What glulam is
Glued laminated timber — glulam, in the German trade often simply called Leimbinder — is made from strength-graded laminations no more than 45 mm thick, bonded parallel to the grain into a beam. The decisive point: the section no longer grows in the forest, it is created in the press. Dimensions are therefore limited only by manufacture and transport.
Because the timber is broken down into laminations before bonding, knots and defects are distributed across the whole section instead of accumulating in one place. That makes glulam more homogeneous and more capable than grown solid timber of the same dimension.
Duo and trio beams
Beam laminated timber is the smaller sibling of glulam: two or three planks or squared sections bonded together — hence duo and trio. It is used wherever greater dimensional stability or larger sections are needed than KVH allows, without requiring a full glulam beam. Floor joists are the typical case.
Advantages
- Section and length freely selectable. The trunk is no longer the limit — it goes as far as the beam can still be transported.
- Very high capacity at low weight. For long-span roofs there is hardly a better ratio.
- Dimensionally stable. The laminations are bonded dry; the finished component barely moves.
- Curved and cambered shapes possible. Pitched beams, arches, variable depths — no solid timber can do that.
- More homogeneous than solid timber, because defects are spread across the section.
- Predictable fire behaviour. Large timber sections char slowly and evenly; residual capacity can be calculated.
- Visual grades available — glulam is often deliberately left exposed.
- Lower risk of insect attack than solid timber. Laminations are kiln dried to 12–15 per cent and graded, and susceptible zones are removed during manufacture. Should attack occur, glue lines and the homogenised section slow its spread — in solid timber damage can run unchecked along the sapwood zone through the whole member.
Drawbacks
- Considerably more expensive than solid timber. Grading, drying, planing, bonding and pressing all cost.
- Adhesive in the component. Relevant for clean separation at end of life and strict building-biology requirements.
- Lead time. Special sections and curved beams are manufactured, not taken from stock.
- Transport and erection. Large beams need special transport, a crane and space on site.
- No changes afterwards. Once pressed, a beam cannot be lengthened or reshaped.
- Glue lines dislike permanent moisture. The bond must match the service class; used wrongly, the glue line becomes the weak point.
- Tension perpendicular to the grain is the sensitive spot. At supports, notches, openings, connection details and in curved members, tensile stresses arise across the grain. Because timber is weakest there, cracking and brittle failure are a real risk — shrinkage and swelling add to it.
- Recurring inspection duty. Long spans bring a permanent obligation. More on that below.
What comes after construction
This is readily overlooked at design stage: the owner is legally obliged to ensure structural safety across the whole service life. For long-span structures that is no formality.
Buildings with spans over 12 m or cantilevers over 6 m fall into consequence class CC2 — sports halls, production halls, retail, riding arenas. A three-stage approach is recommended:
- Walk-through annually — visual check by the owner
- Inspection every 4 to 5 years — close-range examination by a qualified person
- Detailed examination every 12 to 15 years — by a specially qualified person, with material testing where required
The focus is on deformation and misalignment, cracking, moisture ingress from leaking roofs or blocked drainage, pest attack and the condition of the glue lines. Particular attention goes to halls with moisture input or fluctuating climate — riding arenas with damp footing, ice rinks, composting facilities.
A building logbook recording construction drawings, material grades, adhesive type, design loads and all later changes makes every one of these inspections easier and cheaper. Starting one at construction costs almost nothing; reconstructing it later is expensive.
Existing buildings: the adhesive
Until 2006, urea-formaldehyde adhesives were also used for load-bearing timber components. They were then excluded by building authorities as a precaution, because their application range is climatically limited. That does not mean every older hall has a problem — with properly made thin glue lines and no elevated moisture exposure there is normally no risk. At the first inspection of a bonded structure, however, the adhesive type should be determined in a laboratory; visual assessment is not reliable.
Cyclic loads: fatigue
Repeated loading can create micro-damage that grows over the years. Static design is then no longer sufficient and a fatigue verification is required. In practice this mainly affects timber road bridges and bell frames, plus floors under machinery with out-of-balance forces and structures under crane runways. For ordinary hall construction it is not an issue — but where one of those loads is present, it belongs in the design from the start.
Applications
- Hall construction: long-span roof beams without intermediate columns
- Downstand and upstand beams where solid timber no longer suffices
- Columns in skeleton and portal frames
- Exposed structures in halls, sports halls, schools and churches
- Floor joists with increased dimensional stability — usually as duo or trio beams
- Trimmers and ring beams in timber frame construction
- Bridges and outdoor structures, with bonding matched to the service class
Where to avoid glulam
- Standard roof sections. What KVH can do, KVH should do — glulam is simply too expensive there.
- Permanently damp conditions without suitable bonding. The glue line is the most sensitive part of the component.
- Planar components. Where a load-bearing wall or floor diaphragm is needed, cross-laminated timber is the right product.
- Sites without crane access. A 14-metre beam that cannot reach its destination helps nobody.
- Projects with unfinished design. Later dimensional changes to manufactured beams are expensive.
- Short-notice requirements. Special dimensions need lead time.