Fire performance classes
Euroclass fire ratings for timber cladding explained
Euroclass is the European system for classifying how building products react to fire. It is set out in BS EN 13501-1 and is the system most commonly quoted for cladding in the UK today. This page explains it in plain English and shows where timber cladding sits.
It is general information to help you ask the right questions. The class you actually need depends on your building, so confirm it with Building Control or a fire engineer.
How to read a Euroclass
A rating such as B-s1,d0 has three parts. B is the main class, which describes how much the product contributes to a fire. s1 is the smoke production, and d0 means no flaming droplets or particles.
| Class | Typical meaning | Examples |
|---|---|---|
| A1 | No contribution to fire; non-combustible | Stone, brick, concrete, steel |
| A2-s1,d0 | Limited combustibility | Some mineral-based boards |
| B-s1,d0 | Very limited contribution | Fire retardant treated timber (certified systems) |
| C-s2,d0 | Limited contribution | Some treated timber and boards |
| D-s2,d0 | Acceptable contribution | Untreated timber cladding |
| E, F | Poor or untested | Not suitable for most external walls |
The smoke class runs from s1 (little smoke) to s3 (substantial smoke). The droplet class runs from d0 (no flaming droplets or particles within the test period) to d2 (substantial droplets). A1 and A2 are the only classes treated as non-combustible or of limited combustibility.
How the tests work
Timber and wood products are usually classified using the Single Burning Item (SBI) test, which measures how a corner assembly of the product contributes to a growing fire, together with a small flame test. The classification applies to the product tested in a specific end-use condition.
That is why two boards that look identical can have different classifications. Species, thickness, density, profile, joints, air gap and backing all matter, and so does the treatment and any finish applied on top.
Class 0 and Class 1: the older national classes
Before Euroclasses, UK specifications used national classes based on BS 476, such as Class 1 surface spread of flame and Class 0. You will still see these terms in older specifications, on some product data sheets and in conversations with clients. They are not the same test as BS EN 13501-1 and the two sets of classes do not convert directly.
If a specification asks for Class 0 or Class 1, ask the designer or Building Control which Euroclass, if any, they will accept, rather than assuming an equivalent. The current Approved Document B uses Euroclasses for most external wall requirements.
Untreated timber cladding
Under the European classification, most solid timber cladding of sufficient thickness and density is classed D-s2,d0 without further testing. That is adequate for many low-rise applications that are well away from boundaries, but it will not satisfy a requirement for Class B.
Why specify Class B-s1,d0?
- It is often required or recommended near boundaries, on taller buildings or on higher-risk building types.
- It gives more design freedom, allowing timber on projects that would otherwise need non-combustible cladding.
- Lower smoke production is better for escape routes and occupant safety.
- Some insurers and clients ask for it as a standard.
Class B is not a route around every restriction. In England, relevant buildings 18 m and above are subject to a ban on combustible materials in external walls, and treated timber is still combustible. See our building regulations page for the outline.
What to ask for
- The classification report or certificate (BS EN 13501-1).
- The tested end-use conditions: species, thickness, profile, air gap and substrate.
- Confirmation that any finish, paint or oil is covered by the certificate.
- Details on maintenance, re-treatment and expected service life.
Shop and specify
Frequently asked questions
Talk to our timber team
Tell us about your project and we will recommend the right species, profile, finish and fire performance. Free samples are available, and we can quote for bespoke milling.