Cross-laminated timber
Cross-laminated timber, or CLT, is an engineered wood panel made from layers of lumber bonded at right angles. It lets builders use large prefabricated wood panels for walls, floors, roofs, and other structural parts of mid-rise and tall mass-timber buildings.
What cross-laminated timber is
Cross-laminated timber is a structural panel product made by gluing layers of solid-sawn lumber so that each layer's grain runs perpendicular to the one beside it. The crosswise layout gives the panel strength and stiffness in two directions, which is why CLT can act more like a large plate than a simple wood beam. CLT belongs to the broader mass timber family. Instead of using many small framing members at close spacing, a project can use large factory-made panels that arrive on site ready to be lifted into place.
How the panels are made
Manufacturers dry and grade lumber, arrange boards into layers, apply structural adhesive, then press the stack into a panel. Most panels use an odd number of layers, such as three, five, or seven, so the outside faces run in the same direction. Openings, service chases, edge profiles, and connection holes can be cut by computer-controlled equipment before the panels leave the factory. That prefabrication is one reason CLT buildings can go up quickly when the design, shipping, and installation plan are coordinated early.
Where builders use it
CLT is commonly used for floor plates, roof decks, shear walls, shaft walls, and load-bearing wall panels. It can be paired with glulam beams and columns, steel connectors, concrete foundations, and conventional envelope systems. The material is especially useful when a project wants lighter structural panels, a visible wood interior, or faster enclosure than a fully site-built frame. It is not a universal replacement for steel or concrete; spans, vibration limits, fire ratings, moisture exposure, code rules, and cost all shape whether it is the right choice.
Structural behavior
The alternating layers help CLT distribute loads across a panel and limit the swelling and shrinking that would occur if every board pointed in the same direction. Engineers still have to design the panel thickness, span direction, supports, fasteners, diaphragms, and lateral-force system for the specific building. Connections are a major part of the structure. Screws, plates, hold-downs, splines, and bearing details transfer forces between panels and into beams, columns, or foundations. A strong panel with poorly detailed connections will not perform as intended.
Fire and moisture design
Large timber members do not behave like small sticks in fire. The outside of a massive wood element can char, and that char layer slows the heat reaching the inner wood. Fire design uses tested assemblies, calculated char rates, encapsulation where required, sprinkler systems, and code-approved details rather than assuming exposed wood is automatically safe. Moisture needs the same seriousness. CLT panels should be protected during transport, storage, erection, and service life so water does not remain trapped at joints, penetrations, or concealed layers. Good detailing gives water a path out and keeps long-term wetting away from structural wood.
Why it matters
CLT gives architects and engineers another structural option between light wood framing and heavier mineral or metal systems. Because panels are made from wood, they can store biogenic carbon while the building is in use, and they can reduce construction weight compared with many concrete systems. Those benefits are not automatic. The climate case depends on forest management, manufacturing energy, transport distance, building lifespan, and what material the CLT replaces. The strongest projects treat CLT as part of a whole building system, not as a single green label.
Limitations and tradeoffs
CLT can be more expensive or harder to source in regions without nearby production, experienced installers, or engineers familiar with mass timber. Panels are large, so shipping routes, crane access, lifting points, and site sequencing have to be planned with care. Acoustics and vibration also need attention. A CLT floor that is structurally strong may still need topping layers, resilient mats, ceilings, or other assemblies to meet comfort and sound expectations in apartments, hotels, schools, and offices.