Thermally Modified Cladding


Thermally Modified Cladding Thermally Modified Cladding such as ThermoWood Cladding offers outstanding durability and stability with an increased resistance to decay and excellent water-repellence and weather protection.

The modification process increases the durability of the wood and therefore extends its service life. The process also improves the woods thermal insulating properties through a 100% chemical free, natural transformation.

ThermoWood Process

ThermoWood® Manufacturing Process

Thermal modification of timber is a clean, ecological process which enhances the properties of the wood. The process is completely 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 moisturized to the desired level. 


ThermoWood Properties

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 accoring to the EN113 standard - meeting Class 2 requirements.


Summary of the effects of the Thermowood process on wood properties:

Property Thermo-D
Treatment Temperature 212oc
Weather Resistance ++
Dimensional Stability ++
Bending Strength -
Colour Darkness ++


Finishing and Maintenance

It is recommended that a finish is applied to all surfaces, including ends, before installation. The type of coating wil be determined by the final finish and appearance desired.

Finish protects the wood from moisture absorption and UV degradation. It helps prevent staining caused by mildew and extractives and will increase the service life of the timber.

Consider one of our stunning finishes from the Sansin exteriors range. Click here to view the Sansin brochure.

A wide range of coating and stains are available to view here.

Silva Timber also offer a pre-finishing service, reducing installation time and on-site preparation.

Feel free to discuss your finish requirements with our customer support team on 0151 495 3111 or 01895 271 300. Alternatively email

PEFC Certification

ThermoWood - PEFC Certified

Schemes 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

Fire Treatment


Unique Fire Protection

When you need to comply with Building Regulations on fire protection, Silva can offer timber products impregnated with fire retardant treatment.  Specify either DRICON® for interior or weather protected situations or NON-COM® EXTERIOR for exterior or severe damp situations.

These proven industrial pre-treatments for timber and related substrates are applied under controlled conditions at the Arch Timber Protection’s ISO certified Fire Retardant Treatment Centre in Castleford.

The standard lead time for both DRICON® and NON-COM® EXTERIOR fire retardant treatments is 8 weeks.  Treatments can be applied to kiln dried Western Red Cedar cladding, trim, decking, shingles and shakes; Siberian Larch cladding and Eastern White Cedar shingles. Please contact us for further information or a quote.

Making sure you specify the correct fire protection is vital. Click here for the main considerations when specifying fire retardant protection for timber,that can help save fire damage costs and people's lives.

For detailed Frequently Asked Questions please click here.





Fire Retardant Treated Timber for Exterior or Severe Damp Situations

NON-COM® Exterior treated timber has been impregnated with NON-COM® Exterior fire retardant, a leach resistant, polymer based formulation which is an approved Type LR (leach resistant) formulation in the Wood Protection Association (WPA) Flame Retardant Manual.

NON-COM® Exterior is a Leach Resistant (type LR) fire retardant treatment suitable for exterior or severe damp situations without the need for a protective coating. However an approved coating can be applied if required. Ensure the coating to be used is compatible with NON-COM Exterior fire treated timber.
NON-COM® Exterior is available to conform with either Class B or Class C certification, depending on the application requirements. 

  • Allows you to meet fire regulations with a commercially proven, global product backed by extensive independent test data.  
  • Meets all relevant British and European Standards.
  • Fully fire tested in accordance with European Standards (Euroclasses) under the Construction Products Directive and classified in accordance with EN 13501-1.
  • Fully tested to BS476, Part 6 'Fire Propogation Test' and Part 7 'Surface Spread of Flame' .
  • Excellent appearance - leaves the appearance of the natural timber product virtually unchanged. 
  • Can be used externally, with or without a coating. 
  • Waterbased formulation applied by vacuum-pressure impregnation in factory controlled conditions, to ISO 9001 Quality and ISO 14001 Environmental standards. 
  • Kiln dried to end use moisture content. No strength reduction of treated timbers, and no corrosion of metal fastenings and fixings. 
  • Specification writing service available.

Silva Timber's Non-Com fire retardant treatment service provides the following assurances and benefits. When comparing our service to competitors, be sure to check the following are offered for a like-for-like comparison

  • Long history of proven performance
  • Accepted by the National House Building Council (NHBC) Building Control Service for exterior timber cladding
  • Independent classification reports for each timber species, timber thickness, for use with or without air gaps - BS EN 13501-1
  • Products listed by the UK Wood Protection Association
  • Products approved by the Fire Protection Association
  • Lasts the lifetime of the building with no maintenance - meets current FR durability standards - tested to TS 15912
  • Applied by an ISO 9001 and ISO 14001 accredited company
  • Applied to all faces of the timber product
  • Applied by a controlled impregnation process
  • From a supplier operating to the UK Wood Protection Association Quality Scheme
  • Treated with products manufactured by the supplier
  • Available for a wide range of species
  • Reduces smoke generation
  • Non-corrosive to metal fastenings
  • Does not reduce the strength of the timber
  • Non-hygroscopic - does not absord water or give rise to efflorescence
  • Can be used for exterior timbers without a protective coating
  • Treated products flee from surface salt deposits
  • Treated products have enhanced biological durability





Fire Retardant Treated Timber for Interior and Weather Protected Exterior Situations

DRICON® treated timber and sheet materials have been impregnated with DRICON® fire retardant, a water-based formulation which is an approved Type HR humidity resistant formulation in the Wood Protection Association (WPA) Flame Retardant Manual.

DRICON® is a Humidity Resistant (type HR) fire retardant treatment suitable for interior and weather protected exterior applications with or without a coating to the fire treated timber or plywood. It can only be used in an external situation prone to direct wetting if a well maintained protective coating/paint/stain is applied. Ensure the coating to be used is compatible with DRICON® fire treated timber/plywood as appropriate.

Please be aware DRICON® is not recommended for application on Western Red Cedar.

  • Allows you to meet fire regulations with a commercially proven global product backed by extensive independent test data.
  • The ONLY BBA certificated fire retardant treatment for timber (Certificate No 87/1841).
  • Fully fire tested in accordance with European Standards (Euroclasses) under the Construction Products Directive and classified in accordance with EN 13501-1.
  • Fully tested to BS476, Part 6 'Fire Propogation Test' and Part 7 'Surface Spread of Flame' .
  • Meets all relevant British and European Standards including the Construction Products Directive for panel products for used in permanent constructions.
  • Water based formulation applied by vacuum-pressure impregnation in factory controlled conditions, to ISO 9001 Quality and ISO14001 Environmental standards.
  • Non-hygroscopic formulation - unaffected by high and fluctuating relative humidities.
  • Does not significantly reduce strength of treated timber, non-corrosive to metal fastenings and fixings, does not affect paint finishes and adhesives, and is maintenance-free.
  • Specification writing service available.


To discuss your requirements, please feel free to contact our customer support team on 0151 495 3111 (Cheshire) or 01895 271 300 (W.London).

Case Studies