Survey finding
Cavity wall insulation problems on your survey
Failed CWI is a common Cat 3 finding. This page covers the diagnosis and remediation.
Last updated: 6 May 2026. Editorially reviewed: 20 May 2026.
Finding
Cavity wall insulation issues
What this usually means
Cavity wall insulation, when poorly installed or applied to inappropriate properties (exposed sites, narrow cavities), can bridge moisture across the cavity, causing internal damp on inner leaf walls. CIGA-registered installers offer a 25-year guarantee.
Why it matters
Damp from CWI failure is widespread and often misdiagnosed as rising damp.
Ask your surveyor
- Check:Is there evidence of cavity bridging or saturation?
- Check:Is CIGA documentation available?
Ask the seller
- Check:When was CWI installed and by whom?
- Check:Is the CIGA guarantee documentation transferable?
Next steps
- •Get two written quotes from local trades before negotiating with the seller.
- •Speak to your mortgage broker before exchanging if the finding affects mortgageability.
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What you need to know
Severity
Significant. Specialist follow-up usually warranted before exchange.
Typical cost to fix
Borescope inspection £200-£500. CWI extraction £1,500-£3,500. Re-insulation with appropriate material £1,000-£2,500. Internal replastering after drying £40-£60/m².
Mortgage impact
Standard unless severe damp confirmed.
Insurance impact
CIGA guarantees cover proper installations; gradual damage outside scope.
When to pull out
Not on its own.
When to renegotiate, and by how much
Extraction plus re-insulation plus internal making good; typical £3,000-£7,000.
Thinking of pulling out or renegotiating? What to do after a bad survey
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Run a free previewHow MyPropertyScan produces this guide, and what it is not
Published by MyPropertyScan and written by Ziad Nasr, who is accountable for its accuracy. No page here is written or reviewed by a chartered surveyor, conveyancer or regulated adviser, and we do not claim otherwise.
This page is not:
- Chartered surveying — we do not inspect properties or produce RICS Home Survey reports
- Legal advice — we do not act as conveyancers or advise on title, tenure or contracts
- Mortgage or insurance advice — we are not regulated by the FCA and give no recommendations
Figures and process steps come from the published UK datasets and standards listed on this page, not from professional practice. Pages are updated when source coverage, survey cost assumptions, or lender and legal requirements materially change. Dataset limitations are set out on the methodology page.
Spotted something out of date or wrong? Email hello@mypropertyscan.com and we will correct it and change the update date.
Sources used
We use UK public and specialist sources where they are available. Public datasets can be incomplete, delayed, or missing for some addresses. Treat them as a starting point, not as a replacement for professional advice.
Source standard: preference goes to official government datasets, statutory bodies, professional standards, and primary dataset publishers. We cite the source family on the page and explain coverage limits rather than filling gaps with unsupported estimates.
- Professional standard: RICS Home Survey StandardRICS standard for condition-based residential surveys in the UK.
- Learn more from: RICS consumer guide to surveysConsumer-facing guide to survey types and when each level is appropriate.
- Official guidance: GOV.UK buying or selling your homeGovernment overview of the home buying and selling process.