There might not be an obvious link between a bridge in Holland, a chair in Germany, and a cricket clubhouse in Edgeworth. But, while they might be poles apart in terms of construction techniques, these three structures are pushing the boundaries by using the latest generation of modified timbers to hit the European market.

Big companies are putting money and marketing muscle behind a new breed of timbers, which, thanks to their modification, can offer end users increased durability, stability and product life, with the added benefit of low maintenance.

The modification techniques differ from manufacturer to manufacturer and, while their potential remains largely untapped, their use in timber building construction has so far been limited to cladding and decorative techniques (except in the case of Glenalmond Timber’s Ultrajoist, which has been picked up by several large housebuilders to form a construction solution).

However, products like Finnforest’s ThermoWood, used mainly for cladding, Osmose’s Indurite system, used for flooring, doors and window frames, and Titan Wood’s Accoya, are at the cutting edge of technology – and increasing in popularity.

This popularity is borne out by their benefits. When Edgworth Cricket Club briefed designer and builder Rothwell Robinson on its new clubhouse, the main stipulation was that the new building would require very little maintenance.

Rothwell Robinson chose ThermoWood, a product that combined the performance characteristics the club was after with the aesthetics that only timber can deliver.

ThermoWood, used as cladding on the Edgworth Cricket Club, has a 30-year service life without treatment

It’s no surprise to Phil Nash, product and specification manager for ThermoWood at Finnforest. “So long as it is installed in the correct manner, ThermoWood can give a 30-year service life without any treatment being applied,” he said.

Finnforest’s ThermoWood is engineered from Finnish European redwood and is produced by an intensive heat treatment – baking the wood at temperatures exceeding 200OC. The chemical changes in the timber that occur during the heating and drying process result in what is said to be a more stable product, and one that Finnforest claims is superior in its resistance to the effects of moisture, insect and fungal decay. This makes it ideal for external applications such as protective cladding, but it is also eminently suitable for decking and other landscaping applications.

“We are marketing the product towards national housebuilders, architects and end users,” said Nash. ThermoWood is currently being used in a new retail park in Bambridge, Northern Ireland, where around 200m3 will be used as external cladding as well as a decorative glulam. Other recent projects include a Sainsbury’s supermarket at High Wycombe and social housing projects in Norwich.

Another thermally-modified timber new to the UK is Plato Wood, a product currently manufactured in the Netherlands and being marketed in the UK by Ecochoice Ltd. Like ThermoWood, it uses heat for modification but, unlike its rival, the treatment takes place at lower temperatures. The process, claims Ecochoice, results in an end product with a range of beneficial properties; extreme durability, shape retention, low moisture content and ample bending strength. The product also carries Forest Stewardship Council certification.

In the Netherlands, Accoya is being used for a 31m, dual carriageway bridge

“The treatment doesn’t include any chemicals,” said Ecochoice managing director Mike Bekin. “The process takes the wood up to 160OC, which causes a chemical reaction inside and the finished material is more stable than before it entered the kiln. In effect, the process has killed the organic matter that would have rotted it over time.”

The main wood being treated is FSC-certified Nordic spruce. While in Europe, Plato Wood’s stability (it has a 15-year minimum guarantee) is proving to be successful for decorative applications like cladding, Bekin said it could also be used for structural applications. The first deal has recently been signed for its use in the UK, providing external louvres for a small development in London.

Ecochoice is also looking for UK distributors: Palgrave Brown is believed to be the first company to sign up the product. “Plato Wood is positioning itself as a more complex product,” said Bekin. “The process also reduces brittleness so it can be used for a wide range of applications, including small civil engineering projects and uses in harsh, wet environments.”

Osmose’s Indurite is a water-based impregnation system. The formulation contains a modified natural polysaccharide: put simply, it’s very similar to cellulose, wood’s principal component.

“What we are actually doing is making a water-based formulation that is similar in structure [to wood],” explained Osmose’s Andy Hodge. “Under pressure-impregnation, we put as much into the timber as possible: the more permeable the timber, the better effect you will get. We are trying to create a natural composite; if we are able to fill up the cells with a similar solution to the wood itself, once it’s cured, we end up with a denser piece of material.”

Plato Wood is proving successful for decorative applications, such as cladding, because of its stability

This, he said, creates increased hardness and strength improvement and resultant increases in dimensional stability. Osmose is also able to change the appearance of the wood: using the Indurite process with more permeable species, it is able to add a pigment so that a treated softwood not only acts like a hardwood, but looks like one too.

Osmose sees a range of uses for Indurite, mainly as an internal product like flooring, furniture, doors and windows and decorative panels: any application where a combination of strength, dimensional stability and appearance are essential.

