TL;DR
- Diagnose first by location: condensation on the inside means a humidity or ventilation issue; on the outside means efficient glazing; between the panes means a failed sealed unit; around the frame points to thermal bridging or installation issues.
- The fix rests on four pillars: reduce moisture at source, improve ventilation, keep room temperatures stable, and address cold surfaces. Most UK homes resolve condensation within the free-to-mid-cost range.
- Aim for 40 to 60 per cent relative humidity. Open trickle vents in winter rather than closing them, run extractor fans correctly, and air rooms briefly each morning.
- New windows alone rarely solve persistent condensation. Modern compliant glazing keeps surfaces warmer, but moisture management and ventilation must be addressed alongside any glazing upgrade.
Condensation on windows is one of those household problems that feels minor in isolation and significant when you stop to think about it. A few drops on the bedroom glass on a cold morning seem harmless enough; left unaddressed across a winter, the same condensation feeds black mould around the reveal, swells the timber on a sash, lifts the paint at the corners and quietly damages soft furnishings nearby. The underlying cause is rarely faulty windows. It is usually a combination of humidity, ventilation and surface temperature, and the right fix depends on which of those factors is actually driving the problem in your home.
This guide walks through how to diagnose the cause of condensation on your windows, what each pattern actually means, and the genuinely useful steps that resolve the issue without wasting heat or chasing the wrong solution. By the end, you will know whether you have a ventilation problem, a glazing problem or a humidity problem, and which fix will actually move the needle in your home.
Quick answer: How to stop condensation on windows
For most UK homes, condensation on the inside of windows is resolved by a combination of four things: reducing moisture at source (cooking lids, shorter showers, drying clothes outside or in a vented dryer), improving background ventilation (using extractor fans properly, opening trickle vents, briefly airing rooms each morning), keeping room temperatures stable rather than letting them swing, and addressing any specific cold spots where condensation concentrates.
If condensation is forming inside the sealed glazing unit (where you cannot wipe it away), the unit has failed and needs replacement. If condensation is forming on the outside of the glass on cold mornings, the glazing is performing well and no fix is needed. If condensation is forming on the room-facing surface of the glass or around the frame and reveals, the issue is humidity and ventilation rather than the windows themselves.
The honest framing is that new windows alone rarely solve persistent condensation. Modern compliant windows reduce the cold-glass effect that causes surface condensation, but they do not change the moisture in the room. Both pieces matter, and addressing only one of them is the most common reason homeowners spend money without solving the problem.
Why does condensation happen in UK homes
Condensation forms when warm, moist air contacts a surface cool enough to drop the air below its dew point. The water vapour the air was holding turns back into liquid water on the cold surface. Windows are the most common location because the glass is usually the coldest internal surface in the room, particularly on still cold nights.
UK homes are well-suited to producing condensation. Average outdoor temperatures from October to April are low enough to keep window glass cold for long periods. UK lifestyles add significant moisture to the indoor air: cooking, showering, drying clothes indoors, breathing while sleeping, and the steady evaporation of moisture from indoor plants and aquariums. A typical four-person household generates around 12 to 20 litres of moisture per day, all of which the air has to absorb or expel through ventilation.
The problem is more acute in winter, when homeowners reasonably keep windows closed for warmth, and again most acute in bedrooms and bathrooms where moisture concentrates. New-build homes can be particularly affected during their first one to two years, because construction processes (plaster, screed, paint, mortar) introduce significant moisture that takes months to fully dry.
The cure is not to eliminate moisture; that is impossible and undesirable. The cure is to manage moisture levels and surface temperatures together so the dew point is rarely reached on the windows. This is what good UK home performance looks like in practice.
First: identify where the condensation is
The single most important diagnostic step is identifying exactly where the condensation is forming. Different locations have different causes and different fixes.
Condensation on the inside (room-facing) surface of the glass
This is the most common pattern. Warm, moist air from the room contacts the cooler glass surface and condenses. The fix is a combination of reducing room humidity, improving ventilation, and keeping the glass surface warmer (which modern compliant windows do automatically). It is rarely a sign that the windows are faulty; it is a sign that the air is too humid for the room and surface temperatures.
