How to Spot External Wall Insulation Damp Early: 10 Warning Signs
Early detection can save thousands. Recognize these signs before damage worsens.
Why External Wall Insulation Fails
External wall insulation (EWI) creates a waterproof barrier around your home. When properly installed and maintained, this protects the property. When it fails, it can trap moisture against your walls, leading to expensive damage.
The NAO found that 98% of ECO4 EWI installations will fail within 5 years. Recognizing early warning signs is critical to minimizing damage and costs.
The 10 Warning Signs
1. Dark Staining or Streaking on External Render
- Vertical dark streaks below windows or roof edges
- Discoloration around joints or seams
- Green or black algae growth on north-facing walls
Water is running down the surface instead of being shed properly. Indicates inadequate drip edges, poor detailing, or render breakdown.
Medium - Get inspected within 2 weeks
2. Cracks in Render or Basecoat
- Hairline cracks spreading in patterns
- Cracks wider than 2mm (credit card thickness)
- Cracks at corners, around windows, or at wall edges
- Spiderweb or map-like cracking patterns
Movement of insulation boards, thermal expansion/contraction, or poor adhesion. Cracks allow water ingress directly to the wall behind.
High - Get inspected within 1 week
3. Bubbling or Delamination
- Soft, spongy areas when you press the render
- Visible bulging or blistering
- Hollow sound when tapped gently
- Render coming away from insulation boards
Water has penetrated behind the render layer. The render is separating from the insulation boards. This rapidly worsens in freeze-thaw cycles.
Urgent - Get inspected within 48 hours
4. Internal Damp Patches
- Dark patches on inside walls, especially in corners
- Peeling wallpaper or paint
- Tide marks or salt deposits (white crystalline patches)
- Walls feel cold and clammy to touch
Moisture has penetrated through the EWI system and reached the internal wall. May indicate failed seals around windows, inadequate weatherproofing, or catastrophic system failure.
Urgent - Get inspected immediately
5. Mould Growth (Internal)
- Black, green, or brown spots or patches
- Musty smell, especially in corners or behind furniture
- Mould appearing after EWI installation (previously not present)
- Condensation on windows increasing since installation
EWI may have blocked ventilation paths or created cold bridges. Could also indicate interstitial condensation (moisture trapped within the wall structure).
High - Health risk. Get inspected within days
6. Blocked or Covered Airbricks
- Airbricks (ventilation grilles) covered by insulation
- Render extending below the damp proof course (DPC)
- No visible ventilation grilles at foundation level
Under-floor ventilation is blocked. This causes dampness in floors and walls, timber rot, and potential structural issues. This is a serious installation defect.
High - Structural risk. Get inspected within 1 week
7. Water Drips or Leaks After Rain
- Water dripping from render edges or soffits
- Damp spots appearing during or after rain
- Water pooling at the base of walls
- Internal leaks around window reveals
Water is penetrating the EWI system. Could indicate failed seals, inadequate drip edges, or gaps in the render. Water may be running behind the insulation.
Urgent - Immediate inspection required
8. Increased Condensation on Windows
- Heavy condensation appearing since EWI installation
- Water pooling on window sills
- Misting between double-glazing panes
EWI has changed the thermal properties of your home. May indicate inadequate ventilation design or thermal bridging at window reveals.
Medium - Monitor and get assessed within month
9. Sagging or Movement of Boards
- Visible "steps" or unevenness in the wall surface
- Boards appearing to slump or sag
- Gaps opening between boards
Insulation boards are not properly adhered to the wall. This is a critical installation failure. Boards may be secured with insufficient adhesive or wrong fixing method.
Urgent - Safety risk. Immediate inspection
10. Musty Odors
- Damp, musty smell that wasn't present before EWI
- Smell worse in certain rooms or corners
- Smell stronger after rain or in humid weather
Hidden moisture and mould growth within wall cavities. This can continue for months before visible signs appear. Indicates serious moisture penetration.
High - Get professional assessment ASAP
What to Do If You Spot Warning Signs
Immediate Actions
- Document everything: Take dated photos of all defects. Include close-ups and wide shots showing location.
- Note when it started: Record when you first noticed issues and whether they're getting worse.
- Check your paperwork: Find installation certificates, guarantees, and contractor details.
- Contact your installer: Report issues in writing immediately. Keep copies of all correspondence.
Get Professional Assessment
Don't wait for problems to worsen. Commission:
- Thermal imaging survey: Shows moisture penetration not yet visible (£200-£400)
- Moisture meter testing: Quantifies dampness levels (included in most surveys)
- Full structural survey: If significant defects found (£500-£1,200)
Report to Authorities
- Trustmark: If installer was Trustmark registered
- Trading Standards: If you suspect mis-selling or fraud
- Your local council: Environmental health may inspect
- Scheme administrator: If installed under ECO4 or GBIS
Prevention: What Good EWI Looks Like
Proper Installation Standards
- Boards mechanically fixed and adhesive bonded (not adhesive only)
- Continuous insulation with staggered joints
- Minimum 100mm clearance above ground level
- Proper sealing around all window and door reveals
- Drip edges installed at roof line and above windows
- Ventilation paths maintained (airbricks extended, not blocked)
- Render applied in correct weather conditions
- Adequate drying time between coats
Regular Maintenance
Even well-installed EWI requires maintenance:
- Annual visual inspection
- Clean algae/moss from render surface
- Check seals around windows annually
- Clear debris from drip edges
- Repoint any cracks within 3 months of appearance
Long-Term Outlook
If caught early, many EWI defects can be remedied without full removal:
- Minor cracks: £500-£2,000 to repair and seal
- Failed seals: £1,000-£5,000 to replace window/door detailing
- Partial delamination: £3,000-£10,000 for localized repair
- Complete failure: £15,000-£30,000 for full removal and replacement
Spotted Warning Signs?
Get a free initial assessment from independent surveyors who specialize in EWI failures. Early action saves thousands.
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