Preliminary Characterization of Physical Properties of Cross-Laminated-Timber (CLT) Panels for Hygrothermal Modelling

Cross-laminated-timber (CLT) panels are a type of relatively new wood-based structural panel, typically manufactured by laminating three or more layers of lumber together, with each layer rotated 90° relative to the neighbouring layers. This study explored preliminary assessment of the physical properties of a range of specimens for the purpose of initiating generating material property data for hygrothermal simulation of CLT building enclosure assemblies. Three types of five-layer CLT panels (nominally 130 mm thick) were made with Canadian softwood species, including spruce-pine-fir (SPF) from Eastern Canada and British Columbia, and hem fir from British Columbia, all glued with emulsion polymer isocyanate (EPI) as the adhesive applied between neighbouring layers. One type of three-layer CLT (nominally 90 mm thick) commercially manufactured in Europe using European spruce, with polyurethane adhesive, was also tested. Physical properties including density, thermal conductivity, liquid-water absorption, water-vapor permeability, sorption (moisture storage function), and air permeability were measured, mostly based on established international standards. To assess the impact of the adhesive on the hygrothermal properties of CLTs, test specimens used for most tests included at least one layer of adhesive, except those used for sorption tests, which used very small specimens. The properties were expected to mostly reflect the properties of the lumber used for CLT manufacturing. Variations in properties were found among these different CLT specimens; however, it was generally concluded that the differences caused by wood species and manufacturing methods would not be large enough to cause considerable differences in the hygrothermal properties or significantly impact the outcomes of hygrothermal simulation. With small-scale testing and very limited replication this study showed that the water-vapor permeability of CLT generally increased with an increase in relative humidity (RH), and the air permeance of the CLT specimens without visible gaps and checks was negligible.