The Effects of Simulated Canadian Indoor Cyclical and Seasonal Relative Humidity on Cross-laminated Timber and Glue-laminated Timber

Mass timber samples were acquired from Canadian manufacturers, and they were subjected to controlled relative humidity environments that simulated daily and seasonal trends in Canadian indoor environments. Moisture content and dimensional changes were monitored by physical measurements and by microscope analysis. At high relative humidity, glue-laminated timber showed similar performance to dimensional wood, suggesting the adhesive does not interfere with swelling and shrinkage. In identical high relative humidity, cross-laminated timber exhibited behaviours attributed to moisture-induced stresses caused by the cross-orientation of the layers, with two types of permanent failures at the glue joints: tearing of the wood fibres next to the adhesive and failure of the adhesive, most notably at high relative humidities. These failures were not observed during short-term fluctuations (simulating showers in a bathroom) and seasonal changes in relative humidity.