Glued laminated timber (glulam/BSH) is the primary structural solution for spans beyond the capability of solid sawn timber. This guide provides span tables, section sizing guidance, and specification requirements for architects and engineers working with structural timber on projects requiring spans of 6–30+ metres.
Glulam beams are manufactured to EN 14080 by bonding multiple layers of strength-graded softwood with structural adhesive under factory-controlled conditions. The result is an engineered timber product with superior strength, stiffness, and dimensional stability compared to solid timber.
Glulam Strength Classes Explained
EN 14080 defines glulam strength classes using the prefix "GL" followed by the characteristic bending strength:
| Class | Bending Strength (fm,g,k) | Stiffness (E0,g,mean) | Shear Strength (fv,g,k) | Density (ρg,k) |
|---|---|---|---|---|
| GL20h | 20 N/mm² | 10,400 N/mm² | 3.5 N/mm² | 340 kg/m³ |
| GL24h | 24 N/mm² | 11,600 N/mm² | 3.5 N/mm² | 365 kg/m³ |
| GL26h | 26 N/mm² | 12,100 N/mm² | 3.5 N/mm² | 385 kg/m³ |
| GL28h | 28 N/mm² | 12,600 N/mm² | 3.5 N/mm² | 390 kg/m³ |
| GL30h | 30 N/mm² | 13,600 N/mm² | 3.5 N/mm² | 390 kg/m³ |
| GL32h | 32 N/mm² | 14,200 N/mm² | 3.5 N/mm² | 400 kg/m³ |
GL24h is the standard specification for most residential and light commercial applications. GL28h is specified for primary beams in larger buildings. GL32h and above are reserved for long-span public buildings, sports halls, and bridges.
Span Tables: GL24h Beams
The following tables provide indicative maximum spans for simply-supported GL24h glulam beams under common loading conditions. All values assume:
- Simply supported (no continuity)
- Lateral restraint provided at supports and at regular intervals
- Service class 1 (internal, heated building)
- Span/depth ratio limited to L/300 for deflection
Roof Beams (1.5 kN/m² imposed + 1.0 kN/m² dead load, beam spacing 3.0m)
| Section (b × d mm) | Maximum Span | Self-weight (kg/m) |
|---|---|---|
| 100 × 240 | 5.2 m | 8.8 |
| 120 × 300 | 6.8 m | 13.1 |
| 140 × 360 | 8.2 m | 18.4 |
| 140 × 400 | 9.0 m | 20.4 |
| 160 × 450 | 10.5 m | 26.3 |
| 160 × 500 | 11.5 m | 29.2 |
| 180 × 560 | 13.0 m | 36.8 |
| 180 × 630 | 14.5 m | 41.4 |
| 200 × 720 | 16.5 m | 52.6 |
| 200 × 800 | 18.0 m | 58.4 |
Floor Beams (2.5 kN/m² imposed + 1.5 kN/m² dead load, beam spacing 3.6m)
| Section (b × d mm) | Maximum Span | Self-weight (kg/m) |
|---|---|---|
| 120 × 300 | 5.5 m | 13.1 |
| 140 × 360 | 6.8 m | 18.4 |
| 140 × 450 | 8.0 m | 23.0 |
| 160 × 500 | 9.5 m | 29.2 |
| 180 × 560 | 11.0 m | 36.8 |
| 180 × 630 | 12.5 m | 41.4 |
| 200 × 720 | 14.0 m | 52.6 |
| 200 × 900 | 17.0 m | 65.7 |
All values are indicative for preliminary sizing only. Final design must be verified by a structural engineer to EN 1995-1-1 (Eurocode 5).
