CLT takes timber structures to new heights

CLT was used in the construction of the new Hagley Backpackers in Christchurch.

CLT was used in the construction of the new Hagley Backpackers in Christchurch.

The development and introduction of cross-laminated timber (CLT) is causing a lot of excitement in the Australasian construction sector, says Jeff Parker, technical manager of the Wood Processors and Manufacturers Association.

“CLT is a structural product suitable for load-bearing construction including multi-storey buildings. It is effectively a wooden form of a concrete tilt slab, which has already been utilised for several exciting commercial projects on both sides of the Tasman.”

Jeff says CLT has numerous advantages over other construction materials.

“It is environmentally friendly and prefabricated to customers’ specifications including pre-cut openings for windows and doors, which makes it quick and easy to assemble. It is also strong, has excellent seismic resistance, and appears to cost around 10 to 15 percent less than concrete or steel equivalents.”

CLT panels have been produced in Europe for some time.

However they have only recently been introduced to New Zealand in recent years through Nelson firm XLam NZ Ltd, the only manufacturer of the product in the Southern Hemisphere.

XLam has developed design and construction methodologies for local conditions and has now supplied more than 200 CLT projects in New Zealand and Australia.

An Australian firm Hyne Timber, has become an equity partner in XLam, which now has an Australian sales and design office, with a 12,0002 manufacturing facility set to open in Wodonga, New South Wales in mid 2017.

In New Zealand the firm has already doubled its factory space to meet demand.

CLT is made of layers of solid timber, alternating grain direction at 90 degrees (whereas glue-laminated timber is layered with the grain). The grain of the exterior layers runs lengthways, providing optimum strength.

It can be produced with three, five or seven layers of different thicknesses with a range of strengths and physical characteristics suitable for a large variety of architectural and industrial uses.

Jeff says one of the main benefits of CLT is that when combined with other engineered wood products (EWP) such as LVL, plywood, glulam and light timber truss systems, it enables the economic construction of taller, multi-occupancy wooden buildings.

“That’s when these products really come into their own, particularly for large commercial buildings with big spans that need Glulam or LVL for long reach members, and utilise CLT for floors and walls. Architects and designers are starting to come up with all sorts of exciting combinations for these products which can prove more cost effective than some other conventional builds.”

The cost savings are often created by a combination of easier foundation work, rapid construction, and smaller work crews, with added benefits of using EWPs being improved thermal mass and insulation, increased sustainability and a ‘huge amount’ of carbon sequestered in the building.

CLT used to great effect inside the Hagley Backpackers building.

CLT used to great effect inside the Hagley Backpackers building.

The CLT system is also airtight, fire resistant, provides thermal and acoustic insulation and has no toxic elements, making assembly environmentally and health friendly, says Jeff.

“As a dry building system there is also a minimum of swelling and shrinkage of the elements.”

Commercial projects constructed using CLT include a 300 bed backpackers building in Bealey Avenue, Christchurch, which comprised around 540 cubic metres of CLT in the floors, walls and ceiling structure.

“This building was modeled in 3D on CAD/CAM software, with all panels CNC cut to millimetre precision. This allowed for a rapid build programme,” says Jeff.

In Melbourne a 32 metre, 10 storey apartment building was built in the Docklands area of the city in 2012-2013 utilising CLT, and has achieved an estimated reduction in CO2 equivalent emissions of more than 1,400 tonnes compared to concrete and steel.

The building, which had a timber volume of 1,010 cubic metres also requires less energy to heat and cool, creating significant energy cost savings.

CLT is also highly suitable for residential applications, with speed of erection a particular benefit.

A home built on a steep site in Nelson had its 100m2  XLam floor installed in one hour, the upper 100m2  floor in 1.5 hours, and 200m2  pitched roof in 2.5 hours.

It appears the sky is the limit for the future of engineered timber products in the commercial sphere.

In London researchers from the University of Cambridge and PLP Architecture have revealed a concept for the city’s first wooden skyscraper, a 300 metre tall, 80 storey building using the latest timber technologies. If realised, the building referred to as ‘The Toothpick’ would become the tallest wooden structure in the world and the city’s second tallest building after The Shard.

“The whole design envelope for wood structures has changed with the emergence of engineered wood products. It is exciting to see larger and taller wooden buildings being planned and built in Australasia and around the world, as well as the growing use of these technologies in the residential sector,” says Jeff.

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