Seven warning signs that your cavity wall insulation may have failed — and what each one means for your property.
Cavity wall insulation, when installed correctly in a suitable property, should last for decades without problems. But a significant number of installations — particularly those carried out under government-funded programmes in the 2000s and 2010s — have failed, often because the property was incorrectly assessed as suitable.
Failed insulation doesn't always make itself obvious immediately. The signs can develop gradually over months or years. Here's what to look for.
If you're experiencing any of these signs and cavity wall insulation was installed in your property, contact us to arrange a borescope cavity survey. This is the only definitive way to confirm what's happening inside the cavity.
The most obvious sign. If you notice damp patches — particularly on external-facing walls — especially after rain, this strongly suggests moisture is being conducted through the cavity by the insulation. The patches may be visible as discolouration, tide marks or actual wet areas.
If insulation has slumped, voided or degraded, areas of wall that should feel warm now feel cold to the touch. This is a sign of uneven coverage or loss of insulation value. You may notice particular cold areas in corners or lower down walls where slumped material has left gaps above.
Mould thrives where there is moisture and warmth. If failed insulation is keeping walls persistently damp, mould will establish itself — typically in corners, near floor level on external walls, or around window reveals. Black mould is a health risk and should be treated as urgent.
Moisture in the wall migrates through to the inner surface, causing wallpaper adhesive to fail and paint to bubble, blister or flake. This often appears first on ground-floor walls and at lower levels where damp is most concentrated.
Wet insulation and the mould it supports produce a characteristic musty smell. If you notice this smell — particularly in rooms with external walls — even when you can't see obvious damp, it may indicate insulation problems within the wall cavity.
Failed insulation reduces thermal performance and saturated insulation can actively conduct heat outward. If your bills haven't improved — or have worsened — since insulation was installed, the insulation may not be performing or may have failed.
Persistent damp and mould affect indoor air quality. If household members — particularly children or those with asthma — experience worsening respiratory symptoms at home, this is a serious signal that damp and mould should be investigated and addressed.
The right first step is a borescope cavity survey. A camera is inserted through small holes drilled in the wall to inspect the cavity directly. This confirms:
You'll receive a written report detailing findings. If extraction is needed, this report supports a complaint against the original installer or a claim through CIGA (Cavity Insulation Guarantee Agency) or your insurer.
Zest can inspect the cavity and advise whether the insulation can remain, requires remedial work or should be extracted.