Condensation on the outside surface of the glass
This appears on cold, still mornings, particularly in autumn when nights cool quickly and dew forms readily. External condensation is actually a sign of efficient glazing: the outer pane stays cooler than the surrounding air because the inside of the unit is well insulated, allowing dew to form briefly before the morning warms. It clears within an hour or two and requires no action. If your new windows show external condensation, the installer has done their job.
Condensation between the panes (inside the sealed unit)
This is the only pattern that indicates a window fault. Condensation inside the sealed unit means the seals around the unit have failed and the inert gas (usually argon) has escaped. The unit no longer performs thermally as designed. The condensation cannot be wiped away because it sits inside the cassette. On a single failed unit in a sound frame, the sealed unit alone can be replaced for £150 to £400. On multiple failed units in tired frames, full window replacement is usually the better answer.
Condensation around the frame and the surrounding wall
This indicates that the surfaces beyond the glass are also dropping below the dew point. The frame, the reveal plaster, and sometimes the wall around the window are all cool enough to attract moisture. The cause is usually thermal bridging at the frame-to-wall junction, poor insulation in the surrounding wall, or a combination with high room humidity. The fix involves both the moisture management above and addressing any specific thermal weaknesses around the opening.
The four-part fix for window condensation
Effective condensation control rests on four pillars. Most homes need attention to all four, with the relative weight depending on the property and the lifestyle.
Reduce moisture at the source
The single biggest lever for most UK homes is reducing how much moisture is generated in the first place. Cover pots when cooking. Use lids on saucepans wherever possible. Run extractor fans in the kitchen during cooking and for 15 minutes afterwards. Take shorter showers; run the bathroom extractor for the full duration and 20 minutes afterwards. Dry clothes outside whenever possible, or in a vented or condenser tumble dryer rather than indoors. Avoid drying clothes on radiators, which puts the moisture directly into the room.
If you have to dry clothes indoors, do it in a single closed room with the window cracked or trickle vents open and the door closed. Better still, run a dehumidifier in the same room while the clothes dry; this captures the moisture rather than letting it migrate through the home.
A small hygrometer (£10 to £25 on the high street or online) tells you what the actual humidity level in your home is. Aim for 40 to 60 per cent relative humidity through the heating season. Above 60 per cent, the condensation and mould risk rises sharply. Below 40 per cent, the air can feel too dry. The hygrometer is the single most useful diagnostic tool a homeowner can buy.
Improve ventilation
Ventilation is the second pillar, and it is the one most homeowners get wrong by trying to seal everything tight to save heat. Some background ventilation is essential to remove moisture-laden air from the home; without it, even modest moisture generation builds up to problematic levels.
Open trickle vents in winter rather than closing them. They are sized to provide background ventilation without significant heat loss, and the energy cost is far smaller than the cost of running the heating harder to clear condensation later. Modern compliant replacement windows are now required by Approved Document F to include trickle vents on most installations, even where the originals did not have them.
Use extractor fans correctly. Run the kitchen extractor during cooking and for 15 minutes afterwards. Run the bathroom extractor during showers and for 20 minutes afterwards. Open the bathroom window when leaving the room rather than closing it. Brief, energetic ventilation is more effective than continuous low-level ventilation.
Air rooms briefly each morning. Opening windows wide for five to ten minutes after waking up clears the moisture-laden air from sleeping (a typical adult exhales 250 to 500ml of water vapour overnight) and replaces it with drier outside air. The room cools briefly but recovers within an hour, and the heating system never has to work against high humidity.
For homes with persistent issues despite these measures, mechanical ventilation upgrades are worth considering. Positive Input Ventilation (PIV) systems push fresh, filtered air into the home from a roof-mounted unit, displacing moisture-laden air through trickle vents. Mechanical Ventilation with Heat Recovery (MVHR) systems extract moist air and recover heat from it for use in incoming fresh air. Both are significant investments (£1,500 to £6,000 fitted depending on system and property) and best suited to homes where the underlying construction is airtight.
Keep temperatures stable
Sudden temperature swings cause condensation. A cold bedroom warmed quickly in the morning catches moisture on every cold surface as the air heats up; a kitchen heated only when in use stores moisture overnight in the cooler walls.
The right approach is consistent background heating across the home, particularly in the heating season. A whole-house thermostat set at 18 to 20°C, with rooms maintained at similar temperatures, performs better than individually heating one or two rooms while leaving others cold. The cumulative gas or electricity cost is often surprisingly similar, and condensation reduces dramatically.
