September 14, 2026
As wood is increasingly specified for larger and more demanding projects, fire performance has become an important consideration alongside aesthetics, durability and structural integrity. This is especially true for public buildings such as cinemas, theatres, libraries, schools, offices, hotels and hospitals, where building regulations often require construction products to meet specific fire classifications.
Understanding the terminology, classifications and testing standards is essential when evaluating different solutions. This article explains what fire-retardant wood is, how its reaction to fire is classified according to European standards, and what Euroclass designations such as B-s1,d0 mean in practice.
Fire retardant wood is timber that has undergone a treatment designed to improve its reaction to fire.
As a result of the treatment, the fire behaviour of the wood is improved by:
It is important to distinguish fire retardant wood from non-combustible materials:
Even after treatment, wood remains a combustible material. Fire retardant systems are designed to improve how wood behaves when exposed to fire by slowing ignition and limiting fire growth, but they do not make wood non-combustible.
Different standards and classification systems are used around the world to assess the fire performance of construction products, including ASTM and NFPA standards in the United States, AS 1530 in Australia, and JIS standards in Japan. This article focuses on EN 13501-1, the European standard used to classify the reaction-to-fire performance of construction products under the Euroclass system*.
Under EN 13501-1, construction products are classified into Euroclasses ranging from A1 to F according to their reaction to fire. In general, the lower the class, the greater the material’s contribution to fire development.
*The Euroclass reaction-to-fire classification system is defined in Commission Delegated Regulation (EU) 2016/364. within the framework of the EU Construction Products Regulation (CPR)
| Euroclass | Description |
| A1 | Non-combustible |
| A2 | Very limited contribution to fire |
| B | Limited contribution to fire |
| C | Moderate contribution to fire |
| D | Higher contribution to fire |
| E | Easily flammable |
| F | No performance determined / highly flammable |
For architects, fire classifications provide a common language for comparing products. Rather than relying on marketing claims, decisions can be based on independently tested and classified fire performance.
These classifications are determined through standardised testing and assessment carried out by accredited laboratories. When specifying fire retardant wood, architects should therefore always verify the product’s declared Euroclass and supporting classification documentation to ensure it meets the requirements of the intended application.
The short answer is: up to Euroclass B
The longer answer is: Untreated solid wood cladding products are generally classified as Euroclass D under the European Commission’s Classification Without Further Testing (CWFT) provisions. However, fire-retardant treatment can significantly improve the reaction-to-fire performance of wood, allowing appropriately treated products to achieve up to Euroclass B.
However, it is important not to assume that every fire-retardant treated wood product automatically achieves the same classification. The declared Euroclass must always be supported by an official classification report based on standardised testing of the complete product.
A Euroclass designation such as B-s1,d0 consists of three separate performance indicators.
The first letter indicates how much the material contributes to fire growth.
Class B represents a limited contribution to fire growth compared with untreated combustible materials.
The smoke classification describes the amount of smoke generated during testing.
The droplet classification evaluates the production of flaming droplets or particles.
Together, B-s1,d0 indicates a material with limited contribution to fire growth, low smoke production and no flaming droplets under the conditions defined by the relevant European test methods.
Achieving the required Euroclass – whether this is Euroclass B or another classification – is only part of the picture.
The declared fire classification should always be considered in relation to the intended end use of the product. For exterior use, this also means considering whether the fire-retardant treatment maintains its performance after weather exposure. This is addressed by EN 16755, which specifies additional requirements for the durability of fire performance. We explain this in more detail in our guide to fire-retardant wood for exterior use.
→ Wood remains a combustible material, but with the appropriate fire retardant treatment it can achieve significantly improved reaction-to-fire performance. This enables the use of wood in many projects where compliance with specific fire performance requirements is essential.
→ Always verify the declared Euroclass and supporting classification documentation to ensure the product meets the requirements of your project.
Thermory offers fire-retardant wood solutions developed in cooperation with Woodsafe using the WOODSAFE® WFX system, helping architects and builders meet demanding fire performance requirements while retaining the natural appearance of wood.
Even after treatment, wood remains a combustible material and therefore cannot achieve Euroclass A1 or A2, which are reserved for non-combustible construction products such as concrete, brick and steel. For this reason, the highest reaction-to-fire classification wood can achieve is Euroclass B.
Architects should request the product’s Declaration of Performance (DoP) together with the official reaction-to-fire classification report confirming the declared Euroclass. For exterior applications, it is also important to verify documentation demonstrating the durability of the fire performance after weather exposure, such as testing in accordance with EN 16755, where applicable.
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