Key Changes to Fire Safety of CWFT (Classified Without Further Testing) Timber Cladding: What Specifiers Must Know

The fire classification landscape for timber products has evolved and the implications for treated, modified, or coated variants of cladding are significant. While untreated solid timber meeting specific density and thickness criteria has historically been eligible for CWFT (Classified Without Further Testing) and assumed to achieve Euroclass D-s2,d0, this no longer applies to treated or modified wood products following recent regulatory changes. 

The EU Commission Delegated Regulation C(2023)7486, which narrows the scope of CWFT and closes a critical loophole by becoming an instrument that dictates how the standard EN14915 must be applied in relation to a specific product characteristic (reaction to fire) and a specific type of product (treated/modified wood).

(EU) CWFT Update (Effective August 2024):
The CWFT (Classified Without Further Testing) table has been amended to apply only to untreated wood.

• This means modified timbers, including thermally treated, impregnated, and coated products are no longer eligible for automatic Euroclass D,s2-d0 classification.
• These products now require full fire testing and classification under EN 13501-1 by an accredited 3rd Party.
• Reliance on the general "wood is D" assumption is no longer sufficient for modified or treated products.
• A key point in the regulation is that all wood products, whether treated or untreated, must, at a minimum, meet the D-s2, d0 (or D,s2-d2 in certain criteria) classification for fire safety, and this has to be proven through testing.

This is now EU law and must be adopted in all EU member states (and Northern Ireland).

Why this matters:
Coated timber, often used to enhance aesthetics or durability, is now treated as a modified product under CWFT. This ensures that surface treatments are properly assessed for their impact on fire performance.

This update closes a long-standing misinterpretation of CWFT applicability. It should raise the bar for fire safety and ensure that any modifications to timbers are properly assessed for their real-world performance. It is important to understand that the minor amendment to the CWFT was required to clear up misinterpretation, and never intended to include any modification to timbers. It is clear that any modification to timber will have an effect on the fire classification.

This EU legislation has not yet been adopted in the UK, so is there a point of nuance in UK building regulations? 

While with traditional domestic dwellings below 11 meters and more than 1 meter from a boundary, there isn't a specific Euroclass requirement like A2-s1,d0 or B-s1,d0 for external timber cladding, the CWFT (Classification Without Further Testing) change for modified timbers still has a significant practical impact. In the UK we still work from the previous CWFT table stating ‘wood pieces’ with a minimum density and thickness used in various end-use conditions should achieve D-s2,d0 classification.

Here's why, even without an explicit Euroclass reaction to fire mandate:

It is common knowledge that the treatment of timber in any way will have a direct implication to the fire classification. Even when timber cladding is used in a situation when UK Approved Document B regulations state ‘No provisions’ required regarding fire classification, the timber should still achieve minimum Euroclass D-s2-d0. The ‘No provisions’ wording should not be taken as any timber product could be applied in any situation as there are clear guidelines even with current CWFT instructions as long as not misinterpreted.

• "Adequately Resists" and Duty of Care:
  • Approved Document B, Requirement B4, broadly states that "The external walls of the building shall adequately resist the spread of fire over the walls and from one building to another..."
  • Even without a specific Euroclass, UK Building Control, whether a local authority or an Approved Inspector, has a duty to ensure this requirement is met.
  • Before the CWFT change, it was generally assumed that timber would meet this "adequate resistance" for this building type and distance, often aligning with a D-s2,d0 performance implicitly.
    
    
• No More "Free Pass" for Modified, Coated or Treated Timber:
  • The core of the (EU) CWFT change is that the assumption of a D-s2,d0 classification no longer applies to modified, treated or coated timber without test evidence.
  • This means if you're specifying timber claddings, you can no longer simply state "it's Euroclass D" based on old CWFT tables for untreated timber in the EU (and Northern Ireland).
    
    
• The Need for Evidence:
  • Now, for any modified, coated or treated timber, you should be able to provide evidence that it performs at least to the level of untreated timber (i.e., D-s2,d0) in its end-use application.
  • This evidence will come in the form of a Euroclass classification report to EN 13501-1, based on testing (e.g., SBI test to EN 13823).
  • While the regulation might not require a B or C classification, it now requires the D classification (or better) to be demonstrated by test results for these modified products.
    
    
• Implications for Designers, Specifiers, and Manufacturers:
  • Manufacturers: Should now have a direct responsibility to ensure their modified/treated or coated timber cladding products are tested and correctly classified. They can no longer just assume or declare D-s2,d0 without evidence.
  • Architects/Designers: May need to be more diligent in asking for and reviewing Euroclass classification reports for any modified, coated or treated timber cladding. They should confirm the manufacturer has the necessary test data for its reaction to fire in the intended application.
  • Building Control/Approved Inspectors: Should increasingly ask for these classification reports for modified/treated timber, even on lower-risk (no provision) dwellings, to ensure the "adequate resistance" requirement of B4 is genuinely met.
    
    
• Risk Mitigation and Best Practice:
  • Even if not strictly mandated by a Euroclass classification in UK Building Regs for this specific scenario, choosing timber with a known, tested reaction to fire performance (even if it's "just" D-s2,d0) must be deemed a crucial part of demonstrating due diligence and meeting the Approved Document B part B4 safety requirements.
  • Many designers might still opt for fire-retardant treated timber (aiming for Euroclass C or B) in situations where there's a higher perceived risk, even if not strictly required by regulation height/boundary rules, to provide an additional layer of safety and peace of mind. The (EU) CWFT change simply means that if you do use treated/modified/coated timbers, its performance must be evidenced by testing.

While the target classification for these lower-risk domestic dwellings hasn't changed to a higher Euroclass, the method of proving compliance for modified or treated timber has. The assumption of CWFT for anything other than truly untreated wood has been removed, placing a greater burden on manufacturers and specifiers to provide actual test data.

Read more:
New EUROPEAN COMMISSION Regulation Enhances Fire Safety Standard for Wood Panelling, Cladding AND RIBBONS

Nordtreat is driving the future of fire-retardant timbers by pioneering non-toxic, bio-based flame retardant technologies that combine high performance with environmental certifications, setting a new benchmark for sustainable fire protection, with proven test evidence across various timber cladding substrates and real-world scenarios, from Euroclass D to B.

Let’s keep pushing for safer, smarter, and more sustainable timber solutions.

Writer: 

Craig Lovatt
Regional Sales Manager, UK 
Nordtreat Oy

+44 7471 948 275
craig.lovatt[@]nordtreat.com