Cavity Wall Insulation Claim Calculator UK 2026/27
Estimate a claim for failed insulation causing damp & mould - extraction, repairs and damages
Last updated: June 2026
Cavity wall insulation claims explained
Millions of UK homes had their cavity walls filled with insulation over the last two decades, much of it free or subsidised under government energy schemes such as CERT, CESP, the Green Deal and the Energy Company Obligation (ECO). For most properties it works well. But where insulation was fitted into a wall that was never suitable – for example a home in a severe wind-driven rain area, a wall with poor pointing or rubble in the cavity, or a property already prone to penetrating damp – the result can be the opposite of what was promised: damp internal walls, black mould, peeling plaster, musty smells, cold spots and rising heating bills. This calculator gives a realistic, evidence-based estimate of what a claim for failed cavity wall insulation might be worth, broken down into the cost of removing the insulation, putting right the damage, and damages for the disruption you have suffered. It is general information for planning only, not legal advice, and the figures are estimates rather than a promise of any settlement.
Why does cavity wall insulation fail?
Cavity wall insulation is designed to sit in the air gap between the two skins (leaves) of an external wall. That air gap exists for a reason: in driving rain, the outer leaf gets wet, and the cavity lets that moisture drain away and evaporate rather than crossing to the inner wall. When the cavity is filled with the wrong material, in the wrong property, that protective gap is bridged and water can track across to the inside.
The British Standard for this work, BS 8208, requires installers to assess a wall's suitability before filling it – including the property's exposure to wind-driven rain using the Building Research Establishment (BRE) exposure zones. Homes in the most exposed Zone 3 and Zone 4 areas – common along the west coast, in Wales, the South West, the North West and parts of Scotland – are frequently not suitable for standard cavity fill. Many failed installations happened because that survey was rushed, done remotely, or ignored entirely so that an installer could hit scheme targets. Other common causes include debris or mortar snots bridging the cavity, gaps and slumping in the fill, and incompatible insulants in already-damp walls.
What can you claim for?
A cavity wall insulation claim is usually made against the original installer for negligent assessment or workmanship, or under a guarantee such as the Cavity Insulation Guarantee Agency (CIGA) 25-year guarantee where one exists. A well-evidenced claim typically combines several heads of loss:
- Extraction (removal) costs – specialist contractors remove the failed insulation, usually by drilling and vacuuming it out. For a standard house this commonly runs from around £1,500 to £4,500 depending on size and access.
- Repair and remediation – treating and drying the damp, replacing damaged plaster and timber, mould treatment and redecoration. This is often the largest part of a claim.
- Damaged belongings (special damages) – carpets, furniture, clothing and electricals ruined by damp and mould, supported by receipts or photos.
- General damages – a sum for the distress, inconvenience and loss of enjoyment of your home, which tends to be larger the longer and more severe the problem.
- Wasted energy savings – in some cases, the higher heating costs caused by wet, ineffective insulation.
How the calculator works
The tool builds an estimate from four inputs:
- Property type sets a typical extraction cost, because a detached house has far more external wall to clear than a flat or mid-terrace.
- Severity of damage drives the repair and remediation figure and the baseline for general damages – minor, moderate or severe.
- Years affected scales the general damages upward (capped at six years), reflecting how courts and insurers treat long-running disruption more seriously.
- Damaged belongings are added on top as special damages, and an exposure-zone flag notes when the underlying installation may have been negligent.
The result shows a central total, a realistic range (roughly 70% to 135% of the central figure) and an illustrative amount left after a typical 25% no-win no-fee success fee. These are deliberately conservative planning estimates – your actual entitlement depends on a survey and the evidence in your individual case.
Worked example
Take a semi-detached house in a coastal town where cavity wall insulation was fitted eight years ago under an energy grant. The owners, the Hughes family, noticed black mould in two bedrooms and a damp, cold north-facing wall about four years ago; a surveyor has since confirmed the wet cavity fill is the cause. Using the calculator with property type "semi-detached", severity "moderate", four years affected and £700 of ruined belongings:
- Extraction / removal: about £3,000
- Damp repair, replastering and redecoration: about £3,000
- General damages (moderate, four years): about £2,720
- Damaged belongings: £700
That gives a central estimate of roughly £9,420, with a realistic range of about £6,600 to £12,700. On a no-win no-fee basis with a 25% success fee, the family might keep in the region of £7,000 – though survey fees and other disbursements could change that. Because the property is in an exposed area where the cavity may never have been suitable, an independent borescope survey would be the most important next step to support the negligence claim.
