🔥 Poorly Built Cladding
If the exterior wall is clad with unsuitable or poorly built thermal cladding, the fire will melt the thin external render and find the bare EPS.
Fire Protection in External Insulation (ETICS): How to Prevent the Building Envelope Becoming a Torch Relay
External thermal insulation (thermal cladding) is the best investment you can make to cut your electricity and heating bills. In essence, you "dress" the building in a thick jacket, usually made of Expanded Polystyrene (EPS).
However, as we've seen, EPS is combustible. What happens if a rubbish bin catches fire next to the wall? Or, even worse, what happens if a flat on the 1st floor catches fire and the flames burst out of the window, "licking" the façade?
1. The Terrifying "Chimney Effect"
When a flame exits through a window, it tends to move upwards, clinging to the exterior wall.
⚡ Explosive Spread
At that point, the fire finds abundant "fuel." The EPS ignites and fire begins racing vertically up the façade at terrifying speed.
🏢 Floor-to-Floor Spread
Within minutes, the fire reaches the 2nd-floor window, shatters the glass and enters the next flat. This is called the "Chimney Effect" and is the reason many multi-storey buildings have been completely destroyed.
2. The Shield of External Insulation: It's Not Just the Polystyrene!
To prevent this, we must understand that external insulation is not a single material - it is a SYSTEM (ETICS). Your safety doesn't depend only on the insulation material, but on the "armour" that hides it.
1️⃣ Base Coat (The Adhesive)
Over the insulation, a layer of special, cementitious material is applied.
2️⃣ Glass Mesh (The Net)
Inside the base coat, a durable glass-fibre mesh is "encased."
3️⃣ Final Render
The decorative finish we see on the outside.
🛡️ The Triple Armour
This "sandwich" (3–5 mm thick) is your only defence! If built correctly, it starves the EPS of oxygen. When fire strikes the wall, the EPS behind may heat up and shrink slightly, but because it has no oxygen and is protected by the non-combustible render, it does not ignite.
3. The Crime of "Frankenstein" Materials
The biggest mistake in Greece is "marrying" unrelated materials to reduce cost.
❌ The Cheap Build
The contractor buys EPS from factory A, cheap tile adhesive from factory B (instead of certified base coat) and a random mesh. This is not an ETICS system. It is a "Frankenstein" experiment.
🔥 In a Fire
In a fire, the cheap adhesive will crack immediately. The mesh will melt. The fire will enter the insulation and the house will go up in flames.
✅ Certified ETICS
A Certified ETICS System (with CE marking) has been tested in laboratories as a complete assembly and guarantees that the render won't tear and won't let the fire reach the EPS.
The Experiment in Our Model (The Balcony Fire in the 4×4)
We're having a barbecue on the balcony. The grill catches fire and the flames (1.5 metres tall) lick the external wall that has EPS thermal cladding.
❌ Scenario A (The "Frankenstein" System)
The builder had installed a "cheap and cheerful" mix of materials, applying a very thin render (just 1 millimetre) to finish quickly. At 3 minutes, the thin render cracks from the heat. The polystyrene is exposed. It ignites. In 10 minutes the fire has burned the entire façade and climbed onto the roof. Destruction.
✅ Scenario B (The Certified ETICS System)
We paid a little extra for a branded, certified system with a thick, elastic and non-combustible base coat. The grill's flames "scorch" the wall. The final render blackens, but doesn't crack! The glass mesh holds the armour together. The EPS behind it gets no oxygen. We extinguish the grill. The wall just has a black mark that needs repainting. The defence worked perfectly!
Final Takeaway: If you choose polystyrene (EPS) for your thermal cladding, don't skimp on its "armour." Demand a strictly certified and branded ETICS system from your contractor. The thick, properly reinforced render is what will keep fire away from your insulation.
Related Articles
PIR & Polyurethane (PUR): The Truth About Foam Insulation in Fire and Charring Fire Barriers: Why We Install Rock Wool Strips Between EPS Insulation on Tall Buildings Insulation Combustibility Guide: Euroclass A1 to F Crash Test: EPS (Polystyrene) vs Rock Wool in Fire
Fire Protection: Passive Safety & Building Protection
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