What is ThermoWood?

ThermoWood is a beautiful and entirely natural wood product that is created using natural methods, the roots of which date back thousands of years. Nordic grown pine undergoes a patented natural process involving heat and steam to permanently alter its physical properties.

This thermal modification process greatly improves dimensional stability, durability and thermal insulation properties. It also removes resin and even changes the colour of the wood to a pleasing rich dark brown colour.

ThermoWood is completely natural and free from chemical additives, thus it is an exceptionally environmentally friendly building material.

There are two standard treatment classes which have been developed to take into account the key characteristics of ThermoWood. The standard treatment classes are named Thermo-S (for internal use) and Thermo-D (for internal and external use). Silva’s ThermoWood cladding is classified as Thermo-D (D stands for ‘durability’), which is recommended for end uses such as exterior cladding and decking. It has a decay resistance of durability class 2 (durable) according to the EN 113 standard which is the same classification given to Western Red Cedar.

Raw Material

Silva’s ThermoWood cladding is produced from high quality Nordic Pine. It is grown mainly in Finland, one of the best areas in the world for tree growth. Sub-zero winters alternate with short warm summers which results in slow growth.

The slow growth provides the best possible straight-grained timber: branches and therefore knots are few in number and those that exist are small. Growth is symmetrical and trunks are straight and round. Growth rings are thin and tightly-packed. The amount of juvenile wood is small and heartwood great. The result is a hard, tough and straight-grained timber with low internal tension and minimal cracks. The low-resinous, evenly patterned Finnish wood is first-class material for many purposes.

This profile is available exclusively through Silva. It is sustainably sourced from well managed forests and supplied with full PEFC chain of custody certification.

Production Process

The thermal treatment of wood is an ancient and natural method for improving its durability. The manufacturing process of ThermoWood is based on the use of high temperature and steam. No chemicals are used in the treatment. The process improves dimensional stability and biological durability of wood. Another improvement is in the insulation properties of the final material, the process leads to a reduction in thermal conductivity. Due to the high treatment temperatures the resin is removed from the wood. The ThermoWood treatment process is patented and the trademark is owned by the Finnish ThermoWood Association. .

Widths and Lengths

ThermoWood Channel cladding is available from stock in the following sizes:

Widths: 21 x 118mm

You can check current stock availability and select your chosen board width and length(s) from the drop down menu above.

Surface Texture

This ThermoWood V-Joint cladding has a fine sawn textured surface known as SAWtex®.

SAWtex® = Better Looking and Longer Lasting Coatings

The SAWtex® surface is recommended if the cladding is to be factory coated or if a coating is to be applied in situ.

This special surface texture has two benefits:

1. Wood scientists have proved that a textured surface will accept and retain finish significantly better than a smooth planed surface, thus improving appearance and minimising future maintenance. The SAWtex® surface enables the coating to penetrate deep into the wood, rather than it just sitting on the surface as it would with a planed surface. The result is deeper, richer and more consistent colour because more stain is in the wood and the overall level of penetration is more even.

2. The SAWtex® surface gives this cladding a beautiful natural appearance that makes the wood grain more visible and exudes a feeling of warmth, adding an extra layer to its appeal.

Save time and money - order your ThermoWood cladding factory coated

According to the Finnish ThermoWood Association, the application of a coating is necessary to protect the wood from the damaging effects of moisture and UV, to help prevent the wood from turning grey and to curb the growth of fungi that produce mould or blue stains. Thermally modified wood can be finished in the same manner as normal wood.

The Finnish ThermoWood Association also point out that it has to be taken into account that ThermoWood has a lower water absorption rate than normal wood and that this can have an effect on the penetration and drying time of the coating.

For this reason Silva uses a specially adapted formula of Sansin Enviro Stain – called SDF HT - which has been developed specifically for use on heat treated wood.

Save time and money by ordering your ThermoWood cladding factory coated. It’s delivered to site ready to install at any time of year.

A complete range of cladding materials

When working with timber it should be expected that although ‘on-grade’, occasional boards may have minor imperfections that will require ‘working’ if you wish to eliminate. Examples include raised grain, small splits, minor handling marks, sticker marks etc – all of which can easily be remedied by trimming, gluing or sanding. In most cases imperfections can be removed with very little effort, and the small amount of off cuts generated as a result will be absorbed in the normal cutting and selection allowance.

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Grades

Silva Timber’s ThermoWood is modified to Thermo-D (Durability) standards. Biological durability is an essential characteristic for end use applications in this treatment category. The average tangential swelling and shrinkage due moisture for Thermo-D class treated wood is 5-6%, Thermo-D class ThermoWood is classified as durable according to the EN113 standard – meeting Class 2 requirements.

This product is PEFC certified.

PEFC (Programme for the Endorsement of Forest Certification) is an independent, non-profit, non-governmental organisation founded in 1999 which promotes sustainably managed forests through independent third party certification. The PEFC provides an assurance mechanism to purchasers of wood and paper products that they are promoting the sustainable management of forests.

PEFC works throughout the entire forest supply chain to promote good practice in the forest and to ensure that timber and non-timber forest products are produced with respect for the highest ecological, social and ethical standards. Thanks to its  eco-label, customers and consumers are able to identify products from sustainably managed forests.

Silva Timber meets the requirements for PEFC Chain of Custody within the BM TRADA Certification Limited Scheme for TRADA - Trak chain of custody certification.

Certificate number: BMT-PEFC-0319