (2) To investigate the impact of several parameters on the hygrothermal response of the various monitored components such as the sheathing material, the type of vapor retarder, and the presence of foam insulation on the exterior side of the assembly, (3) To develop a framework for large-scale envelope testing of wall assemblies subjected to wind-driven rain infiltration. The role of the vapor retarder, the exterior insulation, an added exterior insulation, the wall height, the presence of hygroscopic cladding was studied and the effect of varying the moisture load was also investigated. The research was primarily experimental but also included some simulation work. The moisture content results from the experiments show that the sheathing material had the most significant impact on the drying response of the wall components, with the lowest and highest drying rate occurring when OSB and fiberboard sheathings were employed, respectively. Increasing the vapor permeability of the vapor retarder within the range allowed by the National Building Code of Canada increased the drying rate of the wetted components within the walls when OSB sheathing was employed. Comparison of the experimental and numerical results highlighted the difficulties in simulating a three-dimensional problem in a two-dimensional domain, the need for accurate and complete material properties, and the need to include of all relevant transport phenomena like air transport in hygrothermal envelope models to increase the accuracy of the simulation results