- Maximum fire performance in timber: EuroClass B (B-s1-d0) — limited contribution to fire, minimal smoke, no burning droplets. Achieved by factory FR treatment with KUPRAFUNG flame retardant.
- Buildings over 18m: Standard timber cladding cannot be used as primary cladding material — Class A2-s1,d0 or better required under Approved Document B.
- Buildings 11–18m: External wall system assessment required under the Building Safety Act. EuroClass B timber appropriate subject to full EWS assessment.
- Buildings under 11m: No automatic requirement, but many commercial project specifications require EuroClass B as a minimum regardless.
- Available species: Siberian larch, ThermoWood, Nordic spruce — all available factory FR treated to EuroClass B.
- Certification: Full fire treatment certification provided with every order — not sourced retrospectively.
Fire rated timber cladding on commercial buildings is one of the most rapidly evolving areas of UK building specification — driven by the Building Safety Act 2022, the ongoing impact of the Grenfell inquiry on external wall system specification standards, and the tightening of local authority and client-side fire performance requirements on education, healthcare, and social housing projects. Getting the fire performance specification right on a commercial timber cladding project is not optional — it is the area where incorrect specification has the most serious consequences, and where the gap between what is specified and what is delivered most commonly creates problems. This guide covers the full fire performance picture for commercial timber cladding in the UK — what EuroClass B means, when it is required, how factory FR treatment works, what certification is needed, and what a completed fire-rated commercial timber cladding project looks like in practice.
Completed EuroClass B fire rated timber cladding at Oasis Academy Hadley, Enfield — Siberian larch factory FR treated to B-s1-d0 with KUPRAFUNG flame retardant, finished in Delta Hydrolasur grey, installed on a live 1,600-pupil school site in June 2025. This replaced fire-damaged cladding and delivered a higher fire performance standard than the original specification.
EuroClass Fire Classification — What the Letters and Numbers Mean
The EuroClass system (EN 13501-1) is the European standard — see also our fire rated cladding cost guide for commercial budget context for classifying the reaction to fire of construction products — it is the classification system specified in UK building regulations and commercial project specifications for external cladding. Understanding what the classification components mean is the starting point for any fire rated cladding specification:
| Classification | Main class | Smoke (s) | Burning droplets (d) | Meaning for timber cladding |
|---|---|---|---|---|
| A1-s1,d0 | Non-combustible | Minimal | None | Stone, concrete, steel — not timber |
| A2-s1,d0 | Limited combustibility | Minimal | None | Required for buildings over 18m — not achievable in timber |
| B-s1,d0 | Very limited contribution to fire | Minimal | None | Maximum achievable in FR treated timber — EuroClass B |
| C-s2,d0 | Limited contribution to fire | Medium | None | Achievable in some timber species untreated |
| D-s3,d0 | Acceptable contribution to fire | High | None | Standard untreated timber — most softwood species |
| E / F | High contribution / No performance determined | — | — | Not appropriate for external cladding on commercial buildings |
Buildings over 18m in height require external wall cladding systems to achieve Class A2-s1,d0 or better under Regulation 7 of the Building Regulations. Timber cladding — even factory FR treated to EuroClass B — cannot meet the A2 threshold and is therefore not appropriate as the primary cladding material on buildings over 18m. This is a hard regulatory limit, not a matter of specification preference. For buildings at or below 18m where EuroClass B is specified, factory FR treated timber cladding is the correct and compliant specification.
When Is Fire Rated Timber Cladding Required — Height and Sector Guide
| Building height | Regulatory requirement | Timber cladding position | Typical specification |
|---|---|---|---|
| Over 18m | A2-s1,d0 minimum under Reg 7 | Standard and FR timber NOT appropriate as primary cladding | Non-combustible alternatives required |
| 11–18m | EWS assessment required under Building Safety Act | FR treated timber appropriate subject to full wall build-up assessment | EuroClass B (B-s1,d0) FR treated timber |
| Under 11m — education | No automatic regulatory requirement | FR treated timber widely specified regardless | EuroClass B specified by most LA and academy trust clients |
| Under 11m — healthcare | No automatic regulatory requirement | FR treated timber frequently specified | EuroClass B specified by most NHS and private healthcare clients |
| Under 11m — social housing | No automatic regulatory requirement | FR treated timber increasingly specified | EuroClass B on higher-risk schemes; standard larch or ThermoWood on lower-risk |
| Under 11m — commercial / residential | No automatic regulatory requirement | FR treated timber where client specification requires | Standard naturally durable species unless client specifies otherwise |
How Factory FR Treatment Works — KUPRAFUNG and EuroClass B
Factory FR treatment is the process by which standard timber cladding boards are transformed into EuroClass B fire-rated cladding — and the word "factory" is important. Site-applied fire retardant products do not achieve the same penetration depth or consistency of coverage as factory-applied treatment, and do not carry the same EN 13501-1 test certification. For any commercial project where EuroClass B is specified, the treatment must be factory applied before boards are delivered to site.
