Failed cavity wall insulation: damp, your landlord, and what to do

Direct answer

Yes. If failed cavity wall insulation is letting damp penetrate the external walls of your rented home, putting it right is your landlord's responsibility for the structure of the property. Failed insulation can also be covered by the original installer's guarantee. Report the damp in writing, ask the landlord to investigate the cause, and keep photographs.

Cavity wall insulation (CWI) can fail, particularly older installations from the 1990s and 2000s, or installations that were not suitable for the type of property. When CWI fails, it can cause persistent damp penetration through external walls that is difficult to diagnose and hard to fix. If your landlord installed CWI that has failed, or owns a property where failed CWI is causing damp, they have an obligation to address it.

Key facts

• The 2024 to 2025 English Housing Survey found about 2% of homes in England had excess cold as a category 1 (most serious) hazard, rising to 3% of privately rented homes. Damp and cold getting in through failed insulation can contribute to this. English Housing Survey 2024-25, GOV.UK

What is cavity wall insulation and why does it fail?

External walls in many UK properties built between the 1930s and 1980s are cavity walls, two layers of brick or block with a gap (cavity) between them. Cavity wall insulation fills this gap with material (usually mineral wool, polystyrene beads, or foam) to improve energy efficiency.

CWI fails for several reasons:

• Wrong property type: properties exposed to severe driving rain, particularly those in coastal areas or on hillsides, are not suitable for CWI. Rain can saturate the insulation material, which then transfers moisture into the inner wall
• Blown or settled insulation: over time, insulation material can become compressed, creating cold bridges and gaps that allow moisture through
• Poorly installed insulation: gaps in installation, incorrect material, or installation that disturbs the weep holes (which allow drainage) can allow moisture to bridge the cavity
• Conversion of agricultural buildings: some properties were not originally designed for CWI and the installation caused problems from the outset

What are the signs of failed CWI?

• Damp patches on internal walls, particularly on walls that face the prevailing wind
• Damp that is spread across a large area of wall rather than being concentrated at a single point (unlike a localised leak)
• Damp that appears after periods of heavy rain
• Mould growth on external-facing walls
• Increased heating bills as the insulation loses effectiveness
• A diagnostic test by a specialist confirming water in the cavity

Who is responsible for failed CWI?

If the landlord installed the CWI, or if it was installed during the landlord's ownership, the landlord is responsible for addressing the consequences if it has failed. This is because:

• The landlord has an obligation to keep the structure and exterior in repair (Section 11, Landlord and Tenant Act 1985)
• Damp penetrating through external walls because of a structural defect is the landlord's responsibility
• The Homes (Fitness for Human Habitation) Act 2018 requires the property to be free from damp that is prejudicial to health

If the CWI was installed under a government scheme (such as the old Green Deal or ECO) and the installation was defective, the installer may also have liability, but this does not remove the landlord's duty to keep the property free from damp.

What should you do?

Step 1, Report the damp in writing: report the damp to your landlord, specifically noting that it appears on external walls and may be related to cavity wall insulation. Keep a copy of your report.

Step 2, Request investigation: ask the landlord to arrange for a specialist to investigate whether the CWI has failed. Some landlords resist this because remediation is expensive (CWI extraction can cost several thousand pounds).

Step 3, Contact environmental health: if the landlord will not act, the council's environmental health team can inspect the property and issue an Improvement Notice requiring the landlord to address the damp.

Step 4, Keep records: document the damp with photographs, temperature readings, and a diary of how it is affecting you and your household.

Can you bring a disrepair claim?

Yes. If failed CWI is causing damp in your home and your landlord has been informed but has not acted, this is actionable disrepair. A disrepair claim can include compensation for the period you have lived with the damp, as well as special damages for damaged belongings.

Failed CWI claims often require a surveyor's report to establish the cause of the damp, the surveyor will inspect the property and advise on whether CWI is responsible. This is usually arranged as part of the disrepair claim process.

When should I contact Support for Tenants?

If your home has persistent damp on external walls that your landlord will not investigate or fix, including where failed cavity wall insulation may be the cause, call us on 0800 030 4669.

No upfront cost. You only pay if you win, and the fee comes out of the compensation. If you don't win, you pay nothing.

Sources

• Landlord and Tenant Act 1985, Section 11 (legislation.gov.uk)
• Homes (Fitness for Human Habitation) Act 2018 (legislation.gov.uk)

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