Choosing external wall insulation (EWI/ETICS) often comes down to two proven options: EPS (expanded polystyrene) or facade mineral wool. The right choice affects comfort, energy bills and long-term durability. Below is a practical, buyer-friendly comparison.
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At a glance
- 🔥 Fire safety: mineral wool is non-combustible (A1/A2); EPS is combustible and needs correct detailing.
- 🎧 Acoustics: mineral wool absorbs sound better — useful near busy roads.
- ❄️ Thermal performance: both can achieve low U-values — check λ-value and required thickness.
- 💨 Vapour diffusion: mineral wool is more vapour-open; EPS is more vapour-tight.
- 💸 Cost & speed: EPS is usually cheaper and faster to install; mineral wool tends to cost more and weigh more.
- 🛠️ System: always use a certified ETICS system (adhesive + board + fixings + base coat + mesh + render).
EPS (polystyrene) — popular, cost-effective
- ✅ Lower material cost and quick installation (light, easy to cut).
- ✅ Good thermal insulation at competitive thicknesses.
- ⚠️ Weaker acoustics than mineral wool.
- ⚠️ Combustible — requires correct fire-stopping and system components; follow local regulations and system guidance.
Where EPS often fits best: standard residential projects with tight budgets, low external noise, and no special fire constraints for the façade.
Facade mineral wool — safety & versatility
- ✅ Non-combustible (A1/A2) — excellent fire performance for façade zones.
- ✅ Better sound absorption — improves indoor acoustic comfort.
- ✅ Vapour-open — helps walls manage moisture; reduces risk of interstitial condensation (with proper design).
- ⚠️ Higher cost & weight than EPS; installation can take longer.
Where mineral wool often fits best: buildings with higher fire-safety expectations, louder locations, or where vapour openness is desired.
Quick comparison
| Criterion | EPS (polystyrene) | Mineral wool (facade) |
|---|---|---|
| Fire behaviour | 🔥 Combustible (needs correct detailing) | 🧯 Non-combustible (A1/A2) |
| Acoustics | 🎧 Basic | 🎧🎧 Better sound absorption |
| Vapour diffusion | 💨 Lower (more vapour-tight) | 💨 Higher (more vapour-open) |
| Weight | ⚖️ Very light | ⚖️ Heavier |
| Cost | 💸 Usually lower | 💸 Higher |
| Install speed | ⏱️ Fast / easy cutting | ⏱️ Slower, heavier boards |
Typical performance & thickness (guide)
- λ-values (declared):
- EPS façade boards: ~ 0.031–0.040 W/m·K
- Mineral wool façade boards: ~ 0.034–0.040 W/m·K
- Common thicknesses: 120–200 mm+ (depends on target U-value, wall type and climate).
Always design by U-value calculation and the chosen system certification.
Basic ETICS layers (do not mix brands)
- 🧱 Adhesive (and/or mechanical fixings) suitable for substrate.
- 🧩 Insulation boards (EPS or mineral wool), staggered joints.
- 🪪 Mechanical fixings per wind-load calculation and system guide.
- 🧵 Base coat + reinforcing mesh (alkali-resistant).
- 🎨 Primer + finish render (mineral/silicate/silicone/acrylic — system-approved).
- 🧰 Details: fire breaks (where required), drip edges, window reveals, plinths, movement joints, caps.
Tip: Pick a certified system from one manufacturer (e.g., Rockwool, Knauf, Isover, Ursa, etc.). Mixing components voids approvals and warranty.
When to choose what?
- Pick EPS if you need a budget-friendly, quick solution in a low-noise, low-risk fire scenario, with detailed design compliance.
- Pick mineral wool if fire safety, acoustic comfort or vapour openness are priorities — or when specification requires an A1/A2 façade.
Common mistakes to avoid
- 🚫 Using non-approved mixes of adhesives, mesh and renders.
- 🚫 Too few fixings or wrong types for the substrate/wind zone.
- 🚫 Skipping movement joints or incorrect plinth details.
- 🚫 Ignoring moisture paths at window sills, balconies and roof edges.
- 🚫 No plan for fire-stopping and compartmentation (where required).
Buying checklist
- ✅ Certified ETICS system (all layers from one brand).
- ✅ λ-value and thickness to reach the target U-value.
- ✅ Fire classification (A1/A2 for mineral wool; EPS with proper fire detailing).
- ✅ Acoustic need (busy road? choose mineral wool).
- ✅ Logistics: lead times, pallet sizes, access and offload (tail-lift/HIAB).
- ✅ Installation crew experienced with the chosen system.
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