By: Hettie Watkinson
Editor: Sarah Paterson
As the modern construction industry strives towards more sustainable and efficient construction, our choice of building materials has become critical to ensure truly successful projects.
Specifically, we have seen an increase in the application of mass timber. It’s high strength-to-weight ratio, reduced environmental impact and minimal limitation in production size make it an ideal method for modern construction projects. The three key types of mass timber are Cross Laminated Timber (CLT), Laminated Veneer Lumber (LVL) and Glue-laminated Timber (Glulam).
Cross Laminated Timber (CLT)
Pioneered and introduced to the market in the 1990s by the Swiss, CLT is essentially a mega-plywood made from layers of plantation timber of ‘lamellas’. The internal layers are glued together with the grain alternating at 90-degree angles, finished with exterior layers that run lengthways to ensure optimum strength. Whilst it is 20% lighter than concrete, the even distribution of strength in the wood provides immense structural durability, making CLT suitable for complete floors, walls and roofs.
CLT provides shorter construction times, less noise, waste and therefore less disruption to surrounding communities. High rises made using CLT – instead of traditional steel or concrete – can reduce the building’s carbon footprint by up to 75%. Providing a 10-30% cost saving in the long run.
Despite, the current low awareness, we are seeing some fantastic examples of CLT in application around Australia. Founded in 2010, wood-solution company XLAM has provided the CLT to allow for a $125m 10-storey building in Southbank. We will see a floor added every four days at the peak of construction. XLAM aim’s to ultimately produce enough CLT to build projects at this rate, each week.
Laminated Veneer Lumber (LVL)
LVL is an engineered wood product that is manufactured by bonding together rotary peeled or sliced thin wood veneers under heat and pressure, with the grain of each layer aligned in the same direction. Comparable to solid timber, concrete and steel, it is the strongest wood-based product relative to its density, and its high modulus of elasticity means it has limited movement upon the application of stress.
Today, it is used for permanent structural applications including beams, lintels, purlins, truss chords and formwork. An advantage is that it can be manufactured at almost any length and is only restricted by the capacity to transport to site. Whilst it has a low production cost, a high capital is required to set up production facilities.
Developed in the 1970s, we are now seeing LVL introduced to the Australian construction market on large scale projects. The Phoenix Apartments in North Western Sydney (built by Strongbuild) are 134 apartments using 4000 cubic metres of timber with LVL walls, a lift shaft and CLT flooring.
Similarly, Homebush adopted the use of 37m spans of LVL with bolt connectors in their Netball Central project that involved the construction of 5 netball courts, a show court, administration office and amenities.
Glue-Laminated Timber (Glulam)
Glulam is comprised of numerous layers of dimensioned lumber that is glued together using durable, moisture-resistant structural adhesives. Made up of smaller pieces of stress graded and seasoned timber known as laminates, it is considerably stronger than regular timber. This also means it is is far less prone to natural defects.
In Australia, it is often used for structural or decorative beams, and has a similar aesthetic and finish quality to LVL. However, whilst priced competitively with structural steel, Glulam is the most expensive of the three key types of engineered wood.
Recently, we saw a great example at RMIT University in their recent development of The Garden Building, that incorporated Glulam posts and beams to allow for open spaces rather than enclosed walls. Upon assessment, the project effectively disproved the common misconception that timber buildings have a greater fire risk than those constructed from concrete or steel. When exposed to fire, a thin layer of char is created, however the timber maintains its internal strength, thus making it remarkably resistant.
Photo Credit: Peter Bennetts, NMBW