Glued laminated timber (glulam)

Dried, planed laminations with defects removed are glued together face to face under pressure, with the grain in the same direction. Timber defects such as knots do not end up in the same cross-section. This is the lamination effect: glulam has a higher average strength and a lower scatter than solid timber.

How is it made?

The laminations are dried and planed, defective sections are cut out, and the laminations are finger-jointed to the required length. A lamination is usually 45 mm thick for straight members and 33 mm for curved ones; radii below 7 m need even thinner laminations. Today the adhesive is almost exclusively light-coloured MUF; the older PRF produced a dark, reddish-brown glue line.

In the "c" (combined) classes, the stronger laminations are placed in the most highly stressed outer zones; in the "h" (homogeneous) classes all laminations are the same. The curved glued beam is not a new invention: Otto Hetzer received a patent for it in 1906.

Roofs of halls, swimming pools and factories

Glulam is the classic material for large, column-free spaces: the roofs of sports halls, swimming pools, factories, warehouses and showrooms. With a low self-weight and slender cross-sections, it spans large distances, and its shape can be freely designed: straight, pitched, curved and truss beams are all possible.

In swimming pools there is an added advantage: unlike steel, timber is not attacked by chlorinated air and does not corrode. The condition is properly designed ventilation and humidity control that keeps the indoor climate constant.

Technical data

Build-up

finger-jointed laminations glued in one direction; laminations 45 mm for straight members, 33 mm for curved ones

Raw material

usually spruce; also pine, larch and Douglas fir

Strength

standard classes GL24c, GL24h, GL28c, GL32c (bending strength 24–32 N/mm²); without designation GL24c

Density

depends on the species – spruce 440–470 kg/m³

Adhesive

today almost exclusively MUF (approx. 8.8 kg/m³)

Common sizes

stock members 60–200 mm wide and 100–400 mm deep; custom-made up to 2 m deep and 50 m long, straight or curved

Standard

EN 14080

What is it for?

large-span beams, columns, frames, arches

Applications

• straight beams on columns: 10–30 m span
• three-hinged arches: 20–60 m; trusses: 30–85 m
• columns, frames, cambered and curved beams – also to support CLT floors

Examples

• Gödöllő (Hungary), municipal swimming pool (2020). One of the largest glulam domes in Hungary: it consists of 42 ribs 22–30 m long, the eight main ribs with a cross-section of 140 × 18 cm. The dome spans more than 60 m, has an internal height of 24 m and a fire resistance of 60 minutes. Source
• Darmstadt (Germany), Nordbad (2022). Swimming pool with 1830 m² of water surface: the roof consists of glulam beams up to 30 m long and CLT elements, with an unsupported span of about 15 m over the teaching pool. Source
• Langenthal (Switzerland), production hall (2003). Two-hinged glulam arch (180 × 660 mm) with a glulam tie (180 × 260 mm): it spans 30 m without columns, with frames every 5.62 m. Source
• Gödöllő (Hungary), office building and showroom (2022–23). 310 m³ of glulam beams in the roof work together with 232 m³ of CLT in the floors – we managed the construction of the timber structure. Source

What to watch out for

• Glulam must be protected from persistent moisture, rain and sunlight; untreated outdoors, it turns grey over time.
• Glulam made with type I adhesive (EN 301) can be used in all three Eurocode 5 service classes, with type II only in protected places (classes 1 and 2).
• In dry conditions, chemical timber protection is not needed; the industry association does not even recommend chemical treatment for glulam.
• Homogeneous glulam stronger than GL24 is more expensive and takes longer to produce – for higher strength, the combined (c) classes are the economical choice.
• The maximum size is limited by transport and the production plant – for large members this must be clarified at the start of the design.
• Where exposed to the weather (use class 3.1 under the German DIN 68800), it may only be made from Douglas fir or larch heartwood, with laminations no thicker than 35 mm.