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Engineered Timber Processes

21 Mar 2018

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More than half of Australia's residents live in capital cities, and with the ABS predicting this percentage to rise to 72% by 2053, we'll need increase the density and liveability of our cities.

Key to our capacity to build for the future is a deep understanding of new building technologies - and the raw resources that we rely on to build our cities. Not only is it our shared responsibility to ensure the best application of building products for durability, cost-effectiveness and safety, but it's also our responsibility to make the best use of Australia's natural resources, and build with future generations in mind.

Along with a growing body of work supporting biophilic urbanism in Australia, recent changes to the National Construction Code have made both massive and lightweight timber multi-storey construction more accessible.

Before delving into the suitable applications and properties of engineered timber products, let's explore the basic methods that are used to manufacture timber.

CUTTING
Solid-Sawn Timber
Is made by cutting saw logs to achieve specific size, appearance and / or strength outcomes. Solid timber products are often 'seasoned' (kiln dried) to the correct moisture content for their intended use. By-products such as bark, woodchip and saw dust are used for landscaping, energy generation or other engineered timber products.
Where it's used: Framing, landscaping, flooring, furniture, pallets / packaging

GLT (Glue Laminated Timber)
Is made from gluing solid-sawn timber boards together adjacently. By gluing together smaller pieces of timber, the effect of defects (knots) and changes in density is offset. GLT can be used for longer spans and heavier loads than solid timber can, and is available with a curved, cambered or straight profile.
Where it's used: Roof trusses, posts / columns, beams, portal frames

CLT (Cross Laminated Timber)
Is made from gluing solid-sawn timber boards together in layers. Each layer is oriented perpendicular to the adjacent layers. Timber is known as an anisotropic material, so the structural capacity changes depending on the direction that the force is applied. By gluing the wood at perpendicular angles, CLT achieves structural rigidity in both directions.
Where it's used: Wall panels, cassette floors

PEELING
LVL (Laminated Veneer Lumber)
Is made from gluing layers of rotary peeled or sliced thin wood (veneers) together, with the grain aligning adjacently. By gluing veneers together, the effects of defects (knots) and changes in the density is offset. While LVL is comparable in strength to solid timber, its advantage is that it can be manufactured to almost any length. The high glue content in LVL also makes it less prone to shrinking and warping.
Where it's used: Headers, beams, rim boards, roof truss chords

Plywood
Is made from gluing together rotary peeled or sliced thin wood veneer (plies) together, with the grain of each layer oriented perpendicular to the adjacent layers. By alternating the grain the timber is less likely to split when nailed, and is also less likely to expand and shrink. It is difficult to bend plywood perpendicular to the grain.
Where it's used: Roofing, subfloors, wind bracing panels, decorative applications

CHIPPING, FLAKING & STRANDING
Particle Board
Is made from pressing and extruding a mixture of resin and wood chips or sawdust. Particle board is most beneficial when price is more important than strength. However, it is sensitive to moisture (swelling and/or discolouring easily), and typically should not be used outdoors or in environments with a high humidity level.
Where it's used: Floor underlay, bracing, furniture

OSB (Oriented Strand Board)
Is made from pressing and extruding a mixture of adhesives and wood strands in specific orientations. It differs from particle board in that the wood strands are much larger than wood chip (usually 2.5cm to 15cm long). OSB has a greater load-bearing capacity than particle board and is also more resistant to water.
Where it's used: Walls, flooring, roof decking