For homes with rooms that habitually run cold (north-facing bedrooms, ground-floor extensions, conservatories), targeted improvements often help more than running the whole heating system harder. Better insulation in the affected room, draught-proofing of doors, and quality double or triple glazing on the relevant windows all reduce the cold-surface effect that drives condensation.
Improve glazing and insulation
The glass surface temperature is the final lever. Modern compliant double glazing keeps the inside surface of the glass several degrees warmer in winter than older single or early double glazing. This raises the surface above the dew point in most rooms and most conditions, eliminating condensation on the glass even where humidity remains moderate.
For homes with persistent condensation despite good ventilation and moisture management, the surface temperature of the glass is often the limiting factor. Replacing tired older windows (single glazing, early 1990s double glazing with failed seals) with quality modern double glazing typically resolves the issue when combined with the other measures.
Triple glazing reaches lower U-values still, with whole-window U-values of 0.8 to 1.0 W/m²K achievable on premium specifications. The improvement over quality double glazing is real but smaller than the headline figures suggest. For homes with severe condensation in specific rooms (north-facing bedrooms, exposed elevations), triple glazing on those rooms only is a targeted upgrade that often delivers good value.
Secondary glazing (a separate internal pane fitted inside the existing window) is the right answer for listed buildings, conservation areas with restrictive Article 4 Directions, and properties where the original windows must be preserved. Whole-system U-values of around 1.5 W/m²K are achievable when paired with sound primary windows, at £300 to £600 per window fitted.
Room-by-room advice
Different rooms generate moisture in different ways and benefit from different fixes.
Bedrooms
Bedroom condensation is usually worst in the morning, after a night of breathing has added significant moisture to the room. Open the window or trickle vents wide for five to ten minutes immediately on waking. Make the bed back loosely rather than tightly tucked to allow airflow through the bedding. If multiple people share the bedroom, the moisture load is doubled and ventilation needs to be more energetic. North-facing bedrooms benefit from triple glazing more than other rooms because the cold-glass effect is strongest where solar gain is minimal.
Bathrooms
Bathroom condensation is concentrated and short-lived but intense. Run the extractor fan during showers and for 20 minutes afterwards. Open the window when leaving the room. Wipe down the inside of glass shower doors after use to remove standing water. If your bathroom extractor is an old fan that only runs while the light is on, consider upgrading to one with a humidity sensor or longer overrun timer; this single change often transforms bathroom condensation control.
Kitchens
Kitchen condensation is generated by cooking and washing. Cover pots when cooking. Run the extractor hood during cooking and for 15 minutes afterwards. Run the extractor over the dishwasher when it opens at the end of a cycle (the steam release is significant). Ducted extractor hoods that vent to the outside are far more effective than recirculating hoods that simply filter the air; on serious kitchen condensation problems, upgrading the extraction is often the best single intervention.
Living rooms
Living rooms generate less moisture than bedrooms or kitchens, so condensation here usually indicates either high humidity migrating from elsewhere in the home or specific cold-surface issues. Check the rest of the home’s ventilation first; persistent condensation in living rooms often improves dramatically when bathroom and kitchen extraction is properly used. For specific cold-window areas (large bay windows, north-facing aspects), targeted glazing upgrades may be appropriate.
New-build homes
New-build homes can be particularly prone to condensation in their first one to two years. Construction processes (plaster, screed, paint, mortar) introduce significant moisture that takes months to fully dry, and modern airtight construction reduces the natural ventilation that older homes provided. The right approach in the first 18 to 24 months is energetic ventilation: trickle vents fully open in winter, extractor fans used vigorously, and brief daily airing of all rooms. Once the construction moisture has fully dispersed, the home settles into normal operating conditions.
When windows are the problem
Some condensation patterns genuinely indicate that the windows themselves are at fault rather than just being the visible symptom of a wider issue.
Failed sealed units
Condensation inside the sealed glazing unit (where you cannot wipe it) means the unit has failed. The seals around the cassette have broken down and the gas fill has escaped. The unit no longer performs thermally and needs replacement. On a sound frame, the sealed unit alone can be replaced for £150 to £400. If multiple units have failed in the same property, the underlying frames are usually approaching the end of their service life and full replacement is usually the better answer.
