Cross laminated timber
Cross laminated timber (CLT), BSP, also KLH in German, is a solid wood construction material produced out of at least three crosswise glued layers. The layers each consist of one-ply slat boards. According to the same principle as veneer plywood, the crosswise construction enables a high dimensional stability: Each wooden layer prevents dimensional stability changes to the individual boards from humidity deviations in the wood in the neighbouring layer that is at a right angle to the others.
CLT is mainly used as a ceiling and wall element in timber construction. It is also used in temporary path construction, such as when harvesting oil and gas away from paved ways (rig mats). In residential construction, as well as in building and industrial construction, it is used as statically load-bearing and non load-bearing elements. CLT can be used not only for outer and interior wall construction, as well as roof and ceiling elements, but also for staircases and balcony slabs. It is frequently used for extensions on top of existing buildings because of its low weight. Insulation, facing shells, and facade elements can easily be attached to CLT.
CLT can also easily be combined with other materials, for example concrete. This makes it an ideal material for multi-storey wooden construction. In Vancouver, Canada, you can currently find the highest house made of CLT (March 2018). It is 18 storeys and 53 m high. Panels with three to seven layers and a total thickness of up to around 50 cm are customary. It is possible to produce panels up to 18 m in length and 3 m in width. Other common names on the market are KLH, thick wood or X-Lam.
If it is planned, built, and protected against weathering and humidity in the correct way, a CLT building can last for centuries. The CLT market is growing incredibly dynamically all over the globe. In 2016, production capacity was around 800,000 m³. The aim is to increase this by around 2 million m³ by 2020. In 2017 alone, at least 30 new production sites were built.
CLT is made of board slats, just like plywood boards, that have been dried to a certain wood humidity. Typical construction wood is used, e.g. conifers, such as spruce, pine, Scots pine, larch or Douglas fir tree. In rare cases, deciduous wood is used.