North American cross laminated timber is currently made of softwood lumber following the guidelines of the ANSI/APA PRG-320 manufacturing standard. In this study, the potential of manufacturing CLT panels using various hardwood species and engineered wood products (EWP) was investigated for their compatibility and the impact on the dimensional stability and aesthetics of the end products. Yellow birch, trembling aspen, sugar maple, laminated strand lumber (LSL) and laminated veneer lumber (LVL) were compared to 100% spruce-pine-fir group species (SPF) lumber made CLT panel. The bond line performance of the assemblies was tested as well as the dimensional stability and appearance of the panels when subjected to conditions with equilibrium moisture contents (EMC) of 4.5%, 12% and 16%. Results showed that higher density hardwood species were prone to delamination. LSL, LVL and trembling aspen yielded promising delamination results. Best overall dimensional stability results were achieved with EWP inclusive configurations. Aesthetic integrity assessment showed that the use of hardwood for the core layer and edge gluing of softwood outer layers had a negative impact. Overall, the study showed a great potential for manufacturing future composite CLT (CCLT) products using EWP and low density hardwood species. The cost premium of using these alternative materials would need to be offset by valuable sets of properties or by a reduction of the manufacturing cost.
Cross Laminated Timber (CLT) is a new wood-based material composed of cross laminated wood boards that form a structural panel. This study focuses on identifying the appropriate methods to determine the hygrothermal properties of CLTs fabricated with Canadian and European Lumber. The laboratory tests carried out in this study will help establish heat, air and moisture response properties to be used for hygrothermal simulation to assess the durability of CLTs in building envelope construction.
Measurement of water vapour permeability, liquid water absorption, sorption isotherms, thermal conductivity, and air permeability were performed on three Canadian CLT specimens composed of Hem-Fir, Eastern Spruce-Pine-Fir, and Western Spruce-Pine-Fir and one European specimen composed of Spruce.
The hygrothermal properties of CLT, considered in this study, appear to be similar to commonly used wood specimens reported in the literature. However, liquid water absorption coefficients of CLT were found to be generally lower than common wood species, possibly due to the presence of glue between the wood layers which limits the moisture movement across the specimen. On the other hand, the air permeability across the CLT specimens varied due to the glue discontinuity within the specimen which led some CLTs to be permeable, however all the European specimens were found to be impermeable.
This study also critically analyzed the significance of equilibrium moisture content (EMC) of wood at high relative humidity, measured by means of a pressure plate apparatus and humidity chambers, on the moisture management performance of a wood-frame stucco wall, using thehygrothermal simulation tool hygIRC-2D. The simulation results indicate that the prediction of the moisture response of a wood-frame stucco wall assembly depends significantly on the method adopted to derive the EMC of wood at high RH.
The evaluation of damages in large-span timber structures indicates that the predominantly observed damage pattern is pronounced cracking in the lamellas of glued-laminated timber elements. A significant proportion of these cracks is attributed to the seasonal and use-related variations of the internal climate within large buildings and the associated inhomogeneous shrinkage and swelling processes in the timber elements. To evaluate the significance of these phenomena, long-term measurements of climatic conditions and timber moisture content were taken within large-span timber structures in buildings of typical construction type and use. These measurements were then used to draw conclusions on the magnitude and time necessary for adjustment of the moisture distribution to changing climatic conditions. A comparison of the results for different types of building use confirms the expected large range of possible climatic conditions in buildings with timber structures. Ranges of equilibrium moisture content representative of the type and use of building were obtained. These ranges can be used in design to condition the timber to the right value of moisture content, in this way reducing the crack formation due to moisture variations. The results of this research also support the development of suitable monitoring systems which could be applied in form of early warning systems on the basis of climate measurements. Based on the results obtained, proposals for the practical implementation of the results are given.