Product comparison
Fiber Cement Board vs OSB
Fire class, moisture resistance, CE certification, and suitability for facades, fire-rated walls, and wet rooms — compared side by side.
Fire class
A1 vs Class D
Moisture
Cat. A (<1%) vs 15–25% swelling
Exterior facades
Fiber cement wins
Side-by-side comparison
| Property | OSB/3 | Fiber Cement Board (Terasun TSM) |
|---|---|---|
| Fire class | Class D (combustible) | ✓Class A1 (non-combustible) |
| Moisture behaviour | Swells 15–25% (EN 317) | ✓EN 12467 Category A — <1% swelling |
| Mould resistance | Susceptible (organic) | ✓Immune (inorganic, no food source) |
| Weight (12 mm) | ~10 kg/m² | 9.96 kg/m² (Terasun TSM) |
| CE marking | EN 300 | ✓EN 12467 — CE 1023-CPR-1565 P |
| European Technical Assessment | — | ✓ETA 24/0895 |
| Fire resistance (assembly) | Not tested / Class D | ✓E 120 / EI 90 / EW 120 |
| EPD (environmental) | Varies | ✓EPD-IES-0018268 (ISO 14025) |
| Exterior facade use | Conditional / limited | ✓Yes — all climates |
| Wet room use | Not recommended | ✓Yes — Category A |
| Cost | Lower material cost | Higher material cost |
Fire performance: the critical difference
OSB is classified as Class D — it contributes to fire and is classed as a combustible material. Standard and fire-retardant-treated OSB typically cannot achieve Class A2 required for facades on buildings above 18 m in most European member states.
Terasun TSM fiber cement board achieves Class A1 — non-combustible, with very limited smoke. The tested wall assembly reaches E 120 / EI 90 / EW 120, enabling use in fire-rated partitions and facades.
Moisture performance
OSB/3 has improved moisture resistance but remains a wood-based product. In ventilated facade systems it can be exposed to bulk water. Repeated wetting causes 15–25% thickness swelling (EN 317), edge delamination, and long-term strength loss. Organic content also means mould risk in persistently damp conditions.
Fiber cement board classified Category A under EN 12467 is dimensionally stable when fully saturated. Thickness swelling is less than 1%. There is no organic content, so mould cannot grow. This is the correct choice for Nordic, Atlantic, and Alpine climates where driving rain is frequent.
When OSB is appropriate
- • Internal sheathing in dry conditions
- • Structural bracing where Class D is acceptable
- • Roof decking under roofing membranes
- • Where cost is primary driver
- • Low-rise residential below 18 m
When fiber cement board is correct
- • Ventilated facade systems (all heights)
- • Buildings above 18 m (A2 required)
- • Fire-rated wall assemblies E120/EI90/EW120
- • Wet rooms and bathrooms
- • Steel frame and modular construction
- • Nordic, Atlantic, Alpine climates
- • LEED, BREEAM, DGNB projects
Frequently asked questions
Is fiber cement board better than OSB for facades?+
For ventilated facade systems, fiber cement board is technically superior. It is non-combustible (Class A1), dimensionally stable when wet (EN 12467 Category A), and immune to mould. OSB is combustible (Class D) and swells 15–25% when wetted — a significant risk in exposed exterior conditions.
Can OSB be used on exterior facades?+
OSB/3 can be used on protected exterior sheathing in some low-rise applications, but it is not recommended for ventilated facade systems exposed to rain, especially in northern European climates. Edge swelling and potential delamination are serious long-term risks.
Which is cheaper?+
OSB has a lower material cost per m². Fiber cement board costs more initially but requires no fire treatment, has a longer service life, and does not degrade when wet. Over 30–50 years, the total cost comparison often favours fiber cement board.