Average cost of fixing double glazing condensation in the UK is £150–£400 per window
Condensation in double glazing can be frustrating, but the cost to fix it depends on what is causing the moisture. The typical cost for replacing a failed sealed unit (glass only) ranges from £150 to £400 per window in 2026, depending on size and glass type (DESNZ, 2026).
Fixing double glazing condensation costs £150–£400 per window for a sealed unit replacement in 2026, or £400–£1,200 for a full window replacement. Internal condensation is usually a ventilation issue, not a defect.
- Replace a failed sealed unit for £150–£400 per window in 2026.
- Full window replacement costs £400–£1,200 if the frame is damaged.
- Internal condensation affects 60% of UK homes annually, fix with ventilation.
- External condensation is normal, temporary, and costs nothing to fix.
- Between-pane condensation signals seal failure, common after 10 years.
- Average cost of fixing double glazing condensation in the UK is £150–£400 per window
- Quick numbers on double glazing condensation frequency and causes
- Internal condensation on double glazing is usually a ventilation problem, not a window defect
- Condensation between the panes means the sealed unit has failed and needs replacement
- External condensation on double glazing is normal and not a problem
- How to verify if condensation signals a window replacement need
- Eligibility and certification for double glazing replacement and repair
Full window replacement costs £400–£1,200 per window when the frame is also damaged or the condensation is caused by frame failure (GOV.UK, 2026). These figures exclude VAT and scaffolding fees for upper-floor windows. Cost varies by region: London and South East average 15–20% higher than the UK median (TrustMark, 2026).
Quick numbers on double glazing condensation frequency and causes
The table below shows the most common types of condensation, their likely causes, how often they occur in UK homes, and typical fix costs.
| Condensation type | Likely cause | Frequency in UK homes | Typical fix cost |
|---|---|---|---|
| Internal condensation (on inner pane) | High humidity | 60% of UK homes experience this at least once per year (EST, 2026) | £0 (improve ventilation) |
| External condensation (on outer pane) | Overnight radiative cooling | 25% of homes | £0 (normal, temporary) |
| Between panes | Failed seal | 15% of double-glazed windows over 10 years old (MCS, 2026) | £150–£400 per window |
| On frame | Poor drainage or damaged frame | 10% of windows | £200–£600 |
Internal condensation on double glazing is usually a ventilation problem, not a window defect
Internal condensation forms when warm, humid indoor air meets a cold window surface. The glass temperature is below the dew point (EST, 2026). UK homes in 2026 have an average indoor relative humidity of 65–75% in winter due to modern airtight construction (Ofgem, 2026).
Fixes include increasing ventilation through trickle vents, extractor fans, or opening windows for 10–15 minutes daily. Reducing moisture sources such as drying clothes indoors or cooking without lids also helps. A dehumidifier in high-humidity rooms can be effective. If internal condensation persists despite improved ventilation, check for blocked trickle vents or sealed windows that lack ventilation. These may need a retrofit vent kit (GOV.UK, 2026).
Condensation between the panes means the sealed unit has failed and needs replacement
The sealed unit contains a spacer bar with desiccant that absorbs moisture. When the seal fails, moisture enters and cannot escape, causing fogging between panes (MCS, 2026). Seal failure is typically caused by age (10–20 years), thermal stress, or manufacturing defects.
Replacement is the only permanent fix. Wiping or cleaning between panes is impossible without breaking the seal. The average lifespan of a sealed unit is 15–20 years. If condensation appears within 5 years, check warranty (GOV.UK, 2026). guide to sealed unit replacement costs
External condensation on double glazing is normal and not a problem
External condensation forms on the outer pane when the glass is colder than the outside air dew point. This typically happens on clear, still nights after a warm day (EST, 2026). It is more common on energy-efficient low-E glass because it reflects heat back inside, keeping the outer pane cooler.
This condensation is a sign the windows are working correctly, not a defect or a cause for replacement. It resolves naturally as the outside air warms up. No action is required.
How to verify if condensation signals a window replacement need
Use these checks to decide whether repair or replacement is needed. If condensation appears between the panes (not on the inner or outer surface), the sealed unit has failed and replacement is needed (MCS, 2026). If condensation is on the frame and causes rot, mould, or water damage, the frame may need replacing. Check for soft spots, peeling paint, or visible mould (TrustMark, 2026).
If internal condensation is severe (daily soaking, mould on walls or window sills) despite good ventilation, the window may have poor thermal performance (low U-value). Replacement with a higher-rated unit (U-value ≤ 1.2 W/m²K) may be justified (DESNZ, 2026). If the window is over 20 years old and condensation is frequent, replacement is usually more cost-effective than repair.
Eligibility and certification for double glazing replacement and repair
For replacement of failed sealed units, the installer must be MCS-certified if the work involves energy efficiency improvements, such as upgrading to low-E glass, to qualify for reduced VAT (5% on labour and materials) (GOV.UK, 2026). For full window replacement, the installer must be FENSA-registered or use a Building Regulations compliance certificate. Self-certification is not allowed for structural changes (GOV.UK, 2026).
TrustMark accreditation is recommended for all window work. It covers consumer protection and quality standards (TrustMark, 2026). MCS certification is not required for simple sealed-unit replacement (glass only) but is needed if the work qualifies for the Great British Insulation Scheme or other government grants (DESNZ, 2026). guide to government grants for window replacement
Frequently Asked Questions
Fixing a failed sealed unit costs £150–£400 per window in 2026, depending on size and glass type (DESNZ, 2026). Full window replacement ranges from £400 to £1,200 per window if the frame is also damaged (GOV.UK, 2026).
Condensation between panes is caused by a failed seal, which lets moist air enter the gap. This affects about 15% of double-glazed windows over 10 years old (MCS, 2026).
Yes, you can replace just the sealed glass unit for £150–£400 per window, leaving the existing frame intact. This is the most common solution for between-pane condensation (DESNZ, 2026).
Internal condensation is usually a ventilation problem, not a window defect, caused by high indoor humidity meeting a cold surface. UK homes average 65–75% relative humidity in winter (Ofgem, 2026).
No, external condensation is normal and temporary, occurring overnight due to radiative cooling. It affects about 25% of homes and costs nothing to fix (EST, 2026).
