Cavity Wall Insulation Problems, Signs of Failure and How to Fix It

What is Cavity Wall Insulation?

Most houses built in England and Wales after around 1920 have cavity walls, two parallel layers of brick with a gap between them. Cavity wall insulation (CWI) fills that gap with mineral wool, polystyrene beads, or foam to reduce heat loss.

When CWI is correctly installed in a suitable property, it is one of the most cost-effective energy improvements available. The Energy Saving Trust estimates it can reduce heating bills by a meaningful amount. It is also one of the most significant improvements an assessor can recommend on an EPC certificate.

The problem is that CWI is not suitable for every property, and millions of homes received free installations under government schemes without adequate exposure assessment. As a result, a significant number of homes across the UK have CWI that is failing, damp, or causing structural problems.

Signs of Cavity Wall Insulation Failure

If your home has CWI, or you suspect a previous owner had it installed, watch for the following:

• **Cold, damp walls**, Internal walls that feel cold and wet, particularly during winter, despite the property being heated
• **Mould growth**, Mould appearing on interior wall surfaces, especially in corners and on external walls
• **Staining on brickwork**, Tide marks or salt staining on external brickwork indicating water movement through the wall
• **Increased condensation**, Noticeably worse condensation on windows and cold surfaces
• **Unexplained rise in heating costs**, If energy bills have risen despite no change in usage, insulation failure may be the cause

Why CWI Fails

Getting a CWI Assessment

If you suspect failure, the first step is to commission a specialist survey. A qualified surveyor can use borescope cameras, thin cameras inserted through small drill holes, to inspect the cavity condition without significant disruption. The British Board of Agrément (BBA) and the Cavity Insulation Guarantee Agency (CIGA) both maintain guidance on surveying standards.

Under the PAS 2035 standard, any retrofit measure, including CWI installation, must be assessed and designed by a qualified Retrofit Assessor before work begins. If your CWI was installed without this assessment and problems have followed, this may support a complaint against the installer.

Removal and Remediation

Failed CWI can be extracted by drilling additional holes in the outer brickwork and using high-powered vacuum equipment to remove the material. This is a specialist process and should only be carried out by a TrustMark-registered contractor.

After extraction, the wall ties should be inspected and replaced if corroded. The brickwork will then need repointing if holes are visible. In some cases, an alternative insulation approach, such as internal wall insulation, may be recommended instead of re-filling the cavity.

Impact on Your EPC

An EPC assessor records wall construction and insulation status as part of the assessment. A property with failed or absent CWI will score lower than one with effective insulation. Correcting a CWI problem and having a new EPC issued can meaningfully improve your rating.

You can check the current EPC recommendation for your property, including whether CWI is listed as a suggested improvement, by searching your address on Property Passport UK, which displays live EPC data for every UK address.

Making a Complaint

If your CWI was installed under a government-backed scheme such as ECO or the now-closed Green Deal, and it has caused damp or damage, you may be eligible for remediation at no cost. Contact CIGA in the first instance, and if the installing company is no longer trading, the scheme administrator may still be liable.