Span Tables: GL28h and GL32h Beams
For higher-performance applications, GL28h and GL32h allow longer spans or smaller sections:
Comparative Spans (Roof Loading, 3.0m beam spacing)
| Section (b × d mm) | GL24h | GL28h | GL32h |
|---|---|---|---|
| 140 × 400 | 9.0 m | 9.8 m | 10.5 m |
| 160 × 500 | 11.5 m | 12.5 m | 13.5 m |
| 180 × 630 | 14.5 m | 15.8 m | 17.0 m |
| 200 × 800 | 18.0 m | 19.5 m | 21.0 m |
| 200 × 1000 | 22.0 m | 24.0 m | 26.0 m |
The premium for GL28h over GL24h is typically 8–12%. GL32h commands a 15–25% premium and requires longer lead times due to the higher-grade lamination timber required.
Section Sizing: Quick Reference
For preliminary design, use these rules of thumb:
Roof beams (light loading):
- Depth ≈ Span / 17 to Span / 20
- Width ≈ Depth / 3 to Depth / 4
Floor beams (domestic loading):
- Depth ≈ Span / 13 to Span / 16
- Width ≈ Depth / 3 to Depth / 4
Floor beams (commercial loading):
- Depth ≈ Span / 11 to Span / 14
- Width ≈ Depth / 2.5 to Depth / 3.5
Example: 10m span roof beam
- Depth = 10,000 / 18 ≈ 560mm
- Width = 560 / 3.5 ≈ 160mm
- Preliminary section: 160 × 560mm GL24h
Appearance Classes
Glulam appearance class determines the visual quality of the beam surface:
| Class | Surface Quality | Typical Application |
|---|---|---|
| Industrial (Industriequalität) | Knots, open joints, rough surface permitted | Concealed structure, temporary works |
| Standard (Gebrauchsqualität) | Minor defects permitted, planed surface | Semi-exposed, painted applications |
| Architectural (Sichtqualität) | Knot-free outer laminations, filled defects, sanded | Fully exposed architectural beams |
Specification tip: Architectural appearance class adds approximately 15–25% to the beam cost but is essential for any exposed application. Specify on drawings and in the specification clause to avoid disputes.
Curved and Tapered Glulam
One of glulam's unique advantages is the ability to manufacture curved and tapered profiles:
Minimum Bending Radii
| Lamination Thickness | Minimum Radius |
|---|---|
| 33mm | 5.0 m |
| 40mm | 8.0 m |
| 45mm | 10.0 m |
Curved glulam is manufactured by bending laminations over a jig during the gluing process. Tighter radii require thinner laminations, increasing manufacturing cost and lead time.
Tapered Beams
Tapered glulam beams (deeper at midspan, shallower at supports) optimise material use for simply-supported applications. The taper angle is typically limited to 10° to avoid excessive shear stress at the tapered end.
Connection Design for Glulam
Glulam connections require careful design to avoid splitting and ensure load transfer:
Common Connection Types
- Concealed steel plates: Slotted into the beam with dowels — clean architectural appearance
- Steel shoes/hangers: External brackets — visible but simple to install
- Glued-in steel rods: Highest capacity, completely hidden — requires factory installation
- Through-bolts with steel plates: Simple, high-capacity — visible bolt heads
Design Considerations
- Minimum end distance: 7d (where d = dowel diameter) for loaded end
- Minimum edge distance: 3d for unloaded edge
- Moisture class affects connection capacity (use stainless steel for service class 2/3)
- Fire design: connections typically require additional timber cover or intumescent protection
Procurement and Lead Times
| Product | Typical Lead Time | Notes |
|---|---|---|
| GL24h standard sections (stock) | 5–10 working days | Most common sizes held in stock |
| GL24h custom sections | 2–4 weeks | Non-standard width or depth |
| GL28h / GL32h | 3–6 weeks | Higher-grade laminations required |
| Curved beams | 6–10 weeks | Jig manufacture + curing time |
| Large sections (>800mm deep) | 4–8 weeks | Press capacity constraints |
PuurModulair supplies BSH glulam beams in GL24h through GL32h, with standard sections available within 5–10 working days across the European delivery network. Request a specification quote for your project.
Related Resources
- Structural Timber Specification Guide — parent pillar guide
- C24 vs C16 vs C30 Timber Grading — solid timber alternative
- BSH Glued Laminated Beams — product specification
- Glued Laminated Turned Logs — structural log elements