10 Signs of External Wall Insulation Failure
External wall insulation (EWI) failures are often subtle at first but rapidly escalate. Learn to recognize the early warning signs before minor problems become expensive disasters requiring full system removal.
Quick EWI Failure Checklist
Check your property for these signs. Even ONE indicates potential EWI failure:
Detailed Warning Signs Explained
Render Cracking
Cracks in the render surface are the most common early sign of EWI failure. Not all cracks are equal - pattern and location reveal the cause.
Types of cracks:
- Horizontal cracks: Usually at joints between insulation boards. Indicates poor installation (no staggered joints).
- Diagonal cracks from corners: Stress cracks from thermal movement. Missing or inadequate expansion joints.
- Spider web pattern: Render applied too thick or wrong mix ratio. Surface will fail catastrophically.
- Vertical cracks at windows: No mesh reinforcement at openings. Water will penetrate.
Timeline: Cracks often appear within 1-3 years of installation. If your EWI is cracking already, it was poorly installed.
Bulging or Delamination
The render system separating from the insulation boards beneath. Creates a hollow sound when tapped. Rain penetrates behind the render, accelerating failure.
What causes delamination:
- • Inadequate bonding between base coat and insulation
- • Wrong adhesive used for the substrate type
- • Installation in wet conditions (adhesive didn't cure properly)
- • No mechanical fixings (relying on adhesive alone)
- • Thermal expansion/contraction cycles
Test: Gently tap the render with knuckles. Solid sound = good adhesion. Hollow sound = delamination.
Biological Growth (Algae, Moss, Mould)
Green or black organic growth on the render surface. While some growth is normal on north-facing walls, excessive coverage indicates moisture retention problems.
Why it grows:
- • Non-breathable render traps moisture at surface
- • Missing anti-biological agents in render mix
- • Poor drainage - water sits on surface instead of shedding
- • Render too porous (wrong sand grade used)
- • North-facing walls never dry out
Significance: Growth itself isn't structural damage, but indicates the render stays wet - leading to freeze/thaw damage in winter.
Water Penetration After Rain
Damp patches appearing on internal walls within hours or days of heavy rain. This is penetrating damp - water is getting through the EWI system.
Common entry points:
- • Window/door reveals (no drip edges or sealant failure)
- • Cracks in render (even hairline cracks allow water in)
- • Poor flashing at roof junctions
- • Behind wall-mounted fixtures (satellite dishes, lights)
- • Bottom edge of EWI (missing starter track allows wicking)
Critical: Once water enters, it's trapped between the original wall and insulation. Leads to interstitial condensation and hidden damage.
Interior Mould Growth
Black mould appearing on internal walls, especially in room corners, behind furniture, or around window reveals. Often starts within 6-18 months of EWI installation.
Why EWI causes interior mould:
- • Reduced breathability - moisture vapor can't escape
- • Cold bridging at poorly insulated junctions
- • Penetrating damp from failed render
- • No ventilation upgrade when breathability was reduced
- • Interstitial condensation creating permanently damp walls
Health risk: Black mould (Stachybotrys) causes respiratory problems. Particularly dangerous for children, elderly, and those with asthma.
Render Falling Off
Sections of render detaching and falling away from the wall. This is advanced failure - the entire system is likely compromised and will need replacement or removal.
Causes of catastrophic failure:
- • Freeze/thaw cycles - water in cracks expands when frozen
- • Complete adhesive failure (wrong adhesive or application)
- • Wind loading on delaminated sections
- • Mesh not embedded properly - no structural integrity
- • Substrate movement (wall ties corroding, bricks spalling)
Danger: Falling render can injure people or damage property. Contact a specialist immediately if render is detaching.
Staining and Discoloration
Water streaks, rust stains, or dark patches on the render. Indicates water is running down the face (poor drainage) or rust from fixings is bleeding through.
Types of staining:
- Dark streaks from gutters/windows: Poor drip details
- Rust stains: Fixings corroding behind render
- Efflorescence (white salt): Moisture bringing salts from brick
- Dark patches at board joints: Differential moisture absorption
Poor Detailing at Junctions
Visible gaps, cracks, or poor finishes where EWI meets windows, doors, rooflines, or ground level. These areas are most vulnerable to water ingress.
Critical junction points:
- • Window reveals - should have drip beads, often missing
- • Roof/wall junction - flashing must overlap EWI correctly
- • Ground level - starter track and stop bead essential
- • Internal/external corners - mesh wrapping required
No Visible Expansion Joints
Expansion joints allow thermal movement. Without them, render cracks as it expands/contracts with temperature. Joints should be visible every 3-6 meters.
If you can't see expansion joints on your EWI: The system will crack. It's just a matter of when. Thermal movement in direct sunlight can be 20mm+ on a large wall.
Rapid Deterioration (Less Than 5 Years Old)
Properly installed EWI should last 25+ years. If your system is already failing within 5 years, it was installed incorrectly and will only get worse.
Government scheme failures:
ECO4 and GBIS installations have particularly high failure rates (98% according to the NAO Report). Rushed installations, wrong materials, and inadequate oversight mean these systems often fail within 1-3 years.
What to Do If You Spot These Signs
Step 1: Get a Professional Survey
Don't try to diagnose or fix EWI problems yourself. A RICS-certified surveyor can assess the extent of failure, identify root causes, and advise whether repair or removal is needed. Cost: £350-£600.
Book EWI SurveyStep 2: Document Everything
Take dated photos of all defects. Note when symptoms appeared. Keep all installation paperwork, guarantees, and correspondence. This evidence is essential for compensation claims.
Step 3: Contact Installer (If Still Trading)
Send written notice of defects, requesting remediation. If they installed under warranty, they're obligated to fix problems. Many installers have ceased trading to avoid this - don't be surprised if they ignore you.
Step 4: Explore Compensation Options
If you have a CIGA guarantee, Trustmark certificate, or the work was under ECO4/GBIS, you may be entitled to compensation. Specialist solicitors work no-win-no-fee to recover removal and repair costs.
Learn About ClaimsSpotted EWI Failure Signs?
Get a professional assessment, repair quotes, and compensation claims support. Act now before minor problems become expensive emergencies.