Fibre cement is a composite made from Portland cement, cellulose fibre, and fine aggregate — it looks like timber or a smooth render panel but behaves like a mineral board. It does not burn, does not rot, does not swell with moisture, and resists insect attack. For those reasons it has become the default choice on residential and commercial projects where the fire performance of a rainscreen is a design or regulatory requirement.
This guide covers the main board formats, how they are fixed, what they cost, and where they sit against the alternatives.
Board and Plank Formats
Fibre cement comes in three practical shapes for external cladding in the UK:
Planks (lapped cladding) — horizontal boards mimicking timber weatherboarding, typically 180–300 mm exposed face and 6–8 mm thick. Laid with a 25–30 mm lap, they give a domestic appearance and are common on new-build housing and timber-frame extensions.
Flat sheets/panels — large format boards (1,200 × 2,400 mm or 3,000 mm lengths) 8–12 mm thick, used as rainscreen cassettes or in a secret-fixed grid. They suit contemporary architecture with flush, linear or large-format aesthetics.
Soffit and fascia boards — thinner sheets (6 mm) rated for sheltered locations; moisture resistance is still required even in soffits.
All formats are factory-primed. Most manufacturers supply pre-coloured or factory-painted boards with 10–15 year paint guarantees; site painting with appropriate masonry or exterior acrylic coatings is also possible.
Fire Classification
Under the Construction Products Regulation and the UK Building Regulations (England — Approved Document B, 2022 edition), external wall cladding products on buildings above 11 m must meet a minimum reaction-to-fire class of A2-s1,d0 (limited combustibility). Fibre cement boards from established manufacturers consistently achieve A2-s1,d0 to BS EN 13501-1, placing them in the limited-combustibility category alongside brick, concrete, and mineral wool.
This makes fibre cement one of the few cladding products that is unrestricted on high-rise buildings without additional fire engineering justification — a significant factor after the post-Grenfell regulatory tightening that ruled out standard timber, many aluminium composites, and expanded polystyrene render in high-rise applications.
On buildings under 11 m there is no mandatory fire class for cladding, but specifiers on housing association and social housing schemes typically require A2 or Class B minimum regardless of height.
Lifespan and Maintenance
Service life for fibre cement boards in the UK climate is generally quoted at 30–50 years with appropriate maintenance. Unlike timber, the substrate does not require periodic treatment against rot or insect attack. However the factory paint coat will need refreshing approximately every 10–15 years depending on orientation and exposure zone.
Boards should be kept clear of standing water at joints and base of wall — the cellulose fibre reinforcement can absorb moisture if cut edges are not sealed. Cut edges on site must be sealed with the manufacturer’s edge primer before fixing.
Fixing Methods
Concealed/Secret Fixed (Flat Sheet)
A purpose-made aluminium secret-fix clip system attached to a vertical carrier grid. No face fixings are visible. This is the standard rainscreen approach on commercial or contemporary residential projects and requires the boards to be factory-drilled or routed. Carrier grids are typically 50 × 50 mm aluminium hat section at 400–600 mm centres.
Face Fixed (Planks)
Stainless steel ring-shank nails or stainless screws, typically 50 × 2.8 mm, at 400 mm centres into vertical treated softwood battens (minimum 38 × 50 mm). Nail heads are countersunk and filled with colour-matched jointing compound. This is the standard approach for lapped plank systems on timber-frame housing.
Battens must be fixed to a structural substrate capable of transferring wind loads — typically 18 mm OSB, structural ply, or masonry. The cavity behind the boards (minimum 25 mm) must be ventilated at the base and top of the wall and drained at base flashings to BS 8297:2017 (rainscreen cladding) and the NHBC Standards Chapter 6.9.
Cost
| Format | Supply only | Installed (typical range) |
|---|---|---|
| Lapped planks (180 mm face) | £12–£22/m² | £35–£55/m² |
| Large-format flat sheets | £18–£35/m² | £45–£70/m² |
| Soffit boards (6 mm) | £8–£14/m² | £25–£40/m² |
Installed costs include battens, fixings, primer/paint, and labour. Scaffolding, cavity barriers, intumescent seals, and design fees are additional. On multi-storey buildings where BS 8414 fire testing or a BBA Certificate is required for the complete system, specification costs rise accordingly.
Fibre Cement vs Timber vs Render — Key Comparison
| Property | Fibre cement | Timber cladding | Through-colour render |
|---|---|---|---|
| Fire class | A2-s1,d0 | Class D (untreated) | A1–A2 depending on system |
| Rot risk | None | Moderate–high if untreated | None |
| Maintenance cycle | Paint ~15 yrs | Stain/oil 3–7 yrs | Crack repairs as needed |
| Installed cost | £35–£70/m² | £40–£80/m² (hardwood) | £55–£90/m² (EWI system) |
| Appearance | Timber look or flat panel | Natural grain | Seamless, contemporary |
| Planning (conservation) | Generally acceptable | Usually preferred | Often refused on heritage |
| High-rise permitted | Yes (≥A2) | No (under 11 m only) | Depends on insulant |
Installation Standards and Compliance
Key references for fibre cement cladding installations in the UK:
- Approved Document B (England, 2022) — external wall fire performance thresholds at 11 m and 18 m
- Approved Document C — weather resistance; the rainscreen must manage driving rain to exposure zone requirements (BS 8104)
- BS 8297:2017 — code of practice for rainscreen cladding design and installation
- NHBC Standards Chapter 6.9 — cladding on new homes
- BS EN 12467 — product standard for fibre cement flat sheets (classifies boards by durability category 1–3 and reaction-to-fire)
- Individual manufacturer BBA Certificates or ETA for specific systems
Always use the manufacturer’s recommended fixing and joint detail. Mixed-brand systems (boards from one supplier, clips from another) can invalidate fire classification and warranty.
Practical Notes for Specifiers
Fibre cement boards are heavy relative to timber — large-format 12 mm sheets at 1,200 × 2,400 mm can weigh 45–55 kg per sheet. This requires appropriate lifting equipment on site and means the carrier bracket/grid loading must be checked in structural calculations.
Thermal bridging through metal carrier brackets should be accounted for in SAP/SBEM calculations; proprietary thermal break clips are available for better-performing fabric specifications.
On projects where planning requires a brick or stone appearance, brick-slip panels bonded to fibre cement substrates are an approved method that combines the dimensional stability of fibre cement with a masonry aesthetic — see the companion guide on brick slips for detail.