Single glazing
Single-glazed windows have an internal surface temperature that drops well below the dew point of typical UK indoor air during cold weather, which means condensation on the inside of single glazing is essentially unavoidable in winter. Replacement with quality double glazing or addition of secondary glazing typically resolves the issue, alongside the standard ventilation and moisture measures.
Poorly installed frames
Condensation around the frame and on the surrounding plaster can indicate that the original installation did not properly seal or insulate the gap between the frame and the surrounding masonry. Cold air finds its way through the gap, the surrounding plaster runs cooler than the rest of the wall, and condensation concentrates around the perimeter. The fix involves resealing the frame externally with low-modulus silicone and ensuring the internal gap is properly filled with expanding foam and trimmed back to the plaster line.
Cold bridging
Cold bridging occurs where a thermally conductive material (often the metal lintel above an older window opening, or an aluminium frame without a proper thermal break) creates a path for heat to escape from the room. The surface around the cold bridge runs noticeably cooler than the rest of the wall, and condensation concentrates on it. Modern compliant windows with thermal-break aluminium or insulated uPVC frames eliminate frame-related cold bridging; lintel-related cold bridging needs separate addressing through internal insulation.
If your condensation is linked to failed sealed units, ageing frames or single glazing, it may be worth comparing practical repair options with replacement windows for your home. Modern windows can help improve thermal efficiency, reduce cold spots on the glass and support better ventilation when specified correctly.
Do double glazing, triple glazing, or shutters help?
The relationship between glazing upgrades and condensation is widely misunderstood. Here is the honest position.
Quality modern double glazing reduces condensation on the inside of the glass by keeping the surface warmer. Whole-window U-values of 1.2 to 1.4 W/m²K typically keep the inside glass surface above the dew point for normal indoor humidity levels in normal heated rooms. For most UK homes, this is enough.
Triple glazing reduces condensation further by keeping the inside surface warmer still. The improvement over quality double glazing is real but modest. Triple glazing earns its premium on rooms with persistent condensation despite good moisture management, and on north-facing rooms in colder regions where the cold-glass effect is strongest.
Plantation shutters and traditional fitted shutters can affect condensation in two opposing ways. When closed, they trap a layer of cooler air between the shutter and the window, which means the glass behind the shutter can run cooler than the room and accumulate more condensation overnight. Many shutter owners notice this in the morning when they open the shutters: the glass behind has condensation that the rest of the windows do not. The fix is not to remove the shutters but to ensure the room itself is well-ventilated, so the trapped air has lower humidity to begin with. Cellular blinds and heavy thermal curtains have similar effects to a lesser degree.
The honest framing for window dressings: they are not the cause of condensation, but they can amplify it where humidity is already high. Address the humidity and the issue largely resolves itself.
UK Building Regulations: Part F, Part L and trickle vents
The regulatory framework explains why modern replacement windows include features that older windows did not, and why this is good news for condensation control.
Approved Document L sets the minimum thermal performance for replacement windows. The current edition incorporates the 2023 amendments and applies to dwellings in England. The limiting whole-window U-value for replacement windows is 1.4 W/m²K, or a Window Energy Rating of Band B or better. Quality modern windows comfortably meet both routes, and the warmer inside surface temperature directly reduces condensation risk.
Approved Document F covers ventilation. Trickle vents (small ventilation openings in the frame) are now required on most replacement windows to maintain background airflow when the windows are closed. They are required even when the original windows did not have them, because modern airtight windows reduce the natural background ventilation that older windows provided. Trickle vents are unobtrusive in practice and are essential to the ventilation strategy that controls condensation.
Certification is handled by FENSA or CERTASS through registered installers under the Competent Person Scheme. A registered installer self-certifies that the work meets both Part L thermal performance and Part F ventilation requirements, and provides a certificate confirming Building Regulations compliance.
The practical implication: modern compliant replacement windows are designed to address the condensation problem at both ends (warmer surface temperature and adequate background ventilation). Removing or permanently closing trickle vents on new windows defeats the design intent and is a common cause of condensation problems in homes that have just had new windows fitted.
Cost guide: free fixes versus paid upgrades
The right amount to spend on condensation control depends on how severe the problem is and what is causing it. Working from cheapest to most expensive:
Free or low-cost fixes (£0 to £50): cover pots when cooking, take shorter showers, dry clothes outside, run extractor fans correctly, open trickle vents, air rooms briefly each morning, buy a hygrometer to monitor humidity. These measures resolve most mild to moderate condensation in most UK homes.
