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ThermoWood 21 x 142mm Shiplap Cladding

Price From: (exc VAT) £4.97 (inc VAT) £5.96
(exc VAT) (inc VAT)
Price per linear metre £2.76 £3.31
Price per square metre £22.63 £27.16

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ThermoWood®  is produced using a chemical-free natural process. By heat treating only the finest Scandinavian Redwood to enhance the chemical and physical properties of the timber, ThermoWood®  offers an exceptional cladding material with outstanding durability, stability and insulation characteristics.

At a glance

  • Popular shiplap profile provides an appealing shadow line. Wider board allows for greater coverage
  • Thermally modified wood providing enhanced stability, less shrinkage, swelling, cupping and distortion
  • Attractive deep brown tones throughout
  • PEFC Certified
  • The finest ThermoWood® in the industry - created from strict and specific mill requirements for high quality and consistency

ThermoWood® Cladding - Shiplap Profile for an appealing shadow line

Silva's 21 x 142mm ThermoWood® Shiplap Cladding Profile provides a wide board and attractive shadowing effect owing to the slight gradient in the shiplap groove. 

Silva’s commitment to supplying consistent and high quality timber products is reflected in our latest cladding material - ThermoWood®. Our extensive supply network has led us to source the finest ThermoWood® available, from one of the world's leading producers of this innovative timber product.

ThermoWood® is produced using a chemical-free natural process. By heat treating only the finest Scandinavian Redwood to enhance the chemical and physical properties of the timber, ThermoWood® Shiplap Cladding offers an exceptional cladding material with outstanding durability, stability and insulation characteristics. 

Along with enhanced physical properties, the treatment also results in an attractive, consistent, deep brown tone for a beautiful appearance. Due to it's stability, Thermowood also takes and retains finish well, allowing for translucent or solid colour stains to be applied to create unique and striking buildings.

Suitable for commercial and residential buildings, ThermoWood® Shiplap Cladding meets the requirements of Durability Class 2 (BS EN 350), carries European Standard CE Mark certification and is recognised by the Building Research Establishment (BRE) which endorses a 30 year service life when used for cladding. 

Thanks to an improved durability against decay, ThermoWood® Shiplap Cladding is well suited to projects facing harsh weather conditions. The attractive appearance and exceptional dimensional stability also makes the timber an ideal choice for internal cladding.

ThermoWood® Cladding Properties:

  • Improved durability against decay
  • Resin removed
  • Reduced splitting strength
  • Slightly reduced bending strength
  • Improved dimensional stability
  • Consistent colour throughout the timber
  • Chemical-free, entirely natural manufacturing process
  • Reduced equilibrium moisture content

Recommended end use applications 

  • Exterior/Interior cladding
  • Outer doors
  • Shutters/ louvres
  • Environmental constructions
  • Sauna and bathroom furnishing
  • Flooring 
  • Garden furniture


Logging Selection Process

Only the finest raw materials are used which best suit Thermowood production in terms of type and quality. The timber species chosen are exclusively Redwood, that have fewer knot characteristics. The knots which do exist in the timber are sound and tight due to their structure, for a superb performing exterior cladding material.

In Nordic forest logging processes, trees are cut into three sections; Butt Log, Middle Log and Top Log. Silva's ThermoWood is produced from the top or middle log for a high quality, consistent product, with only the centre of the log used to ensure live-intergrown knots.

ThermoWood® Manufacturing Process

Thermal modification of timber is a clean, ecological process which enhances the properties of the wood. The process is completely natural and chemical free, using only high temperatures and steam to transform and control the timber's characteristics.

During the thermal modification process, timber is treated with high temperature (+212oc). Water vapour is used as a protective gas and heat conductor, enabling heating of the wood beyond its auto-ignition temperature. By heating the wood to 212oc, resistance to decay and dimensional stability are greatly enhanced, creating the Thermo-D properties suitable for exterior and interior cladding materials. 

Thermal modification can be divided into three phases:

1: Temperature of the wood is raised, then dried

2: Thermal modification takes place - Moisture content of wood is dropped to close to zero, and then heated to 212oc.

3: The treated wood is cooled down and moisturised to the desired level.

ThermoWood® Finish & Treatment

ThermoWood's dimensional stability provides an ideal exterior cladding material. With improved resistance to decay and weather conditions, ThermoWood® holds an unbeatable advantage in outdoor use. As with all timber, ThermoWood will naturally weather to a silvery-grey colour with prolonged exposure to the elements if left untreated.

To maintain the longevity and appearance of ThermoWood® , it is recommended to apply a surface treatment for added UV protection such as a penetrating oil, translucent finish or solid colour stain.

Read more


ThermoWood Horizontal Cladding installation

Finishing & Protection

Under the direction of Dr. Nenad Vidovic, the Sansin Research & Development team conducted extensive testing of Sansin's core line up of products in a variety of heat-treated wood applications. Sansin's test results confirmed that without suitable coating, heat treated wood is not weather resistant and particularly susceptible to UV degradation. For the optimal performance, Silva Timber recommend protecting ThermoWood with Sansin SDF HT using our pre-finishing service.

Why Pre-finish?

  • Enhances the natural beauty of wood
  • Ensures a consistent finish
  • Applied in factory conditions
  • Long lasting protection against weathering
  • Simple maintenance routine
  • Reduces onsite labour costs

Sansin Enviro Stains

Easy to apply and maintain, Sansin Enviro-stains deliver outstanding performance. Sansin's range of wood protection products are available in 80 colour tones

What is weathering?

There is a risk involved when leaving wood exposed to the elements. During the weathering process wood can appear unsightly as the material can blacken due to moisture getting into the fibres and pulling out tannins and extractives. Finish protects the wood from moisture absorption and UV degradation.

What to expect from timber products

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.


ThermoWood® is a registered trademark owned by International ThermoWood


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 to 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 carries 
Programme for the Endorsement of Forest  Certification  (PEFC)

The PEFC Council 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


  • FSC
  • PEFC
  • Trada member
  • Responsible purchaser
  • Cedar Shake & Shingle Bureau
  • nbs plus
  • Secured by