Survey finding
Failed double glazing units: what to do
Misted-up double glazing is on most UK surveys for properties over 15 years old. This page covers what causes it, what replacement costs, and when to upgrade frames vs units.
Last updated: 6 May 2026. Editorially reviewed: 20 May 2026.
Finding
Double glazing condensation (failed units)
What this usually means
Condensation between the panes of a double-glazed window indicates seal failure of the sealed unit. Once the seal fails, the inert gas escapes and moisture condenses inside, the unit no longer insulates effectively. UK double glazing typically lasts 15–25 years before a meaningful share of units fail.
Why it matters
Failed sealed units are cosmetic and thermal-performance issues, not safety. Replace as a planned cost. Lenders never refuse on this.
Ask your surveyor
- Check:How many units show seal failure?
- Check:Are the frames serviceable for re-glazing or do they also need replacing?
Ask the seller
- Check:When were the windows installed?
- Check:Have any units been replaced before, and are records kept?
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
Cosmetic. Note for budget but not a negotiation lever in itself.
Typical cost to fix
Replace a single failed sealed unit (most uPVC frames): £80–£200 per unit. Replace whole windows with new double-glazed units: £400–£900 per window. Sash conversion from single to double glazed: £500–£1,200 per window.
Mortgage impact
Not a mortgage issue.
Insurance impact
Not an insurance issue.
When to pull out
Never a pull-out trigger.
When to renegotiate, and by how much
Get a glazier's quote per failed unit. Negotiate on full quote.
Thinking of pulling out or renegotiating? What to do after a bad survey
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Flood, subsidence, EPC, crime, schools, transport, broadband, tenure, age, listed status and price checks where data is available.
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UPVC window seal failure , often sits near double glazing condensation (failed units) on a survey and is the next thing to check.
How 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.