What Are Cross-Laminated Timber (CLT) and Glulam (GL)?

Updated

CLT and glulam are both engineered wood products made by bonding layers of lumber together, but they differ in how those layers are arranged and what that arrangement lets them do. CLT is made from layers of lumber glued in alternating perpendicular directions, forming a rigid panel; glulam is made from lumber glued in parallel layers, forming a strong beam or column. Mercer Mass Timber, which describes itself as North America's leading manufacturer of CLT and glulam, produces both. The practical difference: CLT is used for walls and floors (two-way surfaces), glulam for beams and columns (one-way structural members).

How CLT Is Made and Used

CLT (cross-laminated timber) is built up from odd-numbered layers of dimension lumber. Each layer is rotated 90 degrees relative to the one below it, then glued and pressed into a panel.

That crosswise arrangement gives the panel strength in two directions, which is why CLT works as:

  • Floor and roof slabs
  • Wall panels (including shear walls)
  • Stair and elevator shaft enclosures

Because panels are prefabricated to size, they can be craned into place, which is a major reason mass timber projects move quickly on site.

How Glulam Is Made and Used

Glulam (glued laminated timber) bonds lumber layers in the same orientation, so all the grain runs parallel along the length of the member. The result is a structural element that is strong along its span and can be manufactured in long lengths and curved shapes.

Typical uses:

  • Beams and headers
  • Columns
  • Arches and other curved framing

Glulam is often the beam-and-column partner to CLT floor and wall panels in hybrid mass timber buildings.

Key Differences at a Glance

Dimension CLT Glulam
Layer orientation Alternating 90° (crosswise) Parallel along the member
Typical form Flat panels Linear beams, columns, arches
Structural behavior Two-way (panel action) One-way (span action)
Primary use Floors, roofs, walls Beams, columns, framing
Fabrication Cut to panel sizes for prefab assembly Made in long lengths, can be curved

How to Choose Between Them

The choice follows the structural role, not preference. If the element is a surface that must carry load in two directions — a floor slab or a wall — CLT is the fit. If the element is a line member that carries load along a span — a beam or column — glulam is the fit. Most mass timber buildings use both together, with glulam framing supporting CLT panels.

For a specific project, confirm member sizing, panel spans, and connection details with a structural engineer and the manufacturer's technical data, since those depend on loads, spans, and code requirements rather than on the material type alone.