CLT panels – fast and natural alternative to concrete

Cross-laminated timber also known as CLT, X-lam, BSP or Cross-Lam or other trade names, is a cutting-edge timber material for construction. Cross laminated timber panels combine the best structural properties of wood with a natural aesthetic and safety. Panels are made of spruce boards glued in perpendicular layers, ranging from three to eight layers. Formaldehyde free PUR adhesive makes the panels extremely durable and safe for living. CLT wood house can even be a high rise building since CLT panels can bear very high loads.

CLT – use and specification of panels

Cross laminated timber is mainly used as a homogenous load-bearing element for walls, floors/ceilings and roof elements in all types of buildings. This material is also used for interior elements such as stairs or design furniture.

The dimensions of CLT panels are calculated individually for each project, based on the parameters of the building and client’s wishes. Maximum dimensions of a cross laminated timber panel are 13 800 x 3100 x 400 mm. The wooden surfaces can be left exposed if desired in which case a smoother sanded finish is applied. In structural calculations CLT is equal to C24 grade and weighs 5.0 kN/m3.

CLT panels are a lightweight construction material and are at least 3 times lighter than lightweight concrete or almost 5 times lighter than regular concrete. This makes it very convenient for transportation to the construction site and handling during installation on-site therefore requiring less machine and manpower.

CLT panels excel in fire safety characteristics, proving to be better performing than even metal and concrete. This is because the dense wood heats up much slower during a fire compared to metal or concrete. Also massive timber burns with predictably slow. Charring rate is 0.65 mm/min. Therefore the deterioration of structural properties is slow and predictable unlike metal and cocrete.

Finished panels

CLT material can be used to produce wall, floor or roof panels. Panels have various make up depending of the architectural requirements of the client, structural and technical requirements of the project. Therefore a layer of insulation is usually added to gain a high grade of thermal insulation properties. Wall panels can be finished on the outside with various kinds of siding depending on the project and architecture. The siding can be board siding, plaster, various slab materials etc. Inside of a wall panel can be left to expose CLT in which case the plan for wiring and sockets must be adjusted to the technical capabilities of drilling channels and openings into the panel. Inside of a wall panel can also be covered with gypsum boards to add a service area for wiring and plumbing.

Frequently asked questions about CLT

CLT is used for its strength and also for its aesthetic and environmental advantages. CLT is mostly used in buildings where larger spans are required and it can be used successfully in single family homes for that purpose or where the owner wants to enjoy the texture of exposed mass timber in the interior. Where there is no such requirement it makes more economical sense to build in timber frame. Exterior walls with CLT panels need insulating and cladding. ZTC specializes in providing a full installation kit and installation works not just delivering panels.

CLT panels are made in different panel thicknesses depending on structural requirements. Standard panels are made of at least 3 cross laminated layers of boards and thickness can be varied from 60 mm to 160 mm with 5 layers.

CLT surface has the properties of massive wood. Panels can be ordered pre-sanded in the factory if they are to be used exposed in the interior. Channels for electrical conduits and boxes can be drilled and routed at the factory. Interior surface can also be covered with a service layer and drywall. Exterior walls are insulated and cladded on the outside.

CLT is made from wood that is glued with polyurethane glue that does not emit any off-gassing of volatile organic compounds while concrete and many binders in masonry emit VOCs during curing. There have been extensive tests for fire resistance of CLT and it outperforms concrete and metal structures due to the fact that massive timber burns slowly and predictably and forms a char insulating layer compared to steel and concrete that rapidly lose their load bearing capacity at high temperatures.

CLT is not a EN standardized building material therefore it is not required to be CE marked. It can be voluntarily certified with a European Technical Assessment (ETA) to provide evidence of its appropriate production and use. ZTC provides ETA certified CLT panels.