What B-s1,d0 means for wood: fire class explained
B-s1,d0 explained simply: B = very limited contribution to fire, s1 = little smoke, d0 = no burning droplets. What it means for timber and how to achieve it.
EN 13501-1 test results and certified scope explained for fire-retardant wood.
By Priit Jänes, Products and Innovation, Solid Protect OÜ · Updated September 2026
If you are specifying fire-retardant wood for a building project, B-s1,d0 will appear in technical documents, permit requirements, and product datasheets. This article explains what the classification means, what the EN 13501-1 test numbers show, and how to check whether the classification applies to your product and project conditions.
01What is EN 13501-1 and why does it matter?
EN 13501-1:2018 is the European standard for classifying construction products according to their reaction-to-fire performance. It applies to products used in walls, ceilings, façades, linings, and other building applications. It does not replace fire-resistance classifications such as R, REI, or load-bearing fire design. The standard defines seven reaction-to-fire classes: A1, A2, B, C, D, E, and F. Class A1 covers non-combustible materials such as mineral wool and concrete. Class B is the highest Euroclass commonly achievable for exposed fire-retardant-treated wood, below the A1 and A2 classes used for non-combustible or near-non-combustible materials. For typical untreated softwoods used in cladding and lining applications, class B is generally not achieved without fire-retardant treatment. A properly applied and tested fire-retardant system can bring typical softwoods into class B, provided the treatment and installation conditions are covered by valid certification documents.
02Breaking down B-s1,d0
B - reaction to fire
The letter B describes how the material behaves when directly exposed to flame and radiant heat. The primary test method is EN 13823 (the Single Burning Item test, or SBI), where a corner configuration of two panels is exposed to a 30 kW burner at the base for 21 minutes. Key measured parameters: FIGRA (Fire Growth Rate index, must be below 120 W/s for class B), THR600s (Total Heat Release in 600 seconds, must be below 7.5 MJ), and LFS (flame must not reach the specimen edges). A secondary test, EN ISO 11925-2 (direct flame ignition for 30 seconds), confirms no sustained flame spread.
s1 - smoke production
The suffix s1 is the strictest smoke class. SMOGRA must be below 30 m2/s2, and TSP600s must be below 50 m2. Class s2 allows up to SMOGRA 180 m2/s2 - six times more smoke growth. Dense smoke reduces visibility and causes inhalation injuries well before flames reach an area.
d0 - flaming droplets and particles
The suffix d0 means no flaming droplets or particles were produced during the test within 600 seconds. Flaming droplets are a secondary ignition hazard - a single droplet landing on a combustible surface can start a new fire front.
03SPFR100 as an example: B-s1,d0 test results
SPFR100 was tested on solid spruce panels (18 mm and 50 mm thickness) treated with two coats at a total application rate of 240 g/m2. Tests were carried out by SIA “Meža un koksnes produktu pētniecības un attīstības institūts” / Forest and Wood Products Research and Development Institute, Latvia, accredited under LVS EN ISO/IEC 17025 (T-316), Notified Body NB 2040 under EU CPR 305/2011. Classification report number: K16/2024.
| Parameter | Measured value | Class B limit | Result |
|---|---|---|---|
| FIGRA 0.2MJ | 56.1 W/s | 120 W/s | Pass |
| FIGRA 0.4MJ | 51.8 W/s | 120 W/s | Pass |
| THR600s | 4.4 MJ | 7.5 MJ | Pass |
| LFS | Did not reach edge | No edge spread | Pass |
| SMOGRA | 2.8 m2/s2 | 30 m2/s2 | Pass (s1) |
| TSP600s | 24.3 m2 | 50 m2 | Pass (s1) |
| Flaming droplets | None | None within 600s | Pass (d0) |
| EN ISO 11925-2 | Flame spread compliant | Fs compliant | Pass |
The FIGRA value of 56.1 W/s is less than half the class B threshold of 120 W/s. The SMOGRA of 2.8 m²/s² is less than one tenth of the s1 limit of 30 m²/s². These are not borderline results. The values show SPFR100's performance in the tested and certified configuration, while project-specific use should always be matched with the relevant documentation. The certificate of conformity ET-0388-24 was first issued by Inspecta Estonia OÜ, part of Kiwa, on 14 February 2024 and remains valid until 13 February 2029, provided the technical description, manufacturing conditions, and factory production control are not significantly modified.
