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Glued laminated timber (GLT) is a structural timber made by gluing individual timber slabs together under certain conditions. It offers more efficient use of wood, higher structural strength, better fire resistance, and more aesthetically pleasing architectural designs, making it widely used in public buildings such as libraries, schools, visitor centers, and swimming pools. In Canada, three main tree species are commonly used for GLT production: SPF, Douglas fir, and western hemlock. These three high-quality timbers, combined with advanced processing techniques, allow for the creation of various GLT products and curved and straight shapes, providing architects with design freedom and enabling the realization of innovative timber-framed buildings.
SPF (Spruce-Pine-Fir)
Canada's vast forests produce some of the world's finest softwood timber. SPF trees are medium-sized, averaging 26 meters in height and up to 80 centimeters in diameter. They are hardy species, and due to their slow growth in northern climates, they develop beautiful grain patterns, a clean and bright appearance, and colors ranging from white to light yellow. Almost all SPF timber undergoes kiln drying to reduce its moisture content to below 19%. This not only prevents staining and increases the timber's strength and hardness, making it more resistant to dents, bending, and cracking, but also improves its workability, making grooving and drilling easier. It has excellent gluing properties, strong nail-holding power, and is suitable for painting and staining. Kiln-dried SPF timber is lightweight, stable, easy to work, has a beautiful grain, and is readily available, making it an ideal choice for construction and structural materials.
Douglas fir
Canadian Douglas fir is characterized by its light-colored, narrow sapwood, while the heartwood ranges from yellow to reddish-brown. The earlywood and latewood show a clear color distinction, with the latter exhibiting more pronounced, darker bands. This color variation results in different grain patterns when sawn flat. The wood has a fine to medium texture with a straight, dense grain. Douglas fir is the strongest of all Canadian conifers. It has high bending and breakage resistance, as well as high rigidity. It also has high hardness and abrasion resistance. Douglas fir dries relatively easily with a low likelihood of cracking during drying and exhibits good dimensional stability. It has good machinability. Douglas fir has good bonding properties, moderate nail-holding power, and absorbs paints and stains well.
Western Hemlock
Western hemlock from Canada is light-colored, pinkish, or reddish-brown. It has clear growth rings with a subtle transition between earlywood and latewood. The grain is straight and even, and the wood is medium to fine-grained. Its shade tolerance allows it to self-break branches during growth, a characteristic that makes it easy to produce large quantities of defect-free timber. Hemlock is dimensionally stable after air-drying or kiln-drying and gradually hardens during drying and aging, resulting in excellent wear resistance throughout its lifespan. Hemlock has excellent workability and is easy to machine. Because of its hardness and straight grain, it is easy to plan and does not crack. Hemlock has excellent nail and screw holding power. The surface of hemlock wood is smooth and resin-free, allowing it to absorb various paints and stains. Western hemlock can be treated with preservatives and fire retardants and has good chemical treatment properties, making it a preferred species when high-strength and high-density treated timber is required.
SPF, Douglas fir, and western hemlock, with their inherent advantages in strength and appearance, can be processed into standard and non-standard sizes. Standard-sized lumber facilitates assembly, optimizes wood usage, is economical, and easy to transport, while non-standard lumber requires customization. The pre-laminated panels used to make glulam consist of dried, graded, and longitudinally finger-jointed standard-sized lumber. For straight glulam, the pre-laminated panel thickness is typically 35–50 mm; for curved glulam, the thickness is typically 20–30 mm.
Energy conservation and environmental protection, as important concepts of sustainable development, are receiving increasing attention and recognition. Modern timber-framed buildings, which are gradually becoming a new hot topic, have unparalleled advantages in energy conservation and environmental protection because the timber they use not only improves the natural environment during its growth but also has low energy consumption during processing, is biodegradable after disposal, and has good thermal insulation properties when applied to projects. As a result, the construction industry has placed them in an important position for green and sustainable development.