- Euroclass B-s1,d0 is the European fire classification most commonly required for external timber cladding on UK buildings over 11 metres — it covers flame spread, smoke, and flaming droplets.
- Class 0 is the older UK equivalent under BS 476 — broadly comparable to Euroclass B but not directly interchangeable and tested differently.
- Class 1 is a lower performance level for internal linings — it is not an acceptable substitute for Class 0 or Euroclass B on external walls.
- For most residential extensions under 11 metres and more than 1 metre from a boundary, no fire classification is required — standard timber cladding is acceptable.
- Factory pressure-impregnated treatment is the only reliable way to achieve a certified Euroclass B or Class 0 result — on-site application is not accepted by Building Control.
When fire rated cladding is specified on a UK building project, the paperwork that follows is often full of classifications, suffixes, and test standard references that mean very little without explanation. Euroclass B-s1,d0. Class 0 to BS 476. Reaction to fire. Limited combustibility. These terms appear on certificates, in specifications, and in Building Regulations guidance — and confusing one for another can result in non-compliant cladding reaching a building site.
This guide cuts through the terminology. It explains what each classification actually measures, how the European Euroclass system and the older UK Class system relate to each other, and which classification you need to specify for common building types in the UK. It is written for homeowners, architects, contractors, and developers who need a clear working understanding of fire performance requirements without reading the full text of Approved Document B.
Two Classification Systems — Why the UK Has Both
The UK currently operates with two fire classification systems running in parallel. This is a legacy of the transition from British Standards to European harmonised standards — a process that began in the 1990s and left both systems in active use across different parts of the construction industry.
The European fire classification system for construction products, introduced to create a single consistent testing framework across EU member states. Products are graded from A1 (non-combustible, highest performance) through to F (no performance determined, lowest). Each classification covers three measured properties: reaction to fire (letter grade), smoke production (s suffix), and flaming droplets (d suffix). The system remains in use in the UK post-Brexit.
The British Standards fire classification system, predating European harmonisation. Defines performance using Class 0, Class 1, Class 2, and Class 3 ratings based on surface spread of flame tests (BS 476 Part 7) and fire propagation (BS 476 Part 6). Still referenced in parts of Approved Document B, particularly for internal lining materials. Does not measure smoke production or flaming droplets separately.
For external timber cladding in the UK, the Euroclass system is now the primary framework. BS 476 classifications are still encountered on older specifications and for internal applications, but Euroclass is what Building Control and most fire engineers require on certification documentation for external walls.
Euroclass B, Class 0, and Class 1 — Side by Side
Class 1 and Class 0 are frequently confused. Class 1 is a lower performance level and cannot be used as a substitute for Class 0 on external walls. Similarly, listing "Class 1 or Euroclass B" as alternatives in a specification document is technically incorrect — they do not represent equivalent performance.
What Does B-s1,d0 Mean? The Full Breakdown
The full Euroclass designation for fire rated timber cladding is almost always written as B-s1,d0. Each component describes a different and independently tested aspect of the material's behaviour in a fire. All three must be present and certified for the classification to be valid.
A product certified as B-s1,d0 has been independently tested and confirmed to meet all three criteria simultaneously. When reviewing a fire certificate from a cladding supplier — including our own fire retardant treated cladding — check that all three components are stated, that the test standard EN 13501-1 is referenced, and that the certificate was issued by an accredited testing laboratory.
Factory fire treated ThermoWood cladding — certified to Euroclass B-s1,d0 — is visually identical to standard timber and installs using the same profiles and fixings.
Full Classification Comparison Table
| Classification | Test Standard | What It Measures | External Use | Buildings 11–18m |
|---|---|---|---|---|
| Euroclass A1 | EN 13501-1 | Non-combustible — no contribution to fire | Yes — highest performance | ✓ Required over 18m |
| Euroclass A2-s1,d0 | EN 13501-1 | Very limited combustibility, minimal smoke, no droplets | Yes | ✓ Required over 18m |
| Euroclass B-s1,d0 | EN 13501-1 | Limited flame spread, minimal smoke, no droplets | Yes — standard for 11–18m | ✓ Acceptable 11–18m |
| Euroclass C-s2,d0 | EN 13501-1 | Acceptable flame spread, moderate smoke | Limited — some low-rise | ✗ Not sufficient |
| Class 0 (BS 476) | BS 476 Parts 6 & 7 | Limited surface spread of flame and fire propagation | Yes — where BS 476 accepted | Confirm with Building Control |
| Class 1 (BS 476) | BS 476 Part 7 | Low surface spread of flame only | Not for fire rated external walls | ✗ Not sufficient |
| Untreated timber | — | No fire treatment — typically Euroclass D–E | Yes — where no fire rating required | ✗ Not acceptable |
Which Classification Does Your Project Need?
