Abstract

The climate in southern coastal British Columbia (BC) is characterized by a long rainy winter. Building envelope failures that have occurred in recent years in this region promoted the adoption of the rainscreen principle in both rehabilitation and new construction and are now mandatory in the wet regions of Be. In addition to the functions of a capillary break and drainage, drying in an air cavity behind the cladding of the rainscreen wall system may occur through cavity ventilation. Current practice varies in terms of cavity depth and vent heights for rainscreen walls clad with panel systems, especially with respect to the top slot vents. The awareness of potential drying provided by cavity ventilation initiated the idea of providing top vents on brick veneer walls recently in the BC construction industry. However, there exist different views on the drying provided by cavity ventilation based on existing research. Whether cavity ventilation would be beneficial for this climate remained open for discussion. To answer this question, a comprehensive research program was designed by Dr. Hua Ge with the candidate using a two-storey building envelope test facility at British Columbia Institute of Technology (BCIT) which Dr. Hua Ge developed. The candidate investigated twelve wall specimens, six clad with brick veneer and six clad with fibre cement panels, installed on the southeast façade, which faced the prevailing wind-driven rain direction. The test variables include cladding type, air cavity depth and height, vent configurations and initial moisture load in plywood sheathing to evaluate the impact of cavity ventilation on the drying and wetting of test walls. The hygrothermal conditions across the wall assemblies were monitored for moisture content (both resistive and gravimetric), temperature, relative humidity, air speed in the cavity and pressure differentials between top and bottom of each cavity. The on-site weather conditions were measured including wind speed, wind direction, solar radiation, horizontal rainfall, and wind-driven rain. Indoor conditions were controlled at 22±1°C and 55±5% RH In this study, the drying and wetting rates of plywood sheathing in the test walls during the winter and spring seasons were quantified, under-cooling effects on the temperature of cavity-surfaces of claddings and plywood sheathing were analyzed and the daily hours of condensation on the cavity-surface of claddings for all test walls were calculated. Simulation and measurements of MC in plywood sheathing for two brick veneer walls and two fibre cement walls were compared.