Mid-cost upgrades (£50 to £400): a quality dehumidifier (£150 to £400) for rooms where moisture management is genuinely difficult; an upgraded bathroom extractor with humidity sensor (£100 to £250 fitted); a window vac for daily wiping while you address the underlying cause; replacement of failed sealed units in otherwise sound frames (£150 to £400 per unit).
Higher-cost upgrades (£400 to £4,000): secondary glazing on listed or conservation properties (£300 to £600 per window); whole-house Positive Input Ventilation (PIV) systems (£500 to £1,500 fitted); replacement of single-glazed windows in selected rooms with modern compliant double glazing (£600 to £2,500 per window).
Major upgrades (£4,000+): whole-house window replacement (£6,000 to £20,000 depending on size and material); Mechanical Ventilation with Heat Recovery (MVHR) systems (£3,000 to £6,000 fitted); structural improvements to address cold bridging and wall insulation alongside the windows.
The honest framing: most UK homes resolve condensation comfortably within the free-to-mid-cost range, provided the diagnosis is correct. Spending major sums on glazing without addressing humidity and ventilation is the most common waste of money on this issue.
Homeowner decision guide
To turn the above into a practical action plan, work through the following sequence.
Try first: identify where the condensation is forming, buy a hygrometer to confirm humidity levels, address moisture sources (cooking, showering, drying clothes), use extractor fans correctly, open trickle vents, air rooms briefly each morning, and maintain stable background heating. For most UK homes, two or three weeks of these measures will significantly reduce or resolve the condensation.
Call an installer if: condensation is forming inside the sealed glazing units (failed unit, needs replacement); condensation is concentrated around frames and reveals (possible installation or thermal bridging issue); the windows are single-glazed or have early double glazing with failing seals (likely upgrade required).
Consider replacement if: multiple sealed units have failed in the same property; the windows are over 20 years old and showing age generally; the frames themselves are damaged (rot, warping, corrosion); cumulative repair costs are approaching half the cost of quality replacement; the home has other window-related issues alongside condensation (draughts, sticking, security concerns).
Consider mechanical ventilation upgrades (PIV, MVHR) if: the home is well-insulated and airtight (modern build or renovation), but condensation persists despite good moisture management; multiple rooms are affected and individual extraction is not enough; the property has had previous damp issues that need a whole-home solution.
Common mistakes when tackling condensation
Five mistakes appear repeatedly in homeowner attempts to resolve window condensation.
The first is closing trickle vents to save heat. The energy cost of leaving trickle vents open in winter is far smaller than the cost of running the heating harder to clear condensation later. Trickle vents are designed to provide background ventilation without significant heat loss; closing them defeats the design.
The second is treating new windows as a complete fix. Modern compliant windows reduce surface condensation by keeping the glass warmer, but they do not reduce the moisture in the room. Without addressing humidity and ventilation, the condensation often shifts to other surfaces (walls, mirrors, furniture) rather than disappearing entirely.
The third is wiping condensation as a permanent solution. Wiping the glass each morning removes the visible moisture but does nothing to address the cause. The same moisture forms again the next night. Wiping is appropriate as a short-term measure while you resolve the underlying issue, not as a long-term strategy.
The fourth is assuming a dehumidifier is the answer. Dehumidifiers are useful in specific circumstances (drying clothes indoors, bathrooms after extended use, persistent issues in single rooms), but they treat the symptom rather than the cause. Without addressing moisture sources and ventilation, a dehumidifier can run constantly without the home reaching healthy humidity levels.
The fifth is assuming external condensation indicates a faulty window. External condensation on cold mornings is a sign of efficient glazing, not a fault. It clears within hours of sunrise and requires no action.
Frequently asked questions
1. Why do my windows get condensation every morning?
Overnight, moisture from breathing accumulates in bedrooms while the windows cool. By morning, the glass surface is below the dew point of the room air and condensation forms. The fix is brief energetic ventilation on waking (open the windows wide for five to ten minutes), better background ventilation through trickle vents, and stable overnight room temperature.
