EPS vs Mineral Wool: ETICS

PS (Polystyrene) vs. Mineral Wool (Basalt Wool) ETICS

What’s the difference, and which should you choose for your façade insulation?

Quick summary

• Thermal performance: Similar at the same thickness (both meet modern U-values when designed correctly).
• Fire safety: Mineral Wool (MW) is non-combustible; EPS is combustible but safe in certified systems with proper detailing and fire barriers.
• Acoustics: MW generally absorbs sound better than EPS.
• Moisture & breathability: MW is more vapor-open; EPS is more vapor-resistant (can help against wind-driven rain but needs careful vapor management).
• Weight & handling: MW is heavier and stiffer; EPS is lighter and faster to install.
• Upfront costs (percentages only): See the cost section below—MW is typically higher than EPS.

What they are

• EPS (Polystyrene) ETICS: Insulation boards (expanded polystyrene) adhesively fixed and/or mechanically anchored to the exterior wall, reinforced mesh, base coat, and decorative finish.
• Mineral Wool (Basalt) ETICS: Similar build-up, but with mineral wool boards (typically rock/basalt wool) that are non-combustible and more vapor-permeable.

Advantages & disadvantages

EPS (Polystyrene)

Pros

• Lighter boards → faster installation and easier handling.
• Stable thermal performance and excellent value at a given U-value.
• Good resistance to intermittent wetting when rendered correctly.

Cons

• Combustible; requires certified system components, correct render thickness, and fire breaks around openings/floor lines.
• Less vapor-open; requires careful design on walls that need to dry outward.
• Weaker acoustic absorption than MW.
• Can shrink slightly over time if poorly specified/installed (mitigated by proper brand/system and detailing).

Best fit

• Standard residential buildings where speed and budget matter, with compliant fire detailing and a certified ETICS system.

Mineral Wool (Basalt Wool)

Pros

• Non-combustible (Euroclass A1) → superior façade fire performance.
• Vapor-open; helps walls dry outward (useful on solid masonry or mixed substrates).
• Better acoustic performance; helps reduce airborne noise.
• High dimensional stability under temperature changes.

Cons

• Heavier and stiffer → longer install time and more fixings.
• Needs careful weather protection during installation (fibrous edges can take on water if left exposed pre-render).
• Upfront cost is higher than EPS.

Best fit

• Projects with fire-safety priority (multi-storey, escape routes per local code), acoustic goals, or where vapor openness is desired.

Performance notes (non-price)

• Thermal: At the same thickness, EPS and MW can achieve similar U-values; choose thickness by heat-loss calculations, not by material myths.
• Fire: MW is non-combustible; EPS systems rely on system certification, render layers, and horizontal/vertical fire barriers for compliance—especially at floor slabs and around windows/doors.
• Acoustic: MW typically improves façade sound absorption versus EPS in comparable assemblies.
• Moisture: MW allows more outward drying; EPS reduces vapor flow and can be helpful in wet climates if interior vapor control is correct.
• Impact & durability: Both depend mainly on the reinforcement mesh grade, basecoat thickness, and finish. Use high-impact mesh at ground floors and corners.

Cost guide (percentages only; EPS = baseline 0%)

(Actual percentages vary by country, system brand, thickness, building height, access, and façade complexity.)

• Materials (boards + adhesives + mesh + finish)
  • Mineral Wool vs. EPS: +20–50%
• Fixings & accessories (anchors, around openings, fire breaks)
  • Mineral Wool vs. EPS: +5–15% (more/stronger fixings typically required)
• Labor & installation time
  • Mineral Wool vs. EPS: +10–25% (heavier boards, tighter tolerances)
• Scaffolding/Access (for the same façade)
  • Mineral Wool vs. EPS: +0–10% (install duration impact)
• Lifecycle & maintenance (render refresh, sealants)
  • Mineral Wool vs. EPS: typically 0–5% difference over the first maintenance cycle when both are specified and installed correctly; main driver is finish quality and exposure, not the board type.

Benefits (owner outcomes)

• Energy savings: Comparable when designed to the same U-value; correct thickness and airtightness deliver most of the gain.
• Comfort: Warmer interior surfaces, fewer cold spots, and reduced condensation risk on both systems.
• Noise: Noticeable improvement with MW on noisy streets or near busy areas.
• Compliance & insurance: MW can simplify fire approvals for certain building types; EPS remains acceptable where permitted by code with correct fire detailing.

Key risks & how to avoid them

• Wrong system pairing (any material): Always use a single, certified ETICS system (boards + adhesives + mesh + base + finish from one manufacturer).
• Fire detailing (EPS): Omit fire barriers and you increase risk—specify mineral wool fire breaks at floor lines and openings where required.
• Moisture traps (EPS): Pair with appropriate interior vapor control; avoid sandwiching moisture between low-permeance layers.
• Water ingress during install (MW): Protect boards from rain before render; follow the weather window guidance.
• Impact damage at ground level (both): Use high-impact mesh and/or protective claddings/plinth finishes.
• Poor adhesion/substrate prep (both): Clean, sound substrate; correct rasping/levelling; correct anchor pattern by wind-zone calculations.

When to choose which

• Choose EPS if your project prioritizes speed and lower upfront cost, within a code-compliant fire strategy, and the wall build-up doesn’t require high vapor openness.
• Choose Mineral Wool if your priorities are fire safety, better acoustics, and vapor openness, and you accept a higher upfront cost with slightly longer installation.

FAQ (short)

• Is Mineral Wool always more energy-efficient than EPS? No. For the same U-value and detailing, energy performance is comparable.
• Can I mix EPS and Mineral Wool? Yes, in designed fire breaks or specific zones, but only within a certified system and per manufacturer details.
• Does Mineral Wool get wet? The fibers are hydrophobic, but boards can hold surface water; protect during install and render promptly.
• How thick do I need to go? Determined by heat-loss calculations and code; thickness, not the brand, drives the U-value.