Fire Retardant Treated Timber FAQ

  1.  What is the difference between DRICON and NON-COM Exterior fire retardant treatments?
  2.  How do fire retardant treatments for timber work?
  3.  What industry standards do Arch fire retardant treatments meet?       
  4.  What timbers can be DRICON treated?
  5.  What materials can be NON-COM Exterior treated?
  6.  What are Class 1 and Class 0?
  7.  What are Euroclasses?
  8.  What fire performance is required for external timber cladding?
  9.  Can you fire treat OSB board or MDF?
10.  I want to fire treat a staircase. Which treatment should I be looking at?
11.  What will be the weight increase to fire retardant treated timbers/plywoods?
12.  What fire retardant treatments are suitable for use on the London Underground system?
13.  How does gluing affect treatment/treated timbers?
14.  Can I fire treat timbers to be used within indoor Swimming Pools facilities?
15.  How should waste treated timbers be disposed of?  


1.  What is the difference between DRICON and NON-COM Exterior fire retardant treatments?

DRICON is a water-based, Humidity Resistant (HR) type formulation that is applied under controlled conditions in a vacuum pressure impregnation plant, followed by kiln drying to return the timber to an acceptable or specified moisture content.  The DRICON treated timber/sheet materials are suitable for all interior applications and also for weather protected external use - materials must be protected from direct wetting by the application of an applied and properly maintained stain or paint finish.  Typical end uses for DRICON treated material would be internal building timbers, linings material, staircases and scaffold boards (please discuss first with Arch Timber Protection).

NON-COM Exterior is a polymer based, Leach Resistant (LR) type formulation.  It is applied to the timber/sheet material by the same process as DRICON - pressure impregnation process and kiln drying - but the treated material is then also subjected to a high temperature curing process to return it to an acceptable or specified moisture content.  The NON-COM Exterior treated timber/sheet materials are suitable for full exterior and severe damp applications, without the need of a protective coating, although material can be decorated, if desired.  Typical end uses for NON-COM Exterior treated material would be exterior cladding, exposed timber structures and cedar shingles and shakes.

2.  How do fire retardant treatments for timber work?
When subjected to fire, the chemicals in both DRICON and NON-COM Exterior treated materials react with the combustible gases and tars normally generated by untreated wood, converting them to carbon char, carbon dioxide and water vapour. The insulating layer of char formed on the timber retards the process of combustion, reducing ignition, the rate of surface spread of flame and the amount of heat released, all providing additional time for the safe escape from the burning structure.

3.  What industry standards do Arch fire retardant treatments meet?
The fire performance for all materials that are to be used in buildings, including wood and wood based panel products, are stated in Document B of the UK Building Regulations.
Requirements are expressed as a classification:

•  The performance normally required for wall and ceiling linings is Class 1 Surface Spread of Flame in
    accordance with BS476:Part 7 or Euroclass C in accordance with BS EN 13501-1: 2002.
•  The performance normally required in higher risk areas such as escape routes and staircases is
    Class 0 BS 476: Parts 6 & 7 or Euroclass B in accordance with BS EN 13501-1: 2002.


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4.  What timbers can be DRICON treated?
A wide range of timber and sheet materials can be treated with DRICON.  Please contact us for advice on treating to meet specific standards or if the materials you intend to use is not shown below.

SOLID TIMBERS

•  Western Red Cedar, Siberian Larch, Tulipwood, Willow, Sycamore

•  European Whitewood, European Redwood, Hem-Fir, Hemlock, Douglas Fir

•  Maple, Oak, Ash, Sapele, Mahogany, Accoya®

WBP PLYWOODS
•  Far Eastern, Far Eastern Marine, Gaboon or Okoume, Spruce, Douglas Fir
•  Birch throughout, Birch Combi, Flexiply®, Bendiply


5.  What materials can be NON-COM Exterior treated?
A wide range of timber and sheet materials can be treated with NON-COM Exterior.  Please contact us for advice on treating to meet specific standards or if the materials you intend to use is not shown below.

SOLID TIMBERS

•  Western Red Cedar, Western Red Cedar Shingles and Shakes*

• Siberian Larch, Douglas Fir, European Whitewood*, European Redwood, Hem-Fir, Hemlock
• Thermowood®, Plato®wood, Iroko, Red Louro, Oak
•  Oak Shingles and Shakes*, Accoya®

WBP PLYWOODS
•  Far Eastern, Far Eastern Marine, Gaboon or Okoume, Spruce, Douglas Fir
•  Birch throughout, Birch Combi
SPECIFIC COMMODITIES*
•  Cedar Shingles, Oak Shingles, Whitewood, Yorkshire Boarding

   *Complies with BS476: Part 3 AA/P60 Roof Penetration Test.

