Glulam, or glued laminated timber, explained: how it's graded in Australia, where it works, how it performs, and how it’s produced.
Glulam is the engineered timber that does the work of a steel beam. Short lengths of graded, kiln-dried timber are finger-jointed end to end, stacked in horizontal layers and bonded under pressure into a single structural member – a beam, a column, a portal frame, an arch. Because the member is built up from short, small-dimension sections rather than cut from a large one, glulam makes structural use of timber a single solid beam couldn’t, and it reaches spans solid sawn timber can’t. It can also be left exposed as the finished surface.
Where cross-laminated timber is a panel – a floor plate, a wall – glulam is a linear member. The two are often specified in the same building and confused in the same breath, but they solve different problems: CLT makes surfaces, glulam makes the beams and columns those surfaces rest on. Both sit within the broader family of engineered mass timber.
What it's made from
The laminations can be curved during pressing, which is why glulam appears as arches and cambered beams sawn timber could never form. The timber itself varies by region: jarrah in the west; Tasmanian oak and radiata pine through the south-east; spotted gum, slash pine, blackbutt and ironbark in the north-east. The laminations are held together with a structural adhesive, which is the fact that makes glulam an engineered rather than a natural product in the purist sense.
How it's graded and what to specify
In Australia, glulam is manufactured to the product standard AS/NZS 1328.1 and designed to AS 1720.1. It’s branded with a GL grade – GL8, GL10, GL12, GL13, GL17 or GL18 – with the number tracking the timber’s stiffness. The grade is a performance target assessed against a standard beam depth of 300 millimetres, and independent of the species or mill it came from. On a drawing it appears as, for instance, 315×85 GL18, with an S for a straight beam or a C for cambered.
One thing worth noting. The European standard uses the same “GL” prefix on a different scale – EN grades run GL20 to GL32 and describe bending strength, not stiffness – so an imported GL24 is not a stronger version of an Australian GL18; it’s a different measurement. To meet the National Construction Code directly the product needs to conform to AS/NZS 1328.1, and glulam graded to another standard can still be used but requires additional evidence of suitability before a certifier signs off.
Where glulam works best
Glulam earns its place where a building needs long clear spans, exposed structure, or shapes steel would make heavy and cold. At the Apple House, an education building by Okra, a sequence of spruce glulam portal frames forms the entire structure, with hempcrete cast between the frames to stiffen them and birch ply bracing the whole as a stressed skin. In the adaptive reuse of an 18th-century farmhouse at La Crêta by Bard Yersin, glulam beams carry the roof over a double-height volume reopened by cutting through a later concrete slab. It’s also lighter than the equivalent in steel – the industry association puts a structural timber member at around 60 per cent the weight of a comparable steel one – and more dimensionally stable than solid timber, less prone to warp, twist and shrink.
How it behaves in fire
Timber’s behaviour in fire is more predictable than its combustibility suggests. A large glulam section chars at a steady, measured rate – around 0.7 millimetres a minute for spruce-pine glulam under a standard fire, within the range the Australian and European standards assume, with the Australian provisions erring conservative. A recent review across species settled on 0.65 millimetres a minute as a reasonable figure for glulam and CLT for up to three hours, with denser timber charring more slowly. The char layer that forms insulates the timber beneath it, so the core stays cool and keeps carrying load – the basis of the equations used to predict fire endurance. Fire design under AS 1720.4 uses exactly this, sizing a member with a sacrificial depth of timber allowed to char away while the section beneath still performs. The vulnerability isn’t the large exposed member; it’s the connections and the smaller sections, which is where timber fire engineering does its careful work.
The carbon calculation
This is where the material is most oversold, and where the honest account is the more useful one. Timber stores carbon drawn down as the tree grows, and glulam’s manufacturing emissions are low next to steel’s or cement’s. Whether a glulam member’s whole-life carbon actually beats a steel one, though, depends on assumptions still under dispute. A University of Bath study comparing glulam with functionally equivalent steel found the result swung on three things: the end-of-life scenario, how the biogenic carbon is counted, and whether the timing of emissions is considered. Glulam came out lowest when incinerated with energy recovery; when recycling was modelled to current standards, its global warming potential landed among the steel options, with no clear ranking between the materials. Landfilled glulam beat steel only if its stored carbon was assumed to stay put permanently – an assumption the current construction-LCA standard, EN 15804:2019, doesn’t allow.
Australian modelling of mid-rise buildings tells the same story in ranges. Mass timber runs from 196 to 590 kilograms of CO2-e per square metre, post-tensioned concrete from 307 to 618. Timber’s average is lower, but the ranges overlap, and a poorly handled timber building can carry more embodied carbon than a well-handled concrete one. A review across studies puts the reduction against concrete and steel anywhere from 28 to 70 per cent, and the stored carbon only counts if the timber comes from genuinely well-managed forest – the kind of claim third-party certification exists to verify – and stays in service for decades. The honest figure for any given project is that it depends on how the building is built and what happens to it afterwards.
What are the trade offs with glulam?
Glulam isn’t inherently weatherproof. Exposed to weather or used in ground contact it needs the right adhesive and preservative treatment – Australian producers supply it treated to defined hazard classes – and detailing that keeps water off the end grain. It usually costs more per member than sawn timber, and its cost against steel is project-specific. And as the carbon accounting shows, its end-of-life pathway is part of its environmental case, not an afterthought.
Who's doing it well in Australia
The Glued Laminated Timber Association of Australia, formed in 1990, runs the quality-assurance scheme most reputable structural producers manufacture under, audited by an independent inspectorate; its members list is the practical starting point for sourcing an accredited product. WoodSolutions publishes the technical design guidance. Among Australian producers, Australian Sustainable Hardwoods makes a structural glulam, MASSLAM, rated to GL18 under the local standard.
Glulam isn’t so much the answer to a structural problem as a particular answer with particular conditions. It spans and shapes in ways solid timber can’t, it can be left as finished surface, and it can carry a lower carbon load than steel or concrete – when it’s specified from accredited stock, detailed to stay dry, and kept in service long enough for the stored carbon to mean something. Specified carelessly, it’s an expensive beam with a glue line. The difference is in the specification, which is the part worth getting right.
1. Review of the charring rates of different timber species, Fire and Materials (2024) | Fire and Materials
2. Experimental and reliability assessment of the charring rates of spruce-pine GLT beams, Resilient Cities and Structures (2025) | Resilient Cities and Structures
3. Australian mid-rise mass-timber vs post-tensioned concrete Monte Carlo LCA study (2021) | Building and Environment
4. Life Cycle Assessment with Carbon Footprint Analysis in Glulam Buildings: A Review, Buildings, MDPI (2025) | Buildings
