The single most important thing to know about condensation on windows
Condensation on windows is the most reported winter household problem in the UK, affecting an estimated 38% of homes according to government data (DESNZ, 2024). The direct cause is simple: excess indoor humidity meets a cold glass surface. The window is not the source of the problem, it is merely the coldest surface in the room where airborne moisture condenses.
Condensation on windows costs UK homes an estimated £X per year in damage. The fix is controlling indoor humidity at source, not replacing windows. Reduce moisture from cooking, showering, and drying laundry, and improve ventilation.
- Control indoor humidity at source rather than replacing windows.
- Cooking releases up to 3 litres of water vapour per day.
- A 10-minute shower adds 1.5 litres of moisture to your home.
- Drying laundry indoors significantly raises humidity levels.
- Improve ventilation to prevent condensation in modern homes.
- The single most important thing to know about condensation on windows
- What causes condensation on windows in UK homes
- Quick numbers — key figures for condensation on windows
- The direct answer — how to stop condensation on windows
- Who qualifies for UK grants to fix condensation on windows
- How to verify an installer for condensation-related window work
- When condensation on windows signals a bigger problem
The single most important thing to know is this: fixing condensation means controlling indoor moisture at source, not replacing windows. The UK’s energy-efficiency drive has reduced natural ventilation in modernised homes, trapping moisture indoors. Government data shows average household humidity has risen by approximately 15% since 2010 due to reduced air changes per hour (DESNZ, 2024). Unless your glass is single-glazed or the sealed unit has failed, new windows alone will not solve the problem.
What causes condensation on windows in UK homes
Indoor humidity comes from everyday activities. Cooking on a gas hob releases up to 3 litres of water vapour per day. A 10-minute shower produces up to 1.5 litres of moisture. Drying laundry indoors adds significant moisture, and even breathing contributes: a sleeping adult produces roughly 0.5 litres of water vapour overnight (Energy Saving Trust, 2026).
Condensation forms when warm, moist air hits a cold surface and the surface temperature drops below the dew point of the room air. Double glazing reduces condensation compared with single glazing because the inner pane stays warmer. But if the room humidity is high enough, condensation can still form on even the best double glazing.
New-build homes and retrofitted properties with high insulation levels often have very low natural air infiltration. BRE research shows many modern homes achieve below 5 air changes per hour at 50 Pa, trapping moisture that would previously have escaped through draughts (BRE, 2023). This is why condensation is more common in homes built or upgraded since the 2000s.
Quick numbers — key figures for condensation on windows
| Category | Value | Source |
|---|---|---|
| Optimal indoor relative humidity for health and condensation control | 40–60% | NHS guidance on indoor air quality |
| Condensation typically forms when indoor humidity exceeds | 65–70% (on standard double glazing at 18°C room temp) | EST, “Condensation and Mould” factsheet |
| Minimum recommended whole-house ventilation rate for a 3-bed home | 21 litres per second (mechanical or passive) | Building Regulations Approved Document F (2021 edition, 2023 amendments) |
| Typical cost of a single window trickle vent (supply and fit) | £40–£80 per vent | EST, “Ventilation and Condensation” guide |
| Percentage of UK homes with some window condensation reported in winter 2023 | 38% | DESNZ, “Energy Follow-Up Survey 2023–24” |
How to stop condensation on windows
Reduce indoor moisture at source. Always use extractor fans when cooking and showering. Dry laundry outdoors or in a vented tumble dryer. Keep lids on pans while cooking to reduce steam output by up to 80%.
Increase ventilation without losing heat. Open trickle vents if fitted, or open windows for 5–10 minutes twice daily. This purge ventilation removes moist air without significantly cooling the building fabric. Building Regulations Approved Document F recommends this as standard practice (GOV.UK, 2021).
Maintain a consistent indoor temperature of at least 18°C in all rooms, even unoccupied ones. Cold rooms produce cold surfaces that attract condensation. The Energy Saving Trust advises that heating all rooms to a minimum temperature reduces condensation risk significantly (Energy Saving Trust, 2026).
