- Treatment cost: Fire retardant treatment costs approximately £29.99 per m² — added to the standard board cost.
- Siberian larch fire treated: approximately £75–£95 per m² (board cost + £29.99 treatment).
- ThermoWood fire treated: approximately £85–£125 per m² (board cost + £29.99 treatment).
- Nordic spruce fire treated: approximately £50–£72 per m² (board cost + £29.99 treatment).
- Lead time: 2–3 weeks — order well ahead of programme. Standard boards ship in 7–14 days.
- What you get: Euroclass B-s1,d0 reaction to fire classification with full test certificates for building control submission.
- When required: Residential buildings over 11m (fire-engineered approach), buildings close to boundaries, and some commercial projects where the fire engineer specifies it.
Fire rated timber cladding — boards that have received factory-applied fire retardant treatment to achieve Euroclass B-s1,d0 reaction to fire classification — is increasingly specified on UK residential and commercial projects following post-Grenfell changes to Building Regulations. The cost premium over standard untreated cladding is real but quantifiable, and the specification process is straightforward when engaged at the right stage of the project. This guide gives architects, developers, and specifiers clear pricing, lead times, and specification guidance for fire treated timber cladding in the UK in 2026.
What Is Fire Rated Timber Cladding?
Fire rated timber cladding is standard exterior cladding that has received factory-applied fire retardant impregnation treatment, upgrading its reaction to fire classification from the standard Euroclass D (normal combustible timber) to Euroclass B-s1,d0 or better. The treatment is a pressure impregnation process applied in a controlled factory environment — salts or other fire retardant compounds are forced deep into the timber under pressure, bonding with the wood fibres and significantly altering the material's behaviour when exposed to fire.
The result is a cladding board that looks and installs identically to an untreated board but performs significantly better in a fire scenario — limiting flame spread across the surface, reducing heat release rate, and minimising smoke production and flaming droplet formation. Full test certificates from an accredited laboratory are produced for every treatment batch and supplied with the order for building control submission.
It is important to distinguish fire retardant treatment from fire resistant construction. A fire rated cladding board achieves a specific reaction to fire classification — how the material behaves when exposed to fire. This is separate from fire resistance — how long a construction element maintains its structural integrity under fire conditions. Timber cladding boards are reaction to fire products, not fire resistance products. Both are relevant to building regulations compliance but they address different aspects of fire performance. For full guidance on how UK building regulations apply to timber cladding see our timber cladding building regulations guide and our self build cladding guide. Browse our fire rated cladding range for currently stocked treated profiles.
Euroclass B-s1,d0 reaction to fire classification for timber cladding can only be achieved through factory pressure impregnation treatment — not through site-applied intumescent paints or coatings alone. Site-applied products may achieve Class 1 or Class 0 under the superseded national classification system, but cannot achieve the Euroclass B classification required for building control submission under current UK regulations. Always specify factory-treated boards with accredited test certificates.
When Is Fire Rated Cladding Required?
- Regulation 7(2) combustibility prohibition applies
- Fire-engineered alternative approach needed
- Euroclass B-s1,d0 minimum for alternative approach
- Fire engineer must be engaged at design stage
- Building control agreement required before ordering
- Tight unprotected area calculations
- Fire engineer may specify treated cladding
- Reduces unprotected area contribution of cladding
- Particularly relevant for urban infill plots
- Confirm with building control at design stage
- Not subject to Reg 7(2) combustibility ban
- Fire engineer may specify for risk management
- Some planning conditions specify fire performance
- Insurance or client requirements may drive spec
- Confirm with fire engineer for specific project
- Reg 7(2) does not apply below 11m
- Standard untreated cladding acceptable
- Subject to boundary distance rules only
- Most UK houses, extensions, and garden rooms
- Confirm with building control if close to boundary
For the full regulatory framework governing fire performance of external cladding — including the 11m threshold, unprotected area calculations, and boundary distance rules — see our Approved Document B and timber cladding guide.
