CONCRETE

A 60-metre-wide warehouse built without internal supports and primarily from laminated timber may have given the construction industry pause to reconsider comparative concrete and steel dominated building practice.

Serving as the processing factory for Kanuka Engineered Wood Products in Irongate Road (Hastings), the warehouse is understood to be one of the largest clear span constructions in the country.

A collaborative effort of Kanuka owner, Peter Roil and Structural Concepts engineer, Garry Newton, stemming from an initial idea of architect, Steve McGavock, the Richard Kepka Builders’ erected warehouse boasts numerous innovations.

One of the most notable being the substitution of steel with 300 cubic metres of pinus radiata, which Mr Roil says delivers several benefits.

“The environmental issues of using wood as a construction material because of wood’s sustainable attributes are becoming more recognised,” he says.

“The wood used in the building was grown in the region and manufactured from a low grade knotty material.

“[As a consequence of using wood] fixings for purlins and gurts can be of the conventional timber-based type and secondary type services can be easily fixed to the timber structure i.e, ducting and power cables etc.

“Erection can be undertaken using conventional building techniques and carpentry personnel without involving specialist subcontractors.”

Integral to the warehouse’s design are its large roof trusses, which have had their bottom chords laminated with douglas fir to provide extra strength. Utilising trusses meant covering the necessary building width also required smaller pieces of timber.

In line with this theme, the purlin span in the roof framing was divided by an intermediate beam. The gravity load of the trusses also allowed for smaller columns of 575 millimetre width.

Another innovation was the use of about 300,000 nails and 500 steel plates over every connection, bar the brace bays, which achieved less slippage and reduced costs. Keeping metal components to a minimum is also understood to have maximised the building’s cost-effectiveness, sustainability and fire resistance, given steel tends to buckle in high temperatures as opposed to the charring of laminated wood.

Constructing the warehouse commenced with all truss components being cut to length at the factory and one side of the brackets being fixed to the top and bottom chords. The floor was placed before erection of the trusses to provide a platform for the builders to work on and the trusses were then assembled upright in two batches of five.

All of the roof beams and purlins were fixed on the ground, including ceiling beams and timber ceiling bracing, as was the steel strap bracing and the roofing netting.

Six cranes, ranging in capacity from 25 to 50 tonnes, were then used to forklift the five trusses on to the pre-assembled columns. These trusses, with associated roof beams and connecting cleats, weighed just over 49 tonnes. End walls and one side wall were then completed along with the infill central roof bay.

From the start of the onsite assembly process through to the completion of the timber work ready for cladding took 12 weeks for four carpenters and two labourers.

Completed in June this year, 12 months after the commencement of design, the warehouse was promptly recognised at the recent 2008 Timber Design Awards.

“The award was initiated by the Timber Design Society in conjunction with New Zealand Wood and was in the Commercial Engineering Excellence category,” continues Mr Roil.
“The description for the category was ‘for the innovative use of timber, resulting in a distinctive technical/structural impact on a commercial industrial or public building environment’.

“This is the first time our company has entered this type of competition and we are very proud of winning this award.”

A manufacturer of laminated product for the Australian market, H5 laminated posts for the New Zealand domestic industry, as well as lintels and garage door beams for the local pre-cut house market, Kanuka is optimistic this development will serve as a stimulus for future growth.

“The opportunities for our company come from the increased profile the award offers in the design and build of timber buildings.

“With the increasing awareness of environmental issues involving the use of sustainable products in the world around us, more people are becoming aware of the sustainable properties offered by using wood as a construction material.

“Kanuka Engineered Wood Products is positioning itself to provide solutions for these timber buildings.”

Richard Kepka Builders

by Iain MacIntyre