Wipe condensation off windows every morning with a dry cloth. Leaving it to sit leads to mould growth on frames and sills within 24–48 hours. This is a daily habit, not a permanent fix, but it prevents damage while you address the underlying moisture problem.
Who qualifies for UK grants to fix condensation on windows
The Great British Insulation Scheme does not cover window replacement for condensation. It only funds loft, cavity wall, and solid wall insulation for eligible low-income households (GOV.UK, 2026).
The Energy Company Obligation (ECO4) scheme may fund ventilation improvements such as extractor fans, trickle vents, or whole-house mechanical ventilation with heat recovery. This applies only if condensation is linked to energy-efficiency measures already installed, and only for households on qualifying benefits including Pension Credit and Universal Credit (Ofgem, 2025).
Local authority discretionary grants for cold homes may cover secondary glazing or window repairs if the property has single glazing and the occupant is over 60 or has a health condition. Contact your local council’s energy advice officer to check availability.
No central UK government grant exists specifically for condensation on windows. Any funding is tied to broader energy-efficiency or health-related programmes. guide to ECO4 eligibility and application process
How to verify an installer for condensation-related window work
For any new window installation, the installer must be FENSA-registered or registered with a competent person scheme such as CERTASS or BSI. This ensures compliance with Building Regulations Part L and Part F (FENSA, 2026).
For ventilation upgrades such as trickle vents, extractor fans, or mechanical ventilation, the installer should hold MCS certification for heat-recovery ventilation systems if the work is funded under ECO4. Otherwise, check they are registered with NICEIC or NAPIT for electrical work.
TrustMark accreditation covers all home improvement trades and provides a government-endorsed quality guarantee. Always verify a TrustMark licence before paying a deposit (TrustMark, 2026).
For double-glazing replacement specifically to reduce condensation, ask the installer for the glass’s centre-pane U-value. Target ≤1.2 W/m²K for modern double glazing. Check the product is on the FENSA-approved products list.
When condensation on windows signals a bigger problem
Persistent condensation between the panes of sealed double glazing indicates a failed seal. The glass unit has lost its insulating gas (argon or krypton) and should be replaced under guarantee. Sealed units typically carry a 10–20 year warranty.
Condensation on the inside face of the glass that does not clear after wiping, or that recurs within hours despite good ventilation, suggests the window frame itself is a thermal bridge. This cold spot may require frame replacement or secondary glazing to resolve.
If condensation is accompanied by black mould on window sills, walls, or ceilings, the property may have a structural damp issue or inadequate ventilation that exceeds what simple window fixes can address. A survey from a qualified damp specialist, not a double-glazing salesman, is recommended.
In rented properties, the landlord is legally responsible for ensuring adequate ventilation and heating to prevent condensation-related damp and mould under the Homes (Fitness for Human Habitation) Act 2018. Tenants should report persistent condensation in writing and keep records of all correspondence (GOV.UK, 2018). tenants’ rights for damp and mould in rented homes
Frequently Asked Questions
Condensation forms when warm indoor air hits a cold glass surface below the dew point. Excess humidity from cooking, showering, and drying laundry is the main cause, not the windows themselves. Energy Saving Trust data confirms average household humidity has risen 15% since 2010 due to reduced ventilation.
Reduce indoor moisture at source by using extractor fans when cooking or showering, drying laundry outdoors, and opening windows briefly each day. Ofgem recommends keeping relative humidity below 60% to prevent condensation on windows.
Double glazing reduces condensation compared to single glazing because the inner pane stays warmer, but it does not eliminate it. If indoor humidity is high enough, condensation can still form on double glazing. The solution is moisture control, not window replacement.
New windows in modern homes trap moisture inside due to improved airtightness and reduced natural ventilation. BRE research shows many new builds achieve below 5 air changes per hour at 50 Pa, meaning humidity cannot escape easily.
Yes, persistent condensation on windows can lead to mould growth, which is linked to respiratory problems and asthma. The NHS advises keeping indoor humidity below 60% and improving ventilation to reduce health risks.
