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The case for wooden buildings – and skyscrapers

There is an alternative to the concrete jungle—a renewable, flexible, light, strong and cost-effective building material that does grow on trees.

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The first application of the Pres-Lam construction system, the Nelson–Marlborough Institute of Technology (NMIT) Arts and Media Building

There is an alternative to the concrete jungle—a renewable, flexible, light, strong and cost-effective building material that does grow on trees

The world’s tallest building is the Burj Khalifia in Dubai, which opened at the start of the year. Looking from certain angles like an 828-metre-high pile of coins, it’s a delicate needle of steel, glass and concrete. Lots of concrete: something like 230,000 cubic metres of the stuff.

Concrete is used in incomprehensibly large quantities around the world every year. And making cement—the binding agent that holds sand and all the other aggregates together in a hard, stone-like mass—is a filthy business. For every tonne of cement produced, 1.25 tonnes of carbon dioxide are released into the atmosphere. The world’s cement plants account for five percent of global CO2 emissions. To make matters worse, concrete can’t be recycled so every new building needs new cement. There just doesn’t seem to be any alternative. But according to Andy Buchanan there is, and it’s close to hand.

On the face of it, the idea of building something like the Burj Khalifia—or any other high- or even medium-rise building—from wood is laughable. The tallest wooden structure, the Mühlacker radio tower built in Germany in the ‘30s, was 190 metres. But Professor Buchanan, who heads the University of Canterbury’s Department of Civil and Natural Resources Engineering, is entirely serious about using timber as an alternative to concrete and steel in heavy construction.

The best eco-credentials in the world are of precious little use if the construction industry, notoriously conservative about embracing new ways, doesn’t pick up on the technology

Previous attempts to create sizable timber framing have foundered because no one could figure out how to join together large pieces of timber. But the Pres-Lam system developed by Buchanan’s team of civil engineering researchers uses flexible steel couplings and embedded wire ropes to lace laminated wooden beams and columns into light but immensely strong structures.

And very resilient ones. Conventional steel and concrete framed buildings, provided they meet modern building codes, will not collapse in an earthquake. But their relative rigidity means that that they may be damaged—and they’re very expensive and time-consuming to fix. Because its joints can bend and its tendons stretch, Pres-Lam timber framing will move in an earthquake or a high wind then spring back into shape. If sections of a beam or column are damaged in the process, they can be unthreaded and replaced with comparative ease.

The whole concept is perfectly attuned to the zeitgeist. Wood is the only building material we can grow more of. And as they grow, trees eat CO2 and lock it away in their timbers. Manufacturing building materials from timber requires far less energy, and hence CO2 emissions, than it does to build with steel or concrete.

Pres-Lam construction system

Besides the durability of its construction materials and its reparability, the lifetime of a building is determined by the adaptability of its design and ease of renovation. When a structure can no longer economically serve an important function, the demolition ball starts to swing. The ability to couple and uncouple the beams and columns of a Pres-Lam building means it can be modified to suit changing needs, thereby extending its life.

And when its time comes, a Pres-Lam building could be easily disassembled and its beams and columns reused in another construction. Or they could be burned to generate electricity. One of the best ways to reduce CO2 emissions would be to use less fossil fuel and more renewable energy. Wood is stored solar energy. Cleanly burning the waste produced during the manufacture of wooden building components and burning these components at the end of their life would be a pretty good way to go about reducing emissions, Buchanan says.

But the best eco-credentials in the world are of precious little use if the construction industry, notoriously conservative about embracing new ways, doesn’t pick up on the technology. According to Buchanan, there are a lot of very good reasons why it should—starting with the bottom line. Sheer buildability is the system’s ace-in-the-hole. A laminated wooden beam or column weighs about half a tonne per cubic metres—about one fifth the weight of their concrete equivalents. Lightness allows for the use of larger pre-fabricated sub-assemblies, much easier transportation of components, smaller cranes on site and less expensive foundations on difficult sites. Using lighter wooden beams allows buildings to be designed with large internal spaces and fewer internal supports. Given excellent design and extensive prefabrication of components, Pres-Lam buildings are potentially faster and less expensive to build than conventional steel and concrete designs, Buchanan says.

Part of the R&D involved in developing the system required building a two-storey test building. As far as possible, commercial contractors were used for the supply of material, the fabrication of components and the actual construction itself. Construction took far less time than anticipated and a comparison of predicted and actual costs of the materials and fabrication suggests the building system will be competitive with conventional building systems. Researchers also created virtual design alternatives for several existing steel and concrete buildings.

