Cross-laminated timber (CLT) is a wood panel product made from glueing layers of solid-sawn lumber together. Each layer of boards is orientated perpendicular to adjacent layers and glued on the wide faces of each board, usually in a symmetric way so that the outer layers have the same orientation. An odd number of layers is most common, but there are configurations with even numbers as well (which are then arranged to give a symmetric configuration). Regular timber is an anisotropic material, meaning that the physical properties change depending on the direction at which the force is applied. By gluing layers of wood at perpendicular angles, the panel is able to achieve better structural rigidity in both directions. It is similar to plywood but with distinctively thicker laminations.
CLT is distinct to glued laminated timber, a product with all laminations orientated in the same way.
Cross Laminated Timber was first developed and used in Germany and Austria in the early 1990s, but it was only after the mid 1990s more extensive research was completed. By the 2000s CLT saw much wider usage in Europe, being used in various building systems such as single-family and multi-story housing. The main reasons behind the rise of Cross Laminated Timber were because of its sustainability and lack of detrimental effects to the environment, but also improved marketing and availability.
USA Building Codes
In 2015, Cross Laminated Timber was incorporated into the National Design Specification for wood construction. This specification was used as a reference for the 2015 international building code, in turn allowing CLT to be recognized as a code compliant construction material. These code changes permitted Cross Laminated Timber to be used in the assembly of exterior walls, floors, partition walls and roofs. Also included in IBC 2015 were char rates for fire protection, connection provisions and fastener requirements specific to Cross Laminated Timber . To meet structural performance requirements, the code mandated that structural CLT products met the requirements specified by ANSI/APA PRG 320.
CLT has various benefits making it an attractive as a building material. These benefits include:
- Design flexibility – CLT has many applications. It can be used in walls, roofs or ceilings. The thickness of the panels can easily be increased by adding more layers and the length of the panels can be increased by joining panels together.
- Eco-Friendly – Cross Laminated Timber is a green and sustainable material since it is made out of wood and does not require the burning of fossil fuels during production.
- Prefabrication – Floors or walls made from Cross Laminated Timber can be fully manufactured before reaching the job site, which decreases lead times and could potentially lower overall construction costs.
- Thermal insulation – Being made out of multiple layers of wood, the thermal insulation of CLT can be high depending on the thickness of the panel.
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