04How B-s1,d0 compares to adjacent classes
| Class | Typical materials | FIGRA limit | THR limit |
|---|---|---|---|
| A1 | Concrete, mineral wool, steel | Non-combustible | - |
| A2 | Fire-resistant boards | 120 W/s | 7.5 MJ |
| B | Fire-retardant treated wood | 120 W/s | 7.5 MJ |
| C | Some dense hardwoods | 250 W/s | 15 MJ |
| D | Untreated softwood, OSB | 750 W/s | 50 MJ |
| E | Untreated thin boards | Ignition only | - |
05When B-s1,d0 is required by regulation
B-s1,d0 or better may be required for exterior façade cladding, escape routes, stairwells, corridors, public buildings, and certain mass timber applications. The exact requirement depends on the national building code, building height, use class, and occupancy.
Practical checklist for B-s1,d0 wood products
Before specifying or installing any B-s1,d0 classified wood product, confirm that the classification applies to the exact product and project conditions.
- Check the required reaction-to-fire classification
Confirm the required reaction-to-fire class under the relevant national building code and project fire strategy. - Verify the classification report or certificate
Make sure the product has a valid EN 13501-1 classification report or certificate from an accredited body. - Check the field of application
Review whether the classification covers the intended wood species, board thickness, substrate, air gap, orientation, fastening method, and end-use condition. - Match the tested system
The classification applies only to the tested system. Changes in coating, treatment rate, substrate, timber type, or installation method may affect validity. - Follow the manufacturer’s application instructions
Use the declared consumption rate, number of coats, drying time, curing conditions, and maintenance procedure. - Avoid untested coatings or modifications
Do not apply additional paints, oils, lacquers, or topcoats unless they are included in the tested system or approved by the manufacturer. - Keep documentation on file
Store certificates, classification reports, datasheets, and application records as part of the building’s fire safety documentation.
06Specification text you can copy
Use this as a starting point for the fire section of your specification or tender documents. Adjust the element and class to your project’s fire strategy.
Reaction to fire: external timber cladding shall achieve class B-s1,d0 in accordance with EN 13501-1. Fire-retardant treatment by impregnation, applied at the rate and number of coats stated in the manufacturer’s classification report. Before installation, the contractor shall submit: (1) an EN 13501-1 classification report and certificate covering the specified timber species, thickness and build-up; (2) the technical data sheet; (3) a treatment record stating product, batch, quantity applied (g/m²), number of coats and date. No additional coatings shall be applied unless they are included in the classified system or approved by the manufacturer.
07Frequently asked questions
Does SPFR100 give every timber class B-s1,d0?
No. SPFR100 reaches B-s1,d0 in the certified configuration described in classification report K16/2024. On other species, thicknesses and build-ups, the achievable class depends on the timber and the solution, and should be verified for the project.
How much SPFR100 is needed?
The certified total application is 240 g/m² (approximately 210 ml/m²), in at least two coats. Planed surfaces usually need three coats to take up the full amount.
Can I apply oil, paint or a topcoat over SPFR100?
Only if it is included in the tested system or approved by the manufacturer. If you need a color, SPFR100 can be tinted, so fire protection and tone come from the same product.
Which documents should I ask for?
The EN 13501-1 certificate (ET-0388-24), the classification report (K16/2024), the technical data sheet, the safety data sheet and a treatment record with quantity and coats. All SPFR100 documents are on the Documents page.
Can the treatment be done in the factory?
Yes. SPFR100 can be applied by brush, spray, dipping or industrial treatment, including autoclave. Factory treatment makes it easier to control the application rate and document it.
08Summary
B-s1,d0 is a high reaction-to-fire classification for combustible timber products. SPFR100's published test results for the certified spruce configuration meet the class B, s1 and d0 criteria under EN 13501-1. Other wood species, substrates and configurations require project-specific verification. For any fire-retardant wood product, always confirm that the required classification, substrate, and installation conditions are covered by the relevant project documentation.
Priit Jänes is responsible for products and innovation at Solid Protect OÜ. Solid Protect develops and produces fire-retardant treatments for wood at its facility in Tänassilma, Estonia, and holds KIWA certification ET-0388-24 for SPFR100 under EN 13501-1:2018.
References: EN 13501-1:2018; EN 13823:2020+A1:2022; EN ISO 11925-2:2020, as used in classification report K16/2024; Classification report K16/2024 (SIA MKPPI, Latvia); KIWA certificate ET-0388-24 (Inspecta Estonia OÜ, 14.02.2024).
See the full SPFR100 specification and certified scope →
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