Glued Laminated Timber (GLT) Guide

Discrete Increments

The lamella build-up is discrete - section depth increases in fixed jumps equal to the lamella thickness, not continuously. A manufacturer using 35 mm lamellae produces sections at 105 mm (3 lamellae), 140 mm, 175 mm, 210 mm, and so on. This has direct implications for structural optimisation: the designer selects from available depth increments rather than specifying an arbitrary section depth. Elements specified outside of these discrete steps introduces additional machining, and cost.

Understanding the manufacturer's lamella increment is important for early structural sizing and for coordinating section depths with connection detailing, architectural clearances, and fire engineering (where charring calculations are sensitive to lamella thickness and glue line positions).

The European convention, typically European Spruce, uses a standard lamella thickness of approximately 40 mm. Australian manufacturers may use different lamella thicknesses reflecting local species, press equipment, and production standards. Hyne Timber and ASH (Australian Sustainable Hardwoods) are the primary Australian glulam producers, each with their own lamella dimensions and section profiles.

Typical Dimensional Ranges

Block-glued sections, where multiple standard-width members are bonded side by side, produce wider sections for heavy-duty beams, transfer structures, and bridge applications. The block-gluing process adds a manufacturing step and should be specified early.

Figure 2: Single GLT and Block Glued elements, showing different kinds of glue lines. Top: Buildups that make good use of fabrication limits. Bottom: Additional processing that doesn't meet well with fabrication limits. Note: Your fabrication limits may be different, always check with your fabrication team.
 

Long Span

Glulam's primary structural opportunity is long span. By building up section depth from multiple lamellae, glulam beams can span distances that solid timber cannot approach: 20 m, 30 m, and beyond for straight beams, with curved arches and portal frames achieving significantly greater spans.
This capability positions glulam as a direct alternative to steel and concrete for large-span structures: sports halls, performance venues, exhibition spaces, commercial roofs, airport terminals, and pedestrian and vehicular bridges. The strength-to-weight ratio of glulam is favourable, a glulam beam weighs significantly less than an equivalent steel or concrete member, which can translate to smaller foundations, lighter crane requirements, and reduced seismic forces.

Figure 3: A modern pedestrian bridge in Neckartenzlingen uses a gracefully curved glulam timber arch as its main span.

Figure 4: Sydney Fish Market beams during installation

Prefab Processing

Glulam members are routinely CNC-machined before dispatch. Connection slots, bolt holes, bearing rebates, notches, and surface profiles are cut with high precision, enabling complex connection geometries and tight tolerances that would be difficult or impossible to achieve with site-based cutting. This precision supports the prefabrication workflow that characterises modern mass timber construction and allows glulam to integrate seamlessly with CLT panels, steel connectors, and concrete elements in hybrid structures.

Three-Dimensional Form

Glulam's layered manufacturing process allows members to be curved during pressing. Lamellae are placed into a curved jig before the adhesive cures, producing a permanently curved element. This enables single-curvature forms (arches, portal frames, curved beams) and, with more advanced manufacturing, double-curvature forms (twisted or warped surfaces).

This is a distinctive capability. Few other timber, steel or concrete alternatives can achieve complex curved forms as efficiently as glulam. Projects like Bunjil Place in Melbourne demonstrate the architectural potential of curved glulam at building scale. The minimum curve radius is approximately 100 times the lamella thickness. Thinner lamellae enable tighter curves, this is one reason lamella thickness is a design consideration, not just a structural parameter.

Figure 5: Bunjil Place in Melbourne, dispalying a complex array of curved GLT elements

Natural Material and Biophilic Quality

Glulam is frequently specified as an expressed elements, serving both structural and architectural roles. The natural wood grain, warmth, and tactile quality of exposed glulam contribute to biophilic design outcomes: reduced occupant stress, improved comfort, and enhanced perceptions of interior quality.

Manufacturers offer glulam in different appearance grades. For expressed applications, high-quality surface finishes with minimal defects can be specified. For concealed applications (behind linings or cladding), lower appearance grades reduce cost without affecting structural performance.

Carbon Storage

Glulam stores atmospheric carbon captured during tree growth. Like CLT, a cubic metre of glulam typically stores more CO₂ than is emitted during its manufacture, transport, and installation. Environmental claims should be verified through product-specific Environmental Product Declarations (EPDs) and chain-of-custody certification (FSC or PEFC).
 

Species

Glulam is manufactured from both softwood and hardwood species. The species affects strength, stiffness, density, appearance, durability, and adhesive compatibility.

Softwood glulam is the most common globally. European spruce is the standard for imported glulam. Radiata Pine and other plantation softwoods are used for Australian-manufactured glulam. Softwood glulam offers good strength-to-weight ratio, consistent properties, and established design data.

Hardwood glulam offers higher density and strength, enhanced natural durability (reducing treatment requirements for exterior and high-exposure applications), and distinctive visual character. Australian Sustainable Hardwoods (ASH) produces hardwood glulam from Victorian Ash species. Hardwood glulam is particularly relevant for exterior structures, bridges, and applications requiring high natural durability or a specific aesthetic.

All species should be noted in the specification. Structural design properties differ between species and manufacturers.

Australian Projects

Glulam has a growing track record in Australian construction. Notable applications include commercial buildings in Sydney and Melbourne using glulam post-and-beam structures with CLT floors, pedestrian and vehicular bridges (where glulam's durability and long-span capability are demonstrated in exterior conditions), education and community buildings where expressed glulam beams and columns contribute to biophilic design quality, and heritage and cultural projects where glulam's natural material quality is valued.