The requirement depends primarily on building height and use. Here is a practical guide to the most common UK residential and commercial project types:
| Project Type | Height | Classification Required | Notes |
|---|---|---|---|
| House extension | Under 11m, >1m from boundary | None — standard Siberian larch or ThermoWood acceptable | Check boundary rules first |
| House extension | Under 11m, within 1m of boundary | Euroclass B or Class 0 | Boundary elevation only |
| Residential building | 11–18m | Euroclass B-s1,d0 | All external wall elements |
| Residential building | Over 18m | Euroclass A2-s1,d0 minimum | Timber cladding not permitted |
| School or educational | Any | Euroclass B-s1,d0 | Confirm with fire engineer |
| Commercial / office | Any | Euroclass B-s1,d0 | Confirm with Building Control |
| Garden room / outbuilding | Single storey | Typically none | Confirm if habitable use |
For a full guide to when fire rated cladding is legally required on residential projects, see our detailed article on fire rated cladding for house extensions.
How to Read a Fire Certificate — What to Check
ThermoWood cladding on a UK residential project — supplied with full Euroclass B-s1,d0 fire certification when factory treated.
When a supplier provides fire certification documentation, check each of the following before accepting it as evidence of compliance:
- Test standard referenced — EN 13501-1 for Euroclass, or BS 476 Parts 6 and 7 for Class 0. If no test standard is stated the certificate is not valid.
- All three Euroclass components present — the certificate must state the reaction to fire class (B), the smoke suffix (s1), and the droplet suffix (d0). A certificate showing only "Class B" without suffixes is incomplete and should not be accepted.
- Accredited testing body — the certificate should reference testing at a UKAS-accredited laboratory or recognised European equivalent. Supplier self-certification without independent testing is not sufficient.
- Scope covers your exact product — confirm the certificate applies to the specific species, profile, and treatment system you are ordering. A certificate for ThermoWood shiplap does not automatically cover Nordic spruce tongue and groove.
- Treatment method stated — factory pressure-impregnation and on-site application are not equivalent. The certificate should specify how the treatment was applied.
All fire treated cladding supplied by Timber Cladding Specialists comes with full certification documentation covering species, profile, treatment system, test standard, and classification. If you need to present this to Building Control or a fire engineer, we provide it as standard with every order. Contact our team if you have specific documentation requirements for your project.
Factory Treatment vs On-Site Application
This is one of the most important practical points in fire rated cladding specification, and one that is frequently misunderstood on site.
A fire retardant treatment process carried out in a controlled factory environment using pressure vessels to force retardant solution deep into the cell structure of the timber. Produces a consistent, measurable, and certifiable penetration depth across every board. This is the treatment method used by Timber Cladding Specialists for all Euroclass B and Class 0 certified cladding.
On-site brush or spray application of fire retardant cannot replicate the penetration depth or consistency of factory pressure-impregnation. Coverage is variable, penetration is shallow, and the result cannot be independently verified or certified. In practice, Building Control will not accept on-site application as evidence of Euroclass B or Class 0 compliance under Approved Document B.
If fire rated Siberian larch cladding, Douglas fir cladding, or any other species is required for your project, always specify factory-treated boards. The additional lead time is minimal — typically no more than a few days on top of standard delivery — and the compliance certainty is significantly greater. See our factory coatings service for full details of available treatments.
When writing a cladding specification or tender document, always state the required classification in full — for example: "Euroclass B-s1,d0 to EN 13501-1, factory pressure-treated, with full certification documentation provided at point of supply." This removes ambiguity and ensures every supplier quoting responds with a genuinely compliant product.
Euroclass B (B-s1,d0) is a European fire classification tested to EN 13501-1, covering flame spread, smoke production, and flaming droplets. Class 0 is a UK classification under BS 476 Parts 6 and 7 covering surface spread of flame and fire propagation. The two systems are broadly comparable in performance level but are not directly interchangeable. Your Building Control officer or fire engineer should confirm which is acceptable for your specific project.
Yes. For buildings between 11 and 18 metres in height, Euroclass B-s1,d0 is the standard required for external cladding under Approved Document B (2022 edition). For residential buildings over 18 metres, the requirement increases to Euroclass A2-s1,d0 or better. Timber cladding — even with factory fire treatment — cannot achieve A2 classification and is therefore not permitted on buildings over 18 metres.
B-s1,d0 is the full Euroclass fire classification for the most commonly specified fire rated timber cladding. B indicates limited combustibility (reaction to fire class). s1 indicates minimal smoke production. d0 indicates no flaming droplets or particles are produced. All three components must be tested and certified together under EN 13501-1 for the classification to be valid.
No — not where fire rated cladding is required. Class 1 under BS 476 Part 7 is a lower performance level primarily intended for internal wall and ceiling linings. Where fire rated external cladding is required under Building Regulations, Class 0 or Euroclass B-s1,d0 is the appropriate specification. Class 1 used in place of Class 0 on an external wall would not satisfy Approved Document B and would likely fail Building Control inspection.
It depends on the treatment type. Factory pressure-impregnated treatments penetrate deeply through the full cross-section of the board and are more tolerant of site cutting, though re-treatment of cut ends remains best practice. Surface-applied or shallow-penetration systems should always have cut ends re-treated on site. Your supplier should provide specific guidance — always request this documentation as part of your order.
Fire Rated Timber Cladding — Certified to Euroclass B-s1,d0 & UK Class 0
Timber Cladding Specialists supply factory fire-treated timber cladding with full certification documentation, across all main species and profiles. Available in ThermoWood, Siberian larch, Douglas fir, and Nordic spruce. FSC and PEFC certified. Nationwide delivery in 7–14 days.