Explainer: A guide to cross laminated timber and more

Mass timber is currently one of the big trends sweeping through global construction. Here is a quick starter’s guide to laminated veneer lumber, glulam and cross-laminated timber.

Laminated Veneer Lumber

Laminated Veneer Lumber (LVL) has been in use in Australian construction since at least 1986.

That’s the year the first LVL beams rolled off the production lines at Carter Holt Harvey’s plant in South Australia. Production has since moved to New Zealand, where Radiata pine is sourced from FSC and PEFC-certified plantation forests.

Of the 100,000 cubic metres or so of LVL the company produces annually, around 80 per cent is sold into the Australian market.

What’s it used for?

LVL is generally used for structural applications including portal frames for warehouses; also joists, columns and bearers for residential, commercial and education projects, among others.

The Melbourne School of Design, for example, has LVL coffers in its roof supplied by CHH to Timberbuilt Solutions.

Is it a fire risk?

According to Michael Murphy, market manager LVL for the company, like any material, fire resistance comes down to the right material, the right design and the right detailing, including proper installation. Under these circumstances, in the event of a fire, an LVL portal frame is often left standing, while steel will have distorted, buckled and collapsed.

One of the ways in which fire safety can be delivered is oversizing the beams to increase the time factor before charring weakens the timber.

This addresses some of the requirements of the National Construction Code on sufficient time for safe egress of occupants.

How is it made?

LVL is manufactured by “peeling the logs” into 3.5mm veneers. These are then clipped into sheets measuring 1.3m by 2.5m. The ends are then profiled, the sheets are jointed together, glued and pressed. Veneers are staggered in the lay-up.

As it is a continuous production line, the only limit on the length of beams is the end-user’s transport solution.

The company has supplied some beams 27m long and 1200mm deep.

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The phenolic adhesive used is a structural adhesive. It does not give off formaldehyde, as while the VOC is part of the chemistry of the adhesive, when it is exposed to air it is “locked up” in the adhesive compound resulting in a product that emits zero VOCs.

It is one of the most inert glues around, Murphy says.

The use of the phenolic adhesive is required under the relevant Australian standards. There is also a good 70 to 80 years of gathered data on how it performs under a range of conditions.

Glulam

Glued laminated timber, or glulam, is used for both structural and architectural applications. The majority of glulam produced worldwide is manufactured from softwoods such as pine or spruce.

Australian Sustainable Hardwoods in Victoria, however, is manufacturing a glulam from 100 per cent Victorian ash regrowth.

Daniel Wright, ASH national marketing manager, says all the timber has chain of custody documentation, as well as either PEFC or AFS certification.

The company is also third-party certified to ISO 14001 for quality, environment and safety.

There are two main glulam products produced by its mill – an F17 beam that is similar to a typical hardwood structural beam and is suitable for exposed applications, and a higher load GL18 beam. They are used for parts of buildings including beams, joists, columns, studs and lintels.

For one recent project, the company supplied VicBeam and Timber Imagineering with 16m long beams measuring 400mm by 400mm in girth as posts for a new university building in Melbourne.

The plant has the capacity to produce beams as wide as 2metre x 2 metres.

How it is made

Manufacturing the glulam starts with offcuts from the company’s hardwood milling operations. These are finger jointed and then laminated together with glues using a $6.5 million automated production line.

The required length of the finished product is specified during production. Once it emerges from the laminating process, it is then pressed and stacked.

No waste

Wright says the company moved into glulam as it aims to ensure 100 per cent of any log is used, and that the value and yield of each stick of timber is maximised.

Even sawdust from its operations is used to provide energy for the timber drying kilns, something Wright says is saving the firm around $4 million a year on energy bills.

Glulam uses the “shorts” or “dregs” from milling regular sawn lumber and gives them a high-value use. As well as using its own shorts, the company purchases them from other mills.

How is quality ensured?

The company uses luminescence in the glue on both the finger jointing line and the laminating line. The glued elements pass under a black light so the quality of the glue application can be checked.

The glues are a polyurethane product that satisfies the requirements for an E0 rating in terms of VOC emissions.

The company has an on-site lab for testing its products, and its processes are also independently audited every few months.

Tests include a cleavage test, measurements of elasticity and rupture.

Is it a fire risk?

Even as a standard hardwood plant or beam, Victorian Ash is one of the species that is rated as having inherent fire resistance properties.

“Victorian Ash has historical data for fire performance, Wright says.

Exova Warrington has also carried out independent tests on its performance.

Independent tests are also being carried out for use of the product in high-rise applications.

An advantage over steel is that engineered timber is less of a thermal conductor. A steel staircase, for example, located above a fire will be potentially too hot to walk down and escape, Wright says.

An engineered timber wall, however, can have a fire on one side but the room on the other side and its occupants will not necessarily be feeling the heat because it is such a good insulator.

Cross Laminated Timber

Stora Enso is a European manufacturer of CLT. Australian projects it has supplied to include Lendlease’s International House and Library at the Dock.

It has been manufacturing CLT since 2008. The process of manufacturing involves glueing planks together into boards that are then laid one on top of the other at right angles and bonded with adhesive, then subjected to pressing.

The cross-angle lamination process gives the product greater structural strength along two axis, unlike a standard board.

The panels are fabricated with between three and eight layers, with the thicknesses ranging from 20mm to 40mm, depending on the requirements of the final application. They can be up to 16m long and 2.95m high, and design details such as penetrations for services, windows or doors can be prefabricated into the panels.

Erkki Valikangas, supply chain manager of engineered wood products at Stora Enso’s Australian office, says the timber used at its two CLT plants in Austria is 100 per cent PEFC-certified softwood timber from forests in Central Europe.

The two plants are located adjacent to sawmills to ensure an integrated supply chain.

Is formaldehyde an issue?

Valikangas says strict environmental policies the company has put in place include full traceability of every log used in CLT manufacture back to the original forest location.

The adhesives do not contain formaldehyde, and give off no VOC emissions. This is verified by the products’ Environmental Product Declarations.

How is the quality assured?

All the products are certified to European standards and have undergone an extensive testing regime under the formal European Technical Assessment regime to establish its technical and mechanical properties, Valikangas says.

Is it a fire risk?

It has also been extensively tested for fire, including the construction of significant structures that have been subjected to fire and an analysis carried out.

“Wood has a very predictable char rate of 0.65mm per minute,” Valikangas says.

“It is a question of education and understanding. If you think about it as little sticks in a camp fire, yes that burns. But we are talking massive timbers. And if you put a big log in a small fire, it will extinguish itself. It won’t burn.”

Easy win for passive house standards

The edge-glueing technique the company uses gives its products improved performance in terms of delivering airtight

construction, he says. The timber itself also has positive thermal qualities.

“With CLT you can easily achieve Passive House standard.”

The dimensional accuracy of the prefabrication of openings for windows and other inclusions also makes it straightforward to achieve better airtightness, he says.

Who’s using it?

The company’s products have been used in Europe for some very large projects including a wind turbine in Germany, multi-residential, commercial offices, public buildings and education buildings.

Valikangas says there is a strong market from schools and nurseries [child care].

These projects appreciate the biophilic qualities of the timber, and also the speed of construction.

“They build during the children’s holiday time,” he says. “They can quickly get most of the structure built, and that keeps everyone safer as there are no children near the site.”

The environmental credentials are another aspect, he says, as the educators want to “lead by example” in terms of helping children learn the importance of sustainability.