Euroclass B-s1,d0 — What It Means and What It Costs
The Euroclass reaction to fire system replaced the previous UK national classification (Class 0, Class 1, Class 2, Class 3) following the 2025 amendments to Approved Document B. All building control submissions in England now reference Euroclass ratings. The classifications relevant to fire treated timber cladding are:
| Euroclass | Flame spread | Smoke (s) | Droplets (d) | For timber cladding |
|---|---|---|---|---|
| A1 | Non-combustible | — | — | Not achievable for timber |
| A2-s1,d0 | Non-combustible | Very limited | None | Not achievable for timber |
| B-s1,d0 | Very limited | Very limited | None | Best achievable for treated timber — target classification |
| C-s2,d0 | Limited | Limited | None | Achievable — lower than B, less accepted |
| D | Normal contribution | S2 | d0 | Untreated timber — standard classification |
Fire Rated Cladding Cost by Species — UK 2026
| Species / profile | Untreated cost/m² | Treatment cost/m² | Fire treated total/m² |
|---|---|---|---|
| Siberian Larch — feather edge / shiplap | £35–£55 | £29.99 | £65–£85 |
| Siberian Larch — shadow gap | £45–£65 | £29.99 | £75–£95 |
| Siberian Larch — rainscreen | £45–£65 | £29.99 | £75–£95 |
| ThermoWood — shiplap / feather edge | £55–£75 | £29.99 | £85–£105 |
| ThermoWood — shadow gap | £60–£80 | £29.99 | £90–£110 |
| ThermoWood — triple shadow gap | £75–£95 | £29.99 | £105–£125 |
| Nordic Spruce — shiplap / shadow gap | £22–£38 | £29.99 | £52–£68 |
The fire retardant treatment cost of £29.99 per m² is a fixed charge regardless of species or profile. On a 200m² commercial project in Siberian larch shadow gap, that is £5,998 in treatment cost — significant, but modest relative to total project value and the cost of non-compliance. Treatment is priced transparently — the board cost plus £29.99 per m² gives the total fire treated material cost for any species or profile. Contact our team at design stage to confirm specification, lead times (2–3 weeks), and total cost before committing to programme dates.
Project Cost Examples — Fire Treated vs Standard
| Project type | Area | Species / profile | Standard cost | Fire treated cost |
|---|---|---|---|---|
| House extension | 40m² | Larch shadow gap | £1,800–£2,600 | £3,000–£3,800 (+£1,200 treatment) |
| 3-storey residential | 120m² | Larch shadow gap | £5,400–£7,800 | £9,000–£11,400 (+£3,600 treatment) |
| 4-storey block of flats | 300m² | ThermoWood shadow gap | £18,000–£24,000 | £27,000–£33,000 (+£9,000 treatment) |
| Commercial office | 200m² | Larch rainscreen | £9,000–£13,000 | £15,000–£19,000 (+£6,000 treatment) |
All figures are materials only. Add £10–£15 per m² for battens, membrane, and fixings, and £25–£45 per m² for installation labour. For a full materials and installed cost breakdown see our timber cladding cost per m² guide.
How to Specify Fire Rated Timber Cladding — Step by Step
- Confirm the requirement with building control or fire engineer at design stage — determine whether Euroclass B-s1,d0 is required for your specific project and whether a fire-engineered alternative approach has been agreed for residential buildings over 11m
- Select species and profile — fire treatment is available across Siberian larch, ThermoWood, and Nordic spruce in most standard profiles. Confirm profile availability when requesting a quotation as not all profiles are stocked pre-treated
- Request a quotation early — include species, profile, dimensions, quantity, and required Euroclass. We will confirm availability, treatment lead time, cost, and documentation
- Order with sufficient lead time — allow 2–3 weeks from order to delivery. Factor this into your construction programme. Late specification of fire treatment is the most common cause of programme delay on projects where it is required
- Receive test certificates with delivery — all fire treated boards are supplied with EN 13823 test certificates for building control submission. Keep these on file — building control will request them at inspection
- Install correctly — fire treated boards install identically to untreated boards. Use A4 stainless steel fixings throughout. Do not cut treated boards on site without sealing cut ends with the supplied end grain treatment product
Factory fire retardant treatment penetrates the timber but does not protect cut ends made on site. Every cut end — at junctions, openings, and board lengths — must be sealed with the supplied end grain treatment product before installation. Unsealed cut ends are a compliance gap and may invalidate the test certificate for building control purposes. We supply end grain treatment solution with every fire treated cladding order.