The world’s urban population is projected to swell by two billion people by mid-century. Providing affordable housing is a challenge faced by cities the world over

Buchanan says a number of factors besides the obvious ecological and economic ones will drive demand for wooden buildings. The world’s urban population is projected to swell by two billion people by mid-century. Providing affordable housing is a challenge faced by cities the world over. Three- to five-storey wood-framed buildings offer economical housing through fast construction speed and low material costs, he says.

The Pres-Lam solution seems particularly suited to solving accommodation problems in the many cities in the developing world that are built on or near major fault lines. In these cities, the number of inhabitants has swelled far faster than the capacity to house them safely and tens of thousands of buildings have been erected in a haphazard, uninspected rush. An estimated 230,000 people died in the Haiti earthquake. That tragedy is almost certain to be surpassed when a major quake hits Karachi, Kathmandu, Lima or one of the others on the long list of big, poor cities facing inevitable major earthquakes. In Tehran, a quake of similar intensity to the Haiti event could kill one million people. (Some Iranian geologists have pressed their government for decades to move the capital because of the nexus of surrounding geologic faults.) Easily assembled quake-resistant mulltistorey buildings may be at least part of the answer to the problem.

While history suggests wood-framed buildings perform well in earthquakes, there have been no recent seismic events to gauge the performance of the few modern multistorey wooden buildings to have been built. But some of the uncertainty about the seismic performance of timber-framed buildings was dispelled in July last year when a seven-storey, wood-framed condo tower survived a 40-second shaking by a 7.5-magnitude earthquake on the world’s largest earthquake simulator in Miki City, Japan.

One major obstacle proponents of wooden buildings will have to overcome is the perception that wooden buildings are especially susceptible to fire. In many parts of the world, legislation limits the building of wood-frame structures to four storeys or less, but innovations in fire safety and advances in timber science mean many fire safety codes are now out of date. It’s a problem that has been recognised for a while. An APEC Business Advisory Council study in 2002 estimated that the opportunity costs from excessively prescriptive provisions on fire safety in building codes to suppliers and consumers of wood products in APEC economies was about US$10.8 billion a year. Some view outdated codes as nothing less than an unreasonable technical barrier to trade.

Some of the uncertainty about timber framed buildings was dispelled when a seven-storey, wood-framed condo tower survived a 40-second shaking by a 7.5-magnitude earthquake on the world’s largest earthquake simulator in Japan

But times are changing. Wood-framed buildings are going higher in North America, Japan and especially in Europe. Early last year, what is billed as the tallest timber residential building in the world was completed in Hackney, London. Built entirely of timber, the 30-metre, nine-storey building houses 29 apartments. The Norwegian Barents Secretariat has commissioned a 17-storey wooden building in Kirkenes, Norway, which will be used as a cultural centre.

New Zealand should be positioning itself to capitalise on the trend, says Buchanan. The way he sees it, we could grow the trees, produce the timber and fabricate the components. We could take orders for whole buildings over the internet and ship them out as bundles of precisely engineered laminates ready for assembly. “When we’re exporting logs we’re exporting jobs, sunshine … and all that should stay in New Zealand.”

It’s an attractive vision and one that has struck a chord with government. In May 2008, the Foundation for Research, Science and Technology approved $10 million funding to establish the Structural Timber Innovation Company (STIC). The government chipped in with funding for five years, matching the $5 million industry investment by Carter Holt Harvey, Nelson Pine Industries, Westbeam, Forest and Wood Products Australia, the Pine Manufacturers Association and Building Research. Besides the work being done at Canterbury, STIC will contract research from the University of Auckland, Sydney’s University of Technology, universities in Italy and elsewhere, and with BRANZ in Wellington. The initial aim of the company is to develop modular systems to build large-span multistorey buildings with adaptable open-plan interiors and very large span roof systems for single-storey timber buildings.

At the start of this year, work began on the Nelson–Marlborough Institute of Technology (NMIT) Arts and Media Building. The building is the first application of the Pres-Lam construction system in the world, planned for completion in early 2011. The Ministry of Agriculture and Forestry contributed $1 million towards the design and construction of the building as part of its Wood Building Demonstration Project, a government initiative to encourage innovation in design and the use of wood products in new multistorey commercial buildings.

Designed by Nelson firm Irving Smith Jack Architects, the building can’t compete with Dubai’s tower, but in some ways it is much more radical, heralding the welcome return of wood to multistorey commercial design.