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Home , Timber framing

FEATURE Materials performance SECTION

Timber takes on new forms

While timber is a traditional material for New Zealand housing, it is still evolving. Engineered products are being used not only for aesthetics but also for their seismic strength in multi-level construction.

BY JEFF PARKER, TECHNICAL MANAGER, WOOD PROCESSORS AND MANUFACTURERS ASSOCIATION OF NEW ZEALAND

smaller dimension sawn timber through to laminated veneer (LVL) and I beams, glue laminated (glulam) timber and cross- laminated timber (CLT). Sawn sizes of structural timber are increas- ingly used in complex layouts. This is because advanced software, the increased reli- ability of graded structural timber and the ability to place LVL components in highly loaded areas COURTESY OF WOODFORM COURTESY – has extended options for building designers.

Curved 215 mm timber weatherboards provide new design opportunities. Overseas, for example, in , applied research into fire-resistant systems has allowed PHOTOGRAPH the use of light timber- systems to TIMBER AND WOOD is widely used in New new product is the curved 215 mm timber be extended to 6-storey . Work is Zealand construction. There are conventional weatherboard manufactured by Woodform. progressing on this front in both Australia and elements for structural and non-structural use, CodeMark approval has also been gained New Zealand. but innovative new products are emerging. for weatherboards that have been heat treated rather than more common treatment processes changing the game Advances in weatherboards involving infusion of anti-decay chemicals. Above the light timber-frame systems come Several producers have developed and heavy engineered wood components such as obtained CodeMark approval for conven- Most wood in structural elements LVL and glulam. Separately or together, these tional weatherboard systems with improved Structural products are the largest users materials are extending timber construction detailing and fixing systems. One interesting of wood in buildings. These range from into areas where it has not competed before.

50 — August/September 2015 — Build 149 Materials performance FEATURE SECTION COURTESY OF NELSON OF NELSON COURTESY – COURTESY OF TIMBERLAB SOLUTIONS COURTESY – PHOTOGRAPH PHOTOGRAPH

CNC machinery enables manufacture of 30 m long engineered wood products. Kaikoura District Council building – a world-first amalgam of CLT and LVL.

Glulam comprises layers of sawn timber structures such as foundations and connec- The Expan range includes , usually face bonded into beams of larger sizes tions can be smaller. In New Zealand, Nelson and floor systems. The prefabricated than can be obtained by other methods. Pine, Carter Holt Harvey and Juken New technology embeds -tensioned steel The utility of glulam, LVL and CLT has been Zealand manufacture LVL. tendons into timber to lock the system extended by the large investments made in together. The result is buildings that will CNC (computer ) machinery. Cross-laminated timber new addition move predictably in an earthquake but These will , rout, bore and the CLT is the latest addition to the engineered sustain no permanent damage. timber products into components ready to wood construction armoury. While it has be lifted, placed and fixed on site. been used in for some time, a New World first in Kaikoura One CNC machine, for example, enables Zealand factory – XLam in Nelson – is now The new Kaikoura District Council building is the processing of glulam, LVL, CLT and solid producing CLT panels and has developed an example of an Expan building. This post timber elements up to 30 m long, 4 m wide design and construction methodologies for and gravity structure is made of LVL, and 600 mm deep. local conditions. while the , or the lateral structure, are The speed and accuracy of this process The structural properties of CLT mean that CLT and LVL. They are post-tensioned to create significantly decreases construction time the design envelope for wood structures has rocking shear walls. and the time required on site for heavy-lifting changed, and worldwide, larger and taller This project is the first time globally that a machinery. This makes the production of structures are being built. A recent example CLT and LVL combination has been used to extremely complex structures significantly is a 10-storey CLT apartment building in make shear walls. The walls are 70% CLT and more cost effective. Melbourne. 30% LVL. The LVL is significantly stronger In Christchurch, a 300-bed backpackers and was added to areas of maximum stress to LVL a mature product building under construction has CLT floors, provide added strength. These are at each end LVL is a mature engineered wood product walls and ceiling – approximately 5,500 m2 of of the walls and within the core of the walls in New Zealand, and engineers and archi- CLT in total. The building was modelled in 3D where the largest post-tensioning stress occurs. tects are now learning how to best use its on CAD/CAM software, and all panels were A Potius stressed skin panel flooring system, structural and aesthetic properties. CNC cut to millimetre precision, allowing for fabricated using LVL, creates diaphragms It can be manufactured to required strength, a rapid build. between the shear walls distributing lateral stiffness, shear, bearing and connector prop- loads. Unlike most commercial buildings, erties. This means LVL components can be LVL and CLT in Expan buildings there is no concrete in the flooring systems. manufactured for a particular job at optimum All these technologies can come together in Potius roofing panels made from a similar performance, costs and use of resource. Expan timber buildings. Expan was researched­ system are preinsulated with polyurethane The very high strength to weight ratio and developed by a consortium at the Univer­ spray foam, and a preprimed MDF surface means loads are lower and therefore other sity of Canterbury School of Engineering. provides the ceiling lining.

Build 149 — August/September 2015 — 51