Cross-laminated timber, or CLT, is made by gluing layers of dimensional lumber together at alternating ninety-degree angles, producing a panel with structural strength in both directions — closer in behavior to a slab of concrete than to a conventional stick-framed floor. That panel behavior is what's letting the material move into mid-rise construction, five to twelve stories, that would traditionally default to steel or concrete.
The panels are manufactured off-site to exact dimensions from a building's digital model, including pre-cut openings for stairs, elevators, and mechanical penetrations, then shipped to the job site ready to install. A mid-rise structure that would take months to form and pour in concrete can go up in a matter of weeks in CLT, since there's no formwork and no cure time on site.
A CLT floor plate arrives on site already finished on one face. You're not building it — you're installing it.
Embodied carbon is the material's other major selling point. Wood sequesters carbon as it grows, and manufacturing CLT requires far less energy than producing an equivalent volume of concrete or steel, which together give a CLT structure a substantially smaller carbon footprint at the point of construction, before any operational energy is even considered.
The material isn't without real limitations. Fire performance requires careful detailing — thicker panels char predictably and can be engineered to maintain structural capacity through a fire rating, but the detailing at every panel-to-panel and panel-to-steel connection has to be resolved specifically for CLT, since the standard connection details from concrete or steel construction don't transfer directly.
Acoustic performance between floors is the other recurring challenge, since a mass timber floor transmits impact noise differently than a concrete slab. Most CLT mid-rise projects now include a topping layer and a resilient underlayment specifically to address footfall noise, an extra assembly layer that adds cost but has become close to standard practice.
