CLT stands for Cross-Laminated Timber. It is not plywood, not chipboard and not glulam either: it is a large structural panel made of layers of solid sawn timber laid on top of one another — a building element from which an entire wall, floor or roof plane is produced in one piece.
What turns a timber panel into a load-bearing structure?
The secret is in the cross-lamination. During manufacturing, 3, 5, 7 or even 9 layers of solid boards are stacked so that the grain of each layer is rotated by 90 degrees relative to the one below, and the layers are then pressed together under high pressure.
Timber is exceptionally strong along the grain but weak across it, and it also moves mainly across the grain as its moisture content changes. The cross-laminated build-up cancels out exactly these two weaknesses: the panel becomes load-bearing in both directions, and the layers restrain each other's movement, so it stays dimensionally stable.
In practice this means that a single CLT panel acts at once as the load-bearing structure, the bracing and the internal surface — there is no separate frame, separate infill and separate lining.
Strong, but light
Relative to its own weight, CLT carries an exceptional load. It is far lighter than a reinforced concrete structure of the same capacity, which has three very tangible consequences:
- Smaller foundations. A lighter superstructure transfers less load to the ground, so the foundations can often be simpler and cheaper.
- Easier transport and lifting. The panels can be craned into place in a matter of days.
- Larger clear spans. Fewer intermediate supports are needed, so the floor plan is freer.
And fire? — the most common question
This is where most of the myths live. Solid timber does not behave in a fire the way a thin batten does: its surface chars, and that charred layer insulates and protects the sound timber behind it. Burning therefore advances inwards slowly, at a predictable rate — which is why the fire resistance of the structure can be calculated, exactly as it is for a steel or concrete structure.
Steel, by contrast, loses its load-bearing capacity relatively suddenly above a certain temperature. A properly engineered CLT structure is therefore not "more dangerous" than a traditional one — it simply behaves differently, and the profession knows that behaviour well.
How does it differ from traditional masonry?
- Dry construction. There is no curing time and no built-in construction moisture that has to dry out.
- Millimetre precision. Panels are cut on a CNC machine; openings, service penetrations and connections are already in place when they leave the factory.
- Less time on site. Erecting the structure is measured in weeks, not months.
- Stored carbon. The timber stores the carbon dioxide it absorbed while growing for the entire service life of the building.
Who is it for?
CLT really shows its strengths where precision, speed and predictable energy performance are the goal. For a family house that means a shorter build and running costs you can plan for; for an apartment building, the light structure and large spans give freedom.
One thing is worth knowing: the technology works well from the design stage onwards. A CLT house cannot be altered "as you go" the way a masonry structure can — but that same discipline is exactly what makes the result precise and the budget keepable.