“Some of our research shows that there are some popular ‘light’ hardwoods that actually don’t perform well when you put them into flooring,” said Hodge, “so there is the possibility that we can use Indurite on certain types of hardwood.”

Hodge said Osmose is “discussing applications with companies in different countries”, with a view to commercial production in the near future. The next step will be looking at possible external application.

BSW Timber is the exclusive supplier for the UK and Ireland of Titan Wood’s Accoya, a product that is already being used in high-profile jobs, such as the 31m bridge currently being built in northern Holland. This full dual carriageway structure has no restrictions on load, and so a product was needed that delivered high stabil-ity and long-life. The builders chose Accoya because of its inherent strength and performance characteristics.

Accoya is a chemically-modified softwood, designed to increase the naturally occurring acetyl wood compounds. Pine, for example, would normally contain 2% acetyl groups – with Accoya, this figure increases to 20%, which prevents moisture – whether water or vapour – being absorbed into the wood.

Plato Wood can be used for a wide range of applications, including small civil engineering projects and use in harsh, wet environments

“By keeping moisture out, we are preventing decay organisms or fungi from attacking the wood,” said BSW Timber’s head of business development John Alexander. “These need a certain level of moisture in timber before they can start degrading it – we are cutting off that opportunity, so they are not interested in eating it.”

Eliminating the moisture also prevents the wood from shrinking or swelling, or going through big fluctuations in moisture content. This means doors and windows won’t stick in their frames, or cladding twist and have its dimensions come out of tolerance. Shrinking and swelling also put a high level of exertion on coatings, whether they are opaque paints or translucent wood stains. “If the wood behind the coating is moving out and in, that’s an awful lot of strain, so we are eliminating one of the key causes of premature failure,” explained Alexander. This durability means Titan Wood promises much longer lifespans without degradation – at least 50 years when used out of ground. The company is also working with Akzo Nobel Sikkens to develop coatings with longer-life guarantees, up to 12 years when factory-applied.

Titan Wood’s chief executive officer Eddie Pratt said acetylation – the process by which Accoya is created – is the “holy grail” of wood modification. “Although we work with pine species, the end product is so completely different in terms of its performance that the advice we’ve been given by scientists is to re-label it as a new species.”

John Alexander also thinks the timing is right. “There is a better awareness of timber and we believe that we are offering a product that is very much in line with the eco-assessment tools that are in industry,” said Alexander. The first commercial plant is due to be commissioned in the Netherlands in October and commercial volumes should be available from then.

Other big companies have also joined the fray. Earlier this year, German chemicals giant BASF unveiled the first fruits of its new Belmadur technology – a cantilever chair for outdoor use, using shaped beech wood.

The company, which has spent e3-5m developing Belmadur, believes the technology will widen the range of applications for species such as pine and beech in flooring, windows, doors, cladding, decking and garden furniture.

Belmadur is applied to wood by normal pressure impregnation methods and involves the cross-linking of cellulose molecules within timber. The company claims the process increases the dimensional stability, hardness and durability of wood, making beech as long-lasting as teak and twice as hard as oak. The company is still investigating the potential of its new technology, but hasn’t ruled out that it could be used for bigger spans.

The Accoya process prevents moisture being absorbed so joinery will not stick

One company that is enjoying repeat business for its modified product is Glenalmond Timber, the first licensee and accredited manufacturer of Ultrajoist solid timber joists. Ultrajoist is proven to significantly reduce the damage and associated costs resulting from timber shrinkage in centrally-heated buildings. The company has developed strict factory conditions to guarantee the environmental and performance characteristics of the joists – wherever they are manufactured.

So far, Glenalmond has supplied Ultrajoists for hundreds of buildings, such as the 300 new private houses built by Malcolm Allen of Aberdeen. It’s also been used by Prestoplan for the upper storey ring beams in its timber frame buildings.

“The main benefit for us is not to be regarded as solid timber but as an engineered – or modified – product,” said Glenalmond Timber’s Fraser Steele. “The benefits are that it is pre-shrunk or pre-conditioned so it is not going to move in situ. A lot of timber frame manufacturers are now using Ultrajoist for their top and bottom plates for their panels, because that’s where you get the most differential movement.”

The company is also about to test its flood potential and is looking at incorporating it in a glulam product that could provide spans up to 9m. “It’s taken us five years to get to a point where the product has become more widely accepted, but this is the first year where we are really seeing significant growth,” added Steele.

“It gives designers finite parameters to work in rather than sticking their thumb in the air and guessing. In today’s industry, no-one can guarantee the moisture content of timber.”