Our fire rated timber cladding uses KUPRAFUNG flame retardant treatment — a proven commercially specified flame retardant applied by deep penetration in factory conditions. The process:
- Treatment depth: The flame retardant penetrates deep into the board structure, not just the surface layer — ensuring fire performance is maintained even if the board surface is cut, drilled, or abraded during installation
- All faces treated: Factory application treats all four faces of each board including the back face — critical because the hidden back face cannot be treated after installation, and an untreated back face undermines the fire performance of the whole board
- Certification: Each batch of FR treated boards is accompanied by KUPRAFUNG certification confirming the treatment specification and achieved EuroClass classification — B-s1,d0 under EN 13501-1
- Appearance: FR treatment has no visible effect on the appearance of the timber — boards look, install, and accept finishes identically to untreated boards. Grey stain, oiled finish, or any other colour treatment can be applied over FR treated boards
- Cut end re-treatment: Site-cut board ends must be re-treated with a compatible site-applied FR end grain sealer — we supply this with every FR treated order and specify the re-treatment requirement in our method statement
Fire Rated Timber Cladding — Available Species and Profiles
| Species | Natural durability | FR treatment available | FR classification | Best commercial application |
|---|---|---|---|---|
| Siberian Larch | Class 3 — no treatment required | Yes — KUPRAFUNG | EuroClass B (B-s1,d0) | Education, sport, healthcare, residential — most widely specified FR timber species |
| ThermoWood | Class 2 — zero maintenance | Yes — KUPRAFUNG | EuroClass B (B-s1,d0) | Social housing, healthcare, any project requiring maximum service life and zero maintenance alongside fire performance |
| Nordic Spruce | Class 4 — treatment required | Yes — KUPRAFUNG | EuroClass B (B-s1,d0) | Budget commercial where fire rating is required — note that standard durability treatment is still required alongside FR treatment on spruce |
All standard commercial profiles are available factory FR treated — see our cladding profiles guide for the full range. Shadow gap, double shadow gap, rainscreen, shiplap, tongue and groove, and feather edge in all three species. Bespoke profiles and pre-manufactured panel systems can also be FR treated before delivery — as demonstrated on the Oasis Academy Hadley project where FR treated panels were manufactured to drawing and installed by crane.
Fire Rated Cladding in Practice — Oasis Academy Hadley
Fire damage to the first and second floor cladding at Oasis Academy Hadley — caused by fireworks fired at the building in October 2024. The replacement specification was required to achieve EuroClass B (B-s1-d0) — a significant upgrade over the original cladding. TCS completed the supply, manufacture, and installation in June 2025.
Survey, manufacture drawings, bespoke board sizes to match existing facade, KUPRAFUNG FR treatment to B-s1-d0, Delta Hydrolasur grey finish, steel top-hat frame, pre-manufactured panels, crane installation on a live 1,600-pupil school. Full fire certification provided with the material.
Read full case studyFire Certification Documentation — What Is Required
Timber cladding on a commercial build — the full wall build-up, junction details, and fixing specification all form part of the EWS assessment documentation on buildings 11m and above. Fire-rated boards to EuroClass B are available across all standard commercial profiles.
On any commercial project where fire rated timber cladding is specified, the documentation requirement extends beyond the certification that comes with the boards. The full documentation picture for fire-rated commercial cladding:
- EN 13501-1 classification certificate: Confirming the specific timber species, treatment product, treatment specification, and achieved EuroClass classification — provided by TCS with every FR treated order
- KUPRAFUNG treatment certificate: Product-specific certificate confirming the flame retardant treatment applied, treatment depth, and achieved performance classification
- External Wall System (EWS) assessment: For buildings 11m and above, the full wall build-up — cladding, battens, insulation, membrane, structural substrate — must be assessed as a system, not just the cladding boards in isolation. TCS provides cladding data sheets and profile drawings for inclusion in the EWS assessment package — see our cladding detail drawings guide
- Cut end re-treatment specification: Method statement specifying the site-applied FR end grain sealer product and application method for all site-cut board ends — essential for maintaining fire performance across the installed cladding
- RAMS: Project-specific risk assessment and method statement covering FR treated board handling, cut end re-treatment protocol, and any additional controls specific to the site or building type
Specifying EuroClass B on the cladding boards but not addressing the full external wall system. EuroClass B is a classification for the boards in isolation — it is not a classification for the external wall as a whole. On buildings 11m and above, the full wall build-up must be assessed as a system under BR135 methodology. A EuroClass B board fixed over combustible insulation or a vapour permeable membrane without a full EWS assessment does not make a compliant external wall system. See our full Approved Document B timber cladding guide and EuroClass B guide for the complete compliance picture.
What is EuroClass B timber cladding?
EuroClass B (B-s1,d0) is the highest fire performance achievable in timber cladding — limited contribution to fire, minimal smoke production, no burning droplets. Achieved by factory FR treatment with KUPRAFUNG or similar flame retardant. Appropriate for commercial buildings under 18m where fire performance is specified.
When is fire rated timber cladding required on commercial buildings UK?
Buildings over 18m require A2-s1,d0 — timber cannot meet this. Buildings 11–18m require EWS assessment under the Building Safety Act. Many education, healthcare, and social housing projects specify EuroClass B regardless of height. Always confirm with building control and the fire consultant on each project.
How is fire rated timber cladding treated?
Factory application of KUPRAFUNG flame retardant by deep penetration — treating all board faces including the back face. Factory treatment achieves consistent depth and coverage that site-applied products cannot. Certification is issued per batch confirming EN 13501-1 EuroClass B classification.
Does fire treatment affect the appearance of timber cladding?
No — FR treatment has no visible effect on appearance, texture, or grain character. Boards look and install identically to untreated boards and accept all standard finishes including grey stain and clear UV oil. As demonstrated at Oasis Academy Hadley, FR treated larch can be colour finished to precisely match the surrounding untreated cladding.
Fire Rated Timber Cladding — EuroClass B Supply & Install
We supply and install factory FR treated timber cladding to EuroClass B (B-s1-d0). See our supply and install guide and commercial cladding guide for broader context in Siberian larch, ThermoWood, and Nordic spruce across all standard commercial profiles. Full fire certification, RAMS, and EWS documentation support provided. Contact our commercial team for budget pricing, technical submittals, or tender returns — 24–48 hour response.