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Concrete evidence
Published:  21 May, 2007

Being timber, KLH panels also score ahead of concrete and steel in terms of sustainability

KLH UK’s cross-laminated timber can do anything concrete can – and often do it better. Keren Fallwell reports

Sitting on the floor of KLH UK’s offices in Clerkenwell is a celluar shape of cross-laminated timber that looks like a piece from a giant, Alice in wonderland jigsaw puzzle.

This curvy cutout, from a window aperture at Kingsdale School in Dulwich – KLH’s largest project in the UK to date – demonstrates the construction of the timber panels, and the surprising flexibility of something so solid and so heavy.

The structural panels, which comprise layers of timber set at right angles to each other, are made in widths from 70-256mm thick, depending on the application. Because of the nature of the panels, it is with concrete and steel that comparisons are drawn, rather than timber frame.

“It’s always dangerous to compare this with traditional timber frame because it’s a solid panel,” said Karl Heinz Weiss, director of KLH UK. “It’s not a frame which is stablised with two cover plates; it has all the structural properties within the panel. It’s actually acting in two directions structurally, like precast concrete. That’s why you can work with it as you can precast concrete, creating large spans, cantilevers or overhangs.”

All the panels, produced from PEFC-certified Austrian spruce and fir, are manufactured in KLH’s Austrian factory, which is itself built from cross-laminated lumber. Europe’s largest manufacturer and supplier of cross-laminated lumber, KLH’s process differs from its competitors in that it uses a steel press, rather than a vacuum press, which allows thicker lamination layers and the use of formaldehyde-free adhesive. The KLH product is also the only one that has full European technical approval.

The panels are kiln-dried to 12% moisture content which is “very important”, said Weiss. “The humidity shouldn’t be less because we’re actually using the humidity in the timber to react with the adhesive so it has to be 12% plus or minus 2%.”

As with concrete, the panels are both structure and finish; presanded in the factory the panels can be left exposed in the interior of the building. All service channels, right down to recesses for electrical sockets, are also done in the factory. This means architects and engineers have to finish their designs on time, although if last minute alterations are needed on site, it’s not a problem.

“Because it’s timber it’s very flexible,” said Weiss. “Even if you drill a hole on the wrong side you can plug it nicely. With concrete there’s no chance – you can’t change it easily – whereas with timber you still have a massive circular saw and you can trim it back.”

Being timber, KLH panels also score ahead of concrete and steel in terms of sustainability, even when the road transport from Austria is considered. KLH UK senior representative Craig Liddell said a breakdown of carbon emissions, in terms of timber miles, is done for projects. A single lorry journey from Austria will produce about 1.4 tonnes of carbon but this is offset by the 30 tonnes stored in the load of timber.

These figures will be reduced when a second factory opens in Sweden “in the middle of the woods”, enabling the panels to be shipped to the UK.

KLH has partners throughout Europe, “even in Greece and Spain where you don’t expect to have timber”, said Weiss, and it is making steps into the markets in the US and the Far East and, it’s early days, but possibly the Caribbean too.

Since the Austrian company established a presence in the UK in September 2005, it has clocked up a portfolio of projects that is surprising in its diversity – from the sports hall and music block at Kingsdale School to a private house in north London where the street frontage was just 2.8m wide. It is now working with engineers Techniker on designs for a seven-storey structure.

Speed of erection, aided by the fact that no scaffolding is required, is another advantage of KLH’s panels. The structure of a house can be erected in two or three days, while Kingsdale School’s 20x75m sports hall was bolted into place in less than a month. The main structure - comprising 3x15m panels – went up around an independent two-storey cross-laminated building which houses changing rooms, offices spectators’ area.

In the adjacent music block architects de Rijke Marsh Morgan took advantage of the panels’ flexibility by producing fluid shapes for the windows – hence the exhibit in KLH’s offices, which looks as though it’s been shaped by a giant pastry cutter.

In contrast to the large sports hall, KLH has also supplied panels for the Focus House – a three-storey, three-bedroom north London home by Bere Architects. The house was originally designed in concrete but a value-engineering exercise found that cross-laminated lumber was more cost-effective and there was the added benefit that some of the design features – a corner window and the office which is cantilevered over the front entrance – were easier in timber.

The site is only 2.8m wide at the front, fanning out to 7m at the rear. The pre-cut walls, floors and roof were craned into place, again removing the need for scaffolding.

“It worked well on site,” said Liddell. “Craning was slightly tricky but crane drivers working in London have probably come across worse.”

Other projects have included a single-storey office extension and a two-storey structure in Archway (where the contractor’s insistence on scaffolding, on health and safety grounds, caused some problems) while abroad, KLH cross-laminated panels have been used for a 100x40m equestrian centre in Sweden, for a development of 156 flats in Vienna, and, again in Austria, to create a 12m cantilevered terrace for an existing, historic building.

In the UK, the market has been quick to embrace cross-laminated lumber, although, Weiss said, some engineers are still cautious. However, this year, with a projected turnover of £3.5m, Weiss expects KLH UK to supply about 20 projects, which include schools, churches, community centres and residential properties, and cross-laminated lumber will be chosen for any one of its benefits.

Some people approach KLH because of their concerns about sustainability and then realise the added benefit of design freedom offered by cross-laminated panels. Conversely, for some, sustainability is not the only driving factor. “You’re also talking about modern methods of construction and offsite construction – it’s a combination of these things,” said Weiss.

And design flexibility is another selling point. “There’s no limit; that’s one of the selling features,” said Weiss. “Really the only thing that is difficult is very tight radiuses. But we are in a position to be able to sit down with architects and find a solution.”