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.
Browse all findings
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- Damp proof course issues
- Underpinning
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- Roof issues
- Timber decay
- Electrical issues
- Non-standard construction
- Asbestos containing materials
- Roof covering needs repair
- Single skin wall construction
- Timber decay / wet rot
- Settlement cracks
- RAAC concrete
- Wall tie failure
- Party wall matters
- Drainage issues
- Subsidence monitoring
- Full electrical rewire needed
- Flat roof condition
- Cladding issues
- EWS1 form required
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- Structural crack BRE category 3
- Structural crack BRE category 4-5
- Chimney stack movement
- Chimney flashing failure
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- Bay window cracking
- Flat roof ponding
- Cold roof inadequate ventilation
- Warm roof insulation issues
- Prefab concrete construction
- Large panel system (LPS) construction
- Rising damp
- Penetrating damp
- Condensation vs damp distinction
- Dry rot (Serpula lacrymans)
- Woodworm
- Timber floor springiness
- Cellar / basement damp
- Outdated electrics (60-amp fuse board)
- Aluminium wiring
- Partial rewire needed
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- Back boiler
- Unvented hot water cylinder issues
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- Lead paint
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- Asbestos floor tiles
- Asbestos cement roof
- Asbestos insulated board (AIB)
- Asbestos soffit boards
- Pointing / repointing needed
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- Pebbledash delamination
- UPVC window seal failure
- Sash window condition
- Flat roof membrane condition
- Zinc roof
- Felt roof condition
- Corrugated asbestos roof
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- External wall insulation issues
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- No planning permission for extension
- Certificate of lawfulness needed
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- PRC (precast reinforced concrete) house
- Airey house
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- Loft conversion: no building regs
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- Shared or private sewer
- Blocked or collapsed drains
- Cesspit or septic tank
- Solid fuel heating
- No mains gas supply
- Low water pressure
- Private water supply
- Wimpey No-Fines concrete house
- Reema construction
- Unity or Boot construction
- Laing Easiform
- Cornish Unit house
- Cross-wall construction
- In-situ concrete construction
- Oak frame construction
- Radon: mitigation required
- Missing or inadequate fire alarms
- Single staircase: means of escape
- No earthing or bonding
Tool shortcut
Check the property before you offer
Flood, subsidence, EPC, crime, schools, transport, broadband, tenure, age, listed status and price checks where data is available.
Run a free previewCross-check this finding with EPC, building age, and address-specific risk data.
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
Run the check on this address
The Survey Decoder explains the wording. The full report adds address-specific flood, subsidence, EPC, crime, listed status, building age and price comparison data, so a single finding isn't judged in isolation.
Run the check
Check the property before you offer
Flood, subsidence, EPC, crime, schools, transport, broadband, tenure, age, listed status and price checks where data is available.
Run a free previewRead next
UPVC window seal failure , often sits near double glazing condensation (failed units) on a survey and is the next thing to check.
Editorial review
Editorial owner: BiteRight Ltd, operator of MyPropertyScan. We review buyer guides against UK public property datasets, RICS survey wording, lender requirements, and common buyer questions.
Pages are updated when source coverage, property-risk guidance, survey cost assumptions, or product checks materially change. Methodology and dataset limitations are explained on the MyPropertyScan methodology page.
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.