Who can make a claim?
You may have a claim if you own the property and the insulation has caused damp, mould or related damage that a survey links to the cavity fill. Homeowners usually claim against the installer (often via no-win no-fee solicitors) or through a CIGA guarantee. If you bought the home after the insulation was fitted, you may still be able to claim – guarantees can be transferable and negligence claims are not always blocked by a change of owner, so take advice. Tenants in rented homes generally pursue the landlord instead, using housing disrepair rules or the Homes (Fitness for Human Habitation) Act 2018, and social housing tenants are additionally protected by the new damp-and-mould timescales introduced after the Awaab Ishak case.
Typical compensation bands
The table below shows broad, illustrative ranges drawn from how these claims are commonly settled. They are estimates, not a tariff – every case turns on its own survey evidence.
| Scenario | Damage level | Typical total estimate |
|---|---|---|
| Flat or mid-terrace, localised damp | Minor | £2,000 – £5,000 |
| Terraced / semi, damp in several rooms | Moderate | £5,000 – £10,000 |
| Semi / detached, widespread damage | Severe | £10,000 – £15,000+ |
| Detached with structural/timber damage | Very severe | £15,000+ |
Common mistakes to avoid
- Removing the insulation before it is surveyed. Your evidence lives in the cavity – get an independent borescope survey and photographs first.
- Letting the installer "fix" it for free without advice. A patch repair can reset guarantees and weaken a later claim; understand your options first.
- Missing the time limit. Acting late can bar an otherwise strong claim under the Limitation Act 1980.
- Signing a no-win no-fee agreement without reading it. Check the success-fee percentage and what you pay for disbursements if you lose.
- Treating mould as just a lifestyle issue. Persistent damp with no obvious cause often points to a building defect, not condensation from drying washing.
Frequently asked questions
Can I claim for failed cavity wall insulation?
You may be able to claim if cavity wall insulation was installed in an unsuitable property – for example one in a severe wind-driven rain exposure zone – and it has caused damp, condensation, mould or cold spots. Claims are usually made against the original installer for negligent assessment or installation, or through a CIGA guarantee where one exists. Every case is different, so seek advice from a regulated solicitor.
How much compensation can I get?
There is no fixed figure. A claim usually combines the cost of extracting the insulation (often around £1,500 to £4,500 depending on property size), the cost of repairing damp, replastering and redecoration, the value of any damaged belongings, and general damages for distress and inconvenience. Totals commonly fall in the low thousands up to around £15,000, but the amount depends entirely on the evidence in your case.
What is the CIGA guarantee?
The Cavity Insulation Guarantee Agency (CIGA) provides an independent 25-year guarantee on cavity wall insulation fitted by its registered installers. If your insulation has failed and you hold a CIGA guarantee, you can ask CIGA to investigate and arrange remedial work. You can still pursue a separate legal claim against the installer for losses a guarantee does not cover.
Is there a time limit to claim?
Generally you have six years from the negligence or breach of contract under the Limitation Act 1980. Where damage was hidden, a separate rule can allow three years from when you first knew, or reasonably should have known, about the problem, subject to a long-stop. Because limitation can be complex, get legal advice as soon as you suspect a problem.
Does no-win no-fee cover these claims?
Many solicitors handle cavity wall insulation claims on a no-win no-fee (conditional fee) basis, so you pay nothing if the claim fails. If you win, a success fee is deducted from your compensation – often up to around 25% – so read the agreement carefully and check what you would pay for disbursements such as surveyor reports.
Can damp and mould really affect my health?
Yes. The NHS warns that damp and mould can cause or worsen respiratory problems, allergies and asthma, and can particularly affect babies, older people and those with existing breathing conditions. Any health impact should be documented by your GP and can form part of a claim.
Sources: suitability assessment and exposure zones reflect BRE guidance and BS 8208; guarantee details from the Cavity Insulation Guarantee Agency (CIGA); tenant rights from GOV.UK – Private renting repairs and the Homes (Fitness for Human Habitation) Act 2018; time limits from the Limitation Act 1980; health effects from the NHS. Figures are estimates for general guidance only and not legal advice.