July 2, 2010 8:44 pm

Timber, but not as we know it

It is one of the oldest and most reliable building materials known to man, and yet for many years, outside northern Europe and eastern countries such as Japan, timber has been considered a lesser construction ingredient. To the wider public and building trade, wood is what you use to frame a structure or to create lovely exterior cladding. We might feel a nostalgic connection with the giant oak beams of a medieval building, but rarely do we think of timber as a material for the future. However, that is changing.

“It’s an exciting time for wood,” says John White, chief executive of the UK Timber Trade Federation. “People like it for its sustainability, that it’s a renewable resource and doesn’t have to be manufactured.” But this is only scratching the surface of why timber is becoming increasingly popular as a building material.

 
Anne Tornberg and Lutz Volke

Alternative: Anne Tornberg and her husband Lutz Volke used Kebony to clad their seaside house in Norway

A range of engineered wood “products” that have been used for decades in Scandinavia, Switzerland, Germany and Austria are now making their way around Europe and beginning to take hold in the UK and US. These range from soft woods that have been treated in new, non-toxic processes, so that they can be used for decking and cladding, to giant “jumbo-ply”, as one architect calls it, that can replace concrete and steel to form the structure of a building. These products have been used increasingly across Britain for new schools and public buildings. Now architects and builders are using them for private housing, with some impressive results.

These aren’t your typical log cabins. The revolution is in sophisticated timber products that can be used as solid walls, floors and supports to construct not just the frame but a whole building. These structural laminates are made by pressing wood together in the same way as with standard ply but in panels up to 50cm thick. Champions of the new laminates point out that not only is wood a renewable resource but that trees, as a medium for carbon storage, help reduce CO2 emissions merely by being used and replanted. There are other benefits to consider: wood, which is much lighter than brick, steel or concrete, requires less energy (and is cheaper) to transport. Also, structural laminates make use of lower quality softwood that can be cheaper and more abundant than hardwoods and, in places like the UK, locally grown. With a lifespan that is comparable to concrete or brick, solid timber is an increasingly popular option.

One convert to structural laminated timber is Andrew Waugh, whose firm, Waugh Thistleton Architects, completed the world’s tallest solid-wood residential structure in Hackney, east London, in 2009. Murray Grove (also called Stadthaus) is a nine-story building that contains 19 private and 10 subsidised apartment units. It has a solid wood core – walls, floors and ceilings, even elevator shafts – though the foundation was laid in concrete to minimise risk of damp. The main construction material is cross-laminated timber, or CLT, made from dried spruce boards stuck together. While the use of solvents is still an environmental issue, Murray Grove used a non-toxic, water-based adhesive.

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As with most prefab builds, the construction time was extremely quick: it took just under a year to complete the building of Murray Grove. Using concrete, says the architect, would have taken 18 months.

A similar product, from Germany, is the main element in another project in north London by Stephen Coleman of 4orm architects, where mechanically laminated timber has been used to build four houses in Highbury . Softwood is also used, but without adhesives: the sheets are held together by beechwood dowels.

Coleman and his client Pieter Brons, a Dutch property developer, were interested in prefabricated systems and originally looked at concrete panels before considering the timber alternative. As a German speaker, Brons went directly to German manufacturers, which he estimates saved him 20 per cent in building materials compared with using concrete or brick, even with having to transport the materials to the UK. Yet, some architects and builders will point out that solid timber isn’t always a perfect alternative to concrete and may be restrictive when trying to create curved forms or expansive windows.

Both the Murray Grove and Highbury projects subscribe to standards set by Passivhaus, an efficiency certification programme that began in Germany in 1990 and has spread to 17,000 homes worldwide. It establishes targets in building, energy efficiency and air quality so that certified houses are 90 per cent more efficient than standard housing units. Both the PassivHaus programme and British government targets for zero-carbon houses by 2016 are doing a lot for the promotion of timber building in the UK, according to Steve Oxley of Sustain magazine. But environmentalists are uncomfortable with the idea that “once you build in wood, you’re done,” he adds. “They feel people should still try to do more.”

There is also some hesitation among the public about using wood. “Many people associate timber buildings with those badly built timber-framed houses of the 1960s and 1970s,” suspects Coleman. “They had such terrible press and very poor acoustics, which this solid wood definitely doesn’t.” And people worry about fire. “But again, most people are thinking of timber-framed buildings, not solid wood,” he says. “Wood will char before it burns, and with such a large surface area, this protects the wood.”

Perhaps it is the great irony of the Highbury houses and Murray Grove building that although both represent achievements in modern design using solid timber construction, the wood is not visible.The rooms are finished with plasterboard and painted, as with any new build. Marco Lindl, one of Murray Grove’s first residents, is impressed. “The timber construction gives the whole building and each flat a very warm feeling which I think cannot be achieved in a steel- or concrete-constructed building,” he says. “The soundproofing is excellent: we cannot hear our neighbours at all.”

There have also been strides in using wood that is visible. New, non-toxic methods in treating soft wood species means that some can now be used for cladding, decking and flooring in place of tropical hardwoods. A Norwegian product called Kebony uses alcohol and sugar to harden wood such as beech, southern yellow pine, maple, Scots pine and ash permanently, so it becomes moisture- and insect-resistant, as well as weatherproof. After decades in development in Canada and Norway, Kebony was launched on the international market last year, and has been taken up for public decking and boardwalk projects in the US, and on buildings for the Forestry Commission in Scotland. One devotee is Norwegian architect Anne Tornberg, who clad a small cabin overlooking Olso fjord in the material. “In Norway there is a strong tradition of building in wood, unlike the UK, and there is also more extensive use of other alternatives to traditional [chemically] impregnated timber. But we chose this material because we liked it for its qualities, its warmth, that it’s cheap to use and environmentally friendly.”

Martin Despang, an architect based in Dresden, Germany, who teaches at the University of Nebraska in the US, has recently used ThermoWood, a similar product to Kebony, to restore the interior woodwork of a house in Hanover, Nebraska. He has also built a school in the material, and is campaigning to bring more innovation in timber to both his home and adopted country.

Phyllis Richardson is the author of the ‘XS’ series, published by Thames and Hudson

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