Cross laminated timber

Cross-laminated timber (CLT) (a sub-category of engineered wood) is a wood panel product made from gluing layers of solid-sawn lumber together. Each layer of boards is usually oriented 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 right angles, the panel is able to achieve better structural rigidity in both directions. It is similar to plywood but with distinctively thicker laminations (or lamellae). Cross-laminated timber (CLT) (a sub-category of engineered wood) is a wood panel product made from gluing layers of solid-sawn lumber together. Each layer of boards is usually oriented 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 right angles, the panel is able to achieve better structural rigidity in both directions. It is similar to plywood but with distinctively thicker laminations (or lamellae). CLT is distinct from glued laminated timber, a product with all laminations orientated in the same way. CLT was first developed and used in Germany and Austria in the early 1990s. Austrian-born researcher Gerhard Schickhofer presented his PhD thesis research on CLT in 1994. Austria published the first national CLT guidelines in 2002, based on Schickhofer's extensive research. These national guidelines, 'Holzmassivbauweise', are accredited with paving a path for the acceptance of engineered elements in multistory buildings. Gerhard Schickhofer was awarded the 2019 Marcus Wallenberg Prize for their groundbreaking contributions in the field of CLT research. By the 2000s CLT saw much wider usage in Europe, being used in various building systems such as single-family and multi-story housing. As old growth timber become more difficult to source, CLT and other engineered wood products appeared on the market. In 2015, CLT 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 CLT to be used in the assembly of exterior walls, floors, partition walls and roofs. Also included in the 2015 IBC were char rates for fire protection, connection provisions and fastener requirements specific to CLT. To meet structural performance requirements, the code mandated that structural CLT products met the requirements specified by ANSI/APA PRG 320. The manufacturing of CLT can be split up into nine steps: Primary lumber selection, lumber grouping, lumber planing, lumber cutting, adhesive application, panel lay-up, assembly pressing, quality control and finally marketing and shipping.:77–91