What are some innovative uses of laminated timber in construction?
The Wood Guide · Do it yourself
MaterialLaminated timber in construction
Several layers of wood glued together under pressure into beams and panels that are stronger than the tree they came from. And that are now being used to build towers.
- Glulam and CLT
- Stronger than solid timber
- High-rise in timber
Why laminating makes it stronger
In a solid beam the weakest spot sets the strength: one big knot and the beam breaks there. Glue thin lamellas together and that knot sits in one layer out of twenty — the other nineteen carry the load.
Click a chapter or use the arrows · schematic drawings, not to scale.
Why laminating makes it stronger
It sounds counter-intuitive: saw wood into pieces and glue it back together, and it becomes stronger. Yet it is true, and the reason is statistics.
In a solid beam, the weakest spot determines the strength of the whole. One large knot in the wrong place, and the beam breaks there. Saw that same log into thin lamellas and glue them back together, and that knot sits in one layer out of twenty — the other nineteen take up the load.
On top of that, lamellas can be graded: the strongest layers at the top and bottom, where the stress is highest, and the weaker ones in the middle. That way you build a beam that is stronger per kilo than what nature supplied.
Glulam (glued laminated timber) consists of lamellas laid lengthwise on top of each other — that gives beams and girders for large spans. CLT (cross-laminated timber) has layers laid crosswise on top of each other, like plywood but tens of centimetres thick — that gives load-bearing walls and floor panels. Together they make tall timber buildings possible.
- Glulam
- lamellas lengthwise; beams and girders
- CLT
- crosswise; walls and floor panels
- Strength
- the weak spot sits in one layer out of many
- Span
- tens of metres without intermediate support
- High-rise
- timber towers of over eighty metres
- Shape
- curved beams are possible
Fair is fair: laminated timber is glued timber, and the glue is the point to watch. In a fire, glulam performs excellently — it chars on the outside and keeps its load-bearing capacity longer than unprotected steel — but the glue lines are where performance varies between manufacturers. For structural work, what counts is the producer's accreditation, not the material in general.
What is already being built with it
High-rise in timber
Residential towers of over eighty metres now stand in Norway, Austria and Canada. They are lighter than concrete, which allows smaller foundations, and construction time is shorter because elements are prefabricated.
Arch bridges
Laminated beams can be produced curved, something that is impossible with solid timber. That makes bridges with spans of tens of metres possible.
Sports halls and swimming pools
The classic use: large spans without columns, and wood does not rust in a chlorine-rich environment the way steel does.
Free-form roofs
Undulating and curved roofs are much easier to achieve with glulam than with steel or concrete.
A thick timber beam chars on the outside, and that charred layer insulates the core. As a result, the beam loses load-bearing capacity slowly and predictably. Unprotected steel, on the other hand, suddenly loses its strength at a few hundred degrees. Structural engineers therefore work with a charring rate — with glulam, that is a calculable quantity.
From board to beam
- 1 · GradingLamellas are machine-graded for strength. The strongest go to the outer layers, where the stress is highest.
- 2 · Finger jointingShort pieces are joined end to end with finger joints to reach full length. That creates beams far longer than any tree.
- 3 · Gluing and pressingThe lamellas are glued and pressed in a mould under pressure — straight or curved, depending on the design.
- 4 · FinishingPlaning, cutting to size and, if needed, a fire-retardant or moisture-resistant treatment.
Glulam and CLT belong to the same family as plywood and OSB: all engineered wood, where the properties of the end product are designed rather than grown.
Frequently asked questions about laminated timber
Why is laminated timber stronger than solid timber?
Because a weak spot such as a large knot sits in one layer out of many, whereas in a solid beam it determines the strength of the whole. In addition, the strongest lamellas can be deliberately placed at the top and bottom.
What is the difference between glulam and CLT?
In glulam, the lamellas lie lengthwise on top of each other — that gives beams and girders. In CLT they lie crosswise — that gives load-bearing walls and floor panels.
Is timber construction fire-safe?
A thick timber beam chars on the outside and that layer insulates the core, so the load-bearing capacity decreases slowly and predictably. Unprotected steel loses its strength much more abruptly.
How high can you build in timber?
Residential towers of over eighty metres now stand in Norway, Austria and Canada. The limit is still moving.
Laminated timber in perspective
Wood whose properties are designed rather than grown.
Have a question about your project? Just ask — we're happy to help.
Photos via Wikimedia Commons: End grain of laminated timber: glued lamellas with growth rings — メルビル (Wikimedia Commons), CC BY-SA 3.0 · Rivière Montmorency, Québec — Cephas, CC BY-SA 3.0 · Richmond Olympic Oval, Canada — Duncan Rawlinson, CC BY 2.0
The Wood Guide
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- Wood in modern architecture
- Technology and the future of wood
- The characteristics of wood
- How wood moves
- Durability classes of wood
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