NBS Specification Language — Fire Rated Timber Cladding
For architects writing NBS clauses for fire treated timber cladding, the correct specification language is:
- Timber species: Siberian larch (Larix sibirica) — naturally durable, Durability Class 3 (BS EN 350)
- Fire retardant treatment: Factory pressure impregnation — Euroclass B-s1,d0 reaction to fire (EN 13823 / EN ISO 11925-2)
- Profile: [specify profile and dimensions]
- Certification: EN 13823 test certificate from UKAS accredited laboratory — supplied with delivery
- Supplier: EMI Interiors Ltd t/a Timber Cladding Specialists, March, Cambridgeshire
- Installation: Ventilated rainscreen system — minimum 25mm clear cavity, breather membrane to substrate, A4 stainless steel fixings throughout, cut ends sealed with supplied end grain treatment
- Certification: FSC and PEFC certified — certificates available on request
For our full fire retardant treatment service details including available species, profiles, treatment certifications, and NBS product data for building control submission, contact our technical team. We also offer a factory coatings service — fire treated boards can be pre-coated at the factory in your specified colour, eliminating the need for on-site coating of treated boards. See also our Euroclass B, Class 0 and Class 1 cladding guide and our fire rated cladding for house extensions guide.
How much does fire rated timber cladding cost in the UK?
Fire rated timber cladding achieving Euroclass B-s1,d0 costs approximately 15–25% more than untreated equivalent boards. Fire treated Siberian larch shadow gap costs approximately £54–£81 per m² versus £45–£65 per m² untreated. Fire treated ThermoWood shadow gap costs approximately £72–£100 per m² versus £60–£80 per m² untreated. Full test certificates are included with every order.
When is fire rated cladding required in the UK?
Fire rated cladding is most commonly required for residential buildings with a storey at 11m or more (where a fire-engineered alternative approach to the Regulation 7(2) combustibility prohibition is being pursued), buildings close to boundaries where unprotected area calculations are tight, and commercial projects where the fire engineer specifies improved fire performance. Most houses, extensions, and garden rooms below 11m do not require fire treated cladding.
What does Euroclass B-s1,d0 mean for timber cladding?
Euroclass B-s1,d0 means: B — very limited flame spread contribution to fire; s1 — very limited smoke production; d0 — no flaming droplets or particles. It is achieved through factory pressure impregnation treatment — not site-applied coatings. It is the best reaction to fire classification achievable for timber cladding and the classification most commonly specified for fire-engineered alternative approach submissions.
Does fire rated cladding look different from untreated cladding?
No — factory pressure impregnation treatment does not alter the appearance, colour, or surface texture of the boards. Fire treated Siberian larch and ThermoWood look identical to untreated equivalents once installed. Some surface salt migration can occur shortly after treatment but dissipates naturally before or during installation.
How long does fire rated cladding take to deliver?
Fire retardant treated timber cladding typically requires 2–3 weeks from order to delivery. Standard untreated profiles ship in 7–14 days from UK stock. Specify and order fire treated boards at design stage — not when the contractor arrives on site. Late specification is the most common cause of programme delay on fire-rated cladding projects.
Fire Rated Timber Cladding — Euroclass B-s1,d0 with Full Test Certificates
We supply fire retardant treated timber cladding in Siberian larch, ThermoWood, and Nordic spruce achieving Euroclass B-s1,d0. Full EN 13823 test certificates supplied with every order for building control submission. NBS product data available. Contact our technical team with your project details for a quotation and lead time confirmation.