2. Is condensation inside double glazing normal?
No. Condensation inside the sealed glazing unit (where you cannot wipe it) means the unit has failed and needs replacement. On a sound frame, the sealed unit alone can be replaced for £150 to £400. Multiple failed units in the same property usually indicate that the windows are approaching the end of their service life.
3. Is condensation outside windows a good sign?
Yes. External condensation on cold mornings is a sign of efficient glazing: the outer pane stays cooler than the surrounding air because the inside is well-insulated, allowing dew to form briefly. It clears within an hour or two and requires no action. New windows that show external condensation are working as designed.
4. Does double glazing stop condensation?
Not entirely, but it helps significantly. Quality modern double glazing keeps the inside glass surface several degrees warmer than older single or early double glazing, which means the surface stays above the dew point in normal conditions. It does not reduce the moisture in the room, so condensation may still form when humidity is high or ventilation is poor.
5. Do trickle vents stop condensation?
Yes, indirectly. Trickle vents provide background ventilation that allows moisture-laden air to escape and drier outside air to replace it. Without trickle vents, modern airtight windows can trap humidity in the home. Open trickle vents in winter rather than closing them; the energy cost is small compared with the cost of clearing condensation otherwise.
6. Should I leave trickle vents open in winter?
Yes. Trickle vents are designed to provide background ventilation without significant heat loss. Closing them in winter to save heat usually causes more problems than it solves, particularly on condensation. Open them in heated rooms; close them only briefly in unheated rooms or during exceptionally cold weather.
7. What humidity level should my home be?
Aim for 40 to 60 per cent relative humidity through the heating season. Above 60 per cent, the condensation and mould risk rises sharply. Below 40 per cent, the air can feel too dry, particularly on the respiratory system. A small hygrometer (£10 to £25) tells you what your actual levels are.
8. Is a dehumidifier worth it?
For specific situations, yes. Dehumidifiers are useful when drying clothes indoors, after long bathroom use, or in rooms where moisture management is genuinely difficult. They treat the symptom rather than the cause, so they work best alongside good moisture management and ventilation rather than as a substitute.
9. Should I wipe condensation off windows?
Yes, in the short term. Wiping prevents water running down to the frame and into the surrounding plaster, where it can cause longer-term damage. A window vac or microfibre cloth removes the moisture quickly. Wiping is a short-term measure, not a long-term strategy; address the underlying cause as well.
10. Can shutters or blinds make condensation worse?
Sometimes. Closed shutters and heavy thermal curtains trap a layer of cooler air between the dressing and the window, which can cause more condensation on the glass overnight. The fix is not to remove the dressing but to ensure room ventilation is adequate so the trapped air has lower humidity to start with.
11. When does condensation mean I need new windows?
When condensation forms inside the sealed glazing unit (sealed unit failure), when the windows are single-glazed and condensation is unavoidable in winter, or when the existing frames have multiple failures alongside condensation (draughts, sticking, visible age). Persistent condensation on otherwise sound modern double glazing indicates a humidity or ventilation issue rather than a window fault.
12. Is condensation worse in new builds?
Often yes, in the first one to two years. Construction processes introduce significant moisture that takes months to fully dry, and modern airtight construction reduces the natural ventilation that older homes provided. Energetic ventilation in the first 18 to 24 months helps the home settle into normal operating conditions.
13. What is the difference between condensation and damp?
Condensation is moisture from inside the home settling on cold surfaces. Damp is moisture coming into the home from outside, usually through failed roofs, gutters, walls or rising damp. Both can cause similar visible patterns (mould, staining), but the diagnosis matters because the fixes are different. Condensation requires moisture and ventilation management; damp requires structural repair to the source.
14. Do UK replacement windows need trickle vents?
On most replacement windows, yes, under Approved Document F. Trickle vents are required even when the original windows did not have them, because modern airtight windows reduce the natural background ventilation that older windows provided. They are unobtrusive in practice and contribute to better indoor air quality.
15. What is the best solution for period homes?
Period homes (Victorian, Edwardian, Georgian) often need a slightly different approach because the original construction was less airtight than modern homes. Engineered timber sashes with quality double glazing achieve good thermal performance while preserving period appearance. For listed buildings and conservation areas with restrictive Article 4 Directions, secondary glazing is often the right answer because it preserves the original windows entirely. Whichever route applies, address moisture management and ventilation alongside the glazing decision.