6. What are Class 1 and Class 0?
These are classifications of fire protection for timber within BS 476 Part 6& 7 and measure of the lateral spread of flame along the surface of a timber component.  Class 1 conforms to BS 476 Part 7 and is the performance normally required for wall and ceiling linings.  Class 0 is a more stringent requirement to BS 476 Parts 6 & 7 and is normally required in higher risk areas of a building, such as escape routes and staircases.  To achieve Class 1 BS 476 Part 7 classification, the spread of flame must not be more than 165mm in 10 minutes.  Class 0 BS 476 Parts 6 & 7 classification embodies the requirements of the surface spread of flame (Part 7) as above but also Part 6 which is known as the 'fire propagation index', a measure of the heat released when timber burns.  Timber achieving a Class 0 specification must achieve a fire propagation index of I ? 12 & a sub-index I 1? 6.

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7.  What are Euroclasses?
Under the Construction Products Directive, there is a move towards European harmonisation of standards for fire retardant treatment of timber - Euroclasses B & C.  To meet Euroclass B or C Specifications, timber/plywood is tested to EN ISO 11925 (Ignitability Test) & BS EN 13823:2002 (SBI or Single Burning Item Test).  The SBI test records parameters relating to the rate of fire growth, lateral flame spread and total heat release.

Euroclass Classifications are in accordance with BS EN 13501-1 (Fire classification of construction products and building elements). The thresholds for compliance in relation to the above SBI criteria are higher for Euroclass B than for Euroclass C. Therefore, by definition, if timber/plywood conforms to Euroclass B then it also conforms to Euroclass C. In England and Wales, the fire requirements for buildings are dealt with by Approved Document Part B to the Building Regulations - Class 0 and Class 1.  Euroclass B transposes to Class 0 and Euroclass C transposes to Class 1.

PLEASE NOTE: It is not possible to obtain a national class and sell to a European Class or vice versa. In other words, you must carry out testing against European Standards to achieve a European Classification.

8.  What fire performance is required for external timber cladding?
The fire performance of timber cladding for a building is commonly stipulated by Building Control - this is usually either Class 1 BS 476 part 7 or Class 0 BS 476 Parts 6 & 7, with Class 0 being the higher level of fire protection.  The main criteria when determining the fire performance required is the proximity of the building in relation to those around it.

If an elevation or elevations of a building are within 1 metre of a boundary, then a Class 0 specification is usually required. Commonly, the timber battens and horizontal fire stops should also be treated as well as the timber cladding.  Occasionally Building Control will stipulate a 30 minute or 1 hour Fire Resistance. This relates to the fire performance of the STRUCTURE as a whole, not just the cladding. If this is the case, we recommend you seek advice from Arch Timber Protection in relation to the project in question.

Please note that the type of fire retardant treatment recommended, i.e. NON-COM Exterior or DRICON, depends on the type of timber cladding to be used and, very importantly, whether a coating is to be applied. Timber cladding treated with DRICON can only be used externally when a coating is applied to the timber and this coating must be maintained throughout the life time of the timber.  If you require advice regarding the fire treatment most suitable to your specification/ timber type please contact us.

9.  Can you fire treat OSB board or MDF?
No - because of the composition of these products, they will tend to 'blow' or expand within the pressure treatment.

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10.  I want to fire treat a staircase. Which treatment should I be looking at?
DRICON is the most suitable treatment for staircases components, achieving Class 0 protection.  DRICON treated staircases have been assessed in the TF2000 fire test on a single timber staircase in a six storey building.  The detail of this is available from Chiltern International Fire.

11.  What will be the weight increase to fire retardant treated timbers/plywoods?
Typically fire retardant treatment adds around 12-15% to the weight of plywood and solid timber.

12.  What fire retardant treatments are suitable for use on the London Underground system?
DRICON is the only approved treatment for use on the London Underground system. Material needs to conform with Metronet/London Underground Standard 2-01001-002 Fire safety Performance of Materials Ref DPM-0735 July 2007. Treated material should be colour coded/hot branded to conform. 

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13. How does gluing affect treatment/treated timbers?
In general glued assemblies can be safely treated with either DRICON or NON-COM Exterior provide suitable waterproof glues have been used.  We do recommend that advice is sought from Arch before sending material for treatment.

When DRICON treated material is to be glued, again arch should be consulted.  Phenol formaldehyde, melamine formaldehyde or resorcinol types are generally recommended depending upon the end use. 

For NON-COM Exterior treated timbers, advice from Arch should always be sought if the timber is to be glued after treatment.

14.  Can I fire treat timbers to be used within indoor Swimming Pools facilities?
DRICON is the recommended treatment for timbers used in ceilings and claddings within the typically humid conditions of an indoor swimming pool facility.  A decorative coating may be applied on the treated timber, but we would recommend leaving the timber 'natural' as subsequent maintenance may prove difficult.

15.  How should waste treated timbers be disposed of?
Small off-cuts can be disposed of as industrial waste. Larger quantities of waste and redundant timber should be disposed of by a competent Waste Disposal Contractor.

Waste timbers should not be used for animal litter or bedding or fuel for barbeques or stoves.

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