Figure 6: Hines Collingwood in Melbourne, building on a growing line of succesful commercial timber offices in Australia
 

Glulam manufacturing is a controlled factory process with well-established quality assurance.

Production Sequence

The sequence for producing GLT is:

1. Timber reception and grading
   1. Incoming boards are machine stress graded and sorted
   2. Boards not meeting the required grade are rejected
2. Kiln drying
   1. Boards are dried to approximately 12% MC to ensure adhesive compatibility and dimensional stability
3. Finger jointing
   1. Shorter boards are joined end-to-end with structural finger joints, producing continuous lamellae of the required member length
4. Layup
   1. Lamellae are stacked face-to-face in the required section configuration
   2. In some instances, higher-grade lamellae are placed at the outer faces where bending stresses are highest. This makes better structural utilisation of the fibre.
5. Adhesive application and pressing
   1. Structural adhesive is applied between lamellae and the assembly is consolidated under hydraulic or mechanical pressure
   2. For curved members, the assembly is pressed in a curved jig
6. Curing
   1. The assembly is held under pressure until the adhesive reaches full cure strength, typically 6-16 hours at room temperature
7. Machining
   1. The cured member is machined to final dimensions including connection slots, bolt holes, bearing rebates, notches, and surface profiles.

Adhesive Systems

The two most common adhesive types in glulam manufacture are resorcinol-formaldehyde (RF) and melamine-urea-formaldehyde (MUF), both of which produce durable structural bonds suitable for exterior exposure. Polyurethane (PUR) adhesives are also used, particularly where a light-coloured or invisible glue line is desired for expressed applications. RF adhesives produce a dark glue line; MUF produces a lighter line; PUR is nearly invisible.

Adhesive selection affects appearance (critical for expressed members), moisture tolerance, fire behaviour at glue lines, and VOC emissions for indoor air quality.

Quality Assurance

Australian glulam manufacture is governed by AS/NZS 1328.1: Glued Laminated Structural Timber. The Glued Laminated Timber Association of Australia (GLTAA) operates an independently audited quality assurance program for its members, including regular independent testing. Products of GLTAA members carry the GLTAA quality mark.

Design Standards

Glulam structural design in Australia follows AS 1720.1: Timber Structures - Design Methods, using manufacturer-supplied characteristic values. AS/NZS 1328.1 specifies performance requirements for glulam members and quality control requirements for manufacturers.

Design properties are product-specific and vary between manufacturers, species, and grade combinations. Designers should use the manufacturer's published characteristic values - not generic glulam properties.

Key Design Considerations

Glulam design involves assessing:

• Bending capacity
  • Governed by the strength of outer lamellae and the section's effective depth
• Shear capacity
  • Governed by loads at supports and near concentrated loads
• Deflection
  • Often the governing criterion for long-span beams, both short and long term deflection
• Bearing
  • Governed by loads at supports and at concentrated loads 
  • Both parallel and perpendicular-to-grain bearing capacity, depending on load direction
• Lateral stability
  • Deep, slender beams and columns require lateral restraint to prevent buckling
• Connections
  • Glulam connection design follows the same principles as CLT: self-tapping screws, steel plates, knife plates, and bolted connections are all used; connection capacity depends on species, density, grain orientation, and edge distances of fasteners.

Vibration

Glulam floor beams supporting CLT or other floor panels should be checked for vibration under foot traffic, particularly in residential and commercial applications. The lighter weight of timber structures compared to concrete means natural frequency and acceleration response must be verified.

Glulam chars at a predictable rate in fire, the same mechanism as CLT. As the outer surface burns, the char layer insulates the timber beneath, maintaining the structural capacity of the residual section. The charring rate for glulam is typically 0.65–0.7 mm per minute for softwood species under standard fire exposure.

Fire Resistance Levels (FRLs) are achieved through oversized sections (designing the member with additional depth to account for expected char loss during the required fire resistance period) or encapsulation (protecting the member with fire-rated plasterboard linings).

Glulam's large section sizes provide inherent fire resistance. A deep glulam beam has more sacrificial timber available for charring than a steel beam has margin before reaching critical temperature. This does not make glulam superior to steel in fire — it means the fire behaviour is different, the failure mode is predictable, and the engineering methodology is well established.

Fire performance at connections requires particular attention. Steel connector plates, bolts, and brackets lose strength at elevated temperatures. Connection fire protection strategies include recessing steel behind timber, using timber plugs over bolt heads, and applying intumescent coatings. 

For detailed guidance, see WoodSolutions Technical Design Guide 17: Fire Safe Design of Timber Structures.
 

Glulam is manufactured at approximately 12% MC and is intended for dry service conditions (Service Class 1 or 2) in most structural applications. The moisture management principles are the same as for CLT - protect during transport and storage, limit construction-phase exposure, acclimatise before enclosure, and maintain the building envelope.

For exterior applications (bridges, canopies, exposed structures), glulam can be specified in Service Class 3 (exterior exposed) provided the correct species/adhesive combination is used and suitable protective design and maintenance measures are implemented. Hardwood species with natural durability Class 1 or 2 are typically specified for exterior glulam. Preservative treatment is an alternative for softwood species in exterior applications.

For detailed guidance moisture management, see Moisture Management in Mass Timber Construction, and Climate-Based Moisture Considerations for Timber Across Australia.