Cross-laminated timber (CLT) is a relatively new, large structural panel product composed of multiple layers of dimension lumber held together with adhesives. It is used in walls, floors and roofs in residential and non-residential construction. It has also been used in bridges, as platforms for oil rigs, and to construct tall timber structures of over five storeys. CLT offers a renewable alternative to concrete and steel systems.
The grain of each layer of lumber is placed at a right-angle to adjacent layers (similar to the arrangement of veneers in plywood). An odd number of layers is normally used (to decrease warping), and nails or screws may be used for added strength. CLT can be produced in large sizes (up to 0.5 metres thick, 4 metres wide and 24 metres long) into which door, window and service openings can be machined.
As a prefabricated building component, CLT offers shorter on-site construction time than traditional platform-frame or steel and concrete construction systems. It also stores carbon, in the form of wood, for the life of the building and even longer if the CLT is reused or recycled when the building is decommissioned.
Lower-quality lumber is sometimes used for the interior layers of CLT, while higher-quality, more visually appealing lumber is used for the outer layers. This can provide an economic use for wood degraded by pests and disease, such as wood from trees attacked by the mountain pine beetle in western North America. It also provides large-scale carbon storage for mid-rise buildings that typically contribute substantially to the carbon footprint of a given region.
CLT is a relatively new product in North America, with just a few small production facilities. Because of its size, stability, fire safety performance and structural properties, it has good potential for use in mid-rise construction (theoretically up to 24 storeys) for walls, floors and roofs. Research is now underway in areas such as fire resistance, connections and seismic performance to ensure its performance, so that building codes can be safely changed to allow the use of CLT in construction. Currently, much of the CLT produced is used in platforms for oil rigs and for demonstration buildings.
While it is too soon to predict future markets, the general trend toward replacing non-renewables with more sustainable materials and the need to lower carbon footprints suggest increased use of CLT in the future.
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