Thermally modified wood is still a relative newcomer to the UK market, with around four years under its belt.
Cladding is widely reckoned to be one of its best applications, due to the heat treatment process improving key properties in the wood.
Its Finnish manufacturers say heating the wood to at least 180 degrees C reduces its equilibrium moisture content and removes resin, therefore improving dimensional stability and making the timber more resistant to decay.
Other benefits cited include increased thermal insulation properties, the rich brown colour the process gives timber, and a reduction in the need for preservatives. These, say suppliers, give the product an edge over many traditional timbers used for cladding.
ThermoWood, a registered brand name owned by the Finnish ThermoWood Association, is currently imported to the UK by Finnforest and Stora Enso, who in turn supply a number of merchants.
Both companies, together with UPM, are partnering BRE in ongoing testing of ThermoWood for cladding.
Stora Enso business development manager Duncan Mayes estimates ThermoWood sales (including decking) in the UK to be about 1,500m3-2000m3 in 2004, roughly 3-4% of global consumption last year.
He said sales have progressed “quite slowly” due to a lack of knowledge and experience in the product. There has also, to date, been a shortage stockists to actively service the product and promote it.
He said: “There are now many reference projects in the UK for cladding. The general opinion from merchants and potential stockists is that the best potential for the material is in the cladding sector.
Mr Mayes said the BRE‘s ongoing testing of ThermoWood cladding using different coating systems was going “very well”, and he believes it will underline the material’s suitability for cladding.
BRE’s initial assessment of ThermoWood in accordance with BS 8417, based on earlier research by Finland’s Technical Research Centre, gives the material a class three durability rating for a service life of 30 years. But testing by Stora Enso in Germany has yielded a higher class two rating.
Mr Mayes, a board member of the Finnish ThermoWood Association added: “We hope at the end of it [BRE testing], they will be able to give a more robust statement.”
Mr Mayes is also involved in a technical specification project which is intended to lead to a European standard for thermally-modified timber.
Stora Enso is currently supplying some regional merchants and several contracts have been signed with national merchants for its standard cladding products. “We expect to see a breakthrough this year.”
The company has just produced two documents on ThermoWood cladding, which it hopes will help generate more interest for merchants to stock it. Direct marketing will also be carried out among selected architectural practices. “Currently there is still limited knowledge among specifiers. This is something where we need to focus – the interest from those that have heard about the material is very good.”
Stora Enso ThermoWood cladding has been used as a weather screen in the upper sections of New Broughton School, Milton Keynes. Combining with traditional red brick, the cladding has bevelled edges for rain to run off, with gaps between each board for airflow.
Another project showcasing ThermoWood cladding is Grainger Homes’ £2m redevelopment of a landmark 1930s art deco building in Birmingham.
Pitmaston Court, which provides a range of one to three-bedroom luxury flats, features 3,000 linear metres of ThermoWood imported by Finnforest and supplied by Gainsborough-based John Brash & Co.
Cost-effective solution
Warren Dudding, head of UK marketing for Finnforest, said ThermoWood cladding products carry a material cost of approximately £20/m2, making it a very cost-effective solution for the Pitmaston development.
Mr Dudding said the heat treatment process enables the use of Scandinavian redwood in areas requiring a 30-year service life without the need for chemical preservative. “This is obviously of great benefit to developers and architects when doing lifecycle costings for its usage in a proposed development,” he said.
Stellac Wood Mikkeli, via Holland-based FHT Sales BV, will shortly become the third company to import thermally modified timber to the UK.
The company says its “Stellac Wood” product, to be launched soon, has met durability class one (very durable) for 75mm spruce heartwood sections during laboratory tests to Dutch standard EN 350-1. Durability class two was achieved for 25mm spruce boards.
Jerry Wilson of Sylvawood, the UK agent for Stellac, agrees the opportunities within the UK have yet to be fully realised, but believes thermally modified timber is set to gain ground.
“There is growing interest from many architects, and feedback gained from the general public has been positive to the point where end-users have started asking how to obtain the product,” he said.
