Why do my windows run with condensation every morning?

Your windows run with water in the morning because warm, moist air indoors is meeting the coldest surface in the room and turning back into liquid. Window glass is usually where you see it first. A little on a cold morning is normal. Streaming windows every day usually mean there is more moisture in the air than the room can get rid of, the room is getting too cold, or both. Most of the fixes are simple, and if they do not work, that tells you something useful too.

What is happening on the glass

Indoor air always carries some water as invisible vapour. When that air cools to its dew point, it cannot hold all of it, and the extra settles as droplets on any surface at or below that temperature. The dew point shifts with the humidity, the air temperature and the temperature of the surfaces around it.

Glass is where you notice it, but the same thing happens on other cold surfaces, such as walls, room corners and the low points behind sofas and wardrobes. GOV.UK guidance describes condensation as the most common form of damp, and the Society for the Protection of Ancient Buildings (SPAB) notes that it occurs mostly in winter.

Why it builds up overnight

A closed bedroom gathers moisture from the people sleeping in it. People produce moisture, so the more people in a home, the more there is. RICS, the surveyors' professional body, explains that when indoor temperatures drop or humidity is high, water vapour turns into droplets on the coldest surfaces in a room. If the heating goes off at night and the windows are shut tight, you have both at once.

Other things that push moisture levels up include:

• drying clothes over radiators
• cooking without lids on pans, or using a cooker hood that only recirculates air back into the kitchen
• showering or bathing with the door open and no window or extractor fan in use
• a tumble dryer that is not vented outside
• poor ventilation, especially in kitchens and bathrooms
• not heating the home enough
• more people living in the home

That list is not about blame. GOV.UK guidance says everyday tasks like cooking, bathing and drying laundry will always produce indoor moisture, and that it is totally unreasonable to blame damp and mould on lifestyle choices. The deeper reasons are usually the building, the ventilation, the heating or poor energy efficiency. Small changes to your routine help, but they sit alongside fixing those things, not instead of them.

Is it just a nuisance?

Wiped up promptly, a bit of condensation on glass does little harm. Left day after day, it can lead to damp and mould. RICS says mould typically forms around windows, on external walls and on ceilings close to external walls. If any part of your home has mould growth, a musty smell, or is not dry to the touch, RICS says you should investigate.

GOV.UK guidance says that damp and mould primarily affect the airways and lungs, but they can also affect the eyes and skin. It adds that everyone is vulnerable to the health impacts of damp and mould, but people with certain health conditions, children and older adults are at greater risk of more severe health impacts.

What you can do about it

The aim is simple: put less moisture into the air, let more of it out, and keep surfaces warm enough that it does not settle on them.

• Ventilate little and often. RICS says windows do not need to be open all the time; about five minutes for every hour you are in a room is enough. Trickle vents or the secure window latch let in a small, steady amount of air.
• Use extractor fans every time you cook, bath or shower. Opening a window does not always work when it is humid outside, so fans matter too. Check they work and clean them regularly.
• Close kitchen and bathroom doors while they are in use, with a window open in there.
• Put lids on pans, dry washing outdoors when you can, and make sure a tumble dryer is vented outside or has a condensate system.
• Keep the heat steady. RICS suggests keeping internal heat levels ideally between 18C and 21C. SPAB says heating run constantly at a low level, rather than in bursts, helps keep surfaces above dew point.
• Leave a gap between furniture and external walls, and do not block air vents in bedrooms and cupboards.
• Wipe the glass and sills each morning with a dry cloth. RICS says this helps prevent mould growth.

Dehumidifiers can help in some rooms. SPAB says they can reduce condensation effectively when rooms are warm and damp, but are of limited benefit when rooms are cold and humid.

If money is tight and you can only heat yourself rather than the house, RICS points out that your home still needs ventilation. It also notes you may be entitled to government help if you are finding it difficult to heat your home.

Wiping windows each morning is worth doing, but if you are wiping every day all winter and nothing is changing, treat that as a reason to look for the cause.

When condensation is not the whole story

Sometimes the window is just where extra moisture shows up. GOV.UK guidance says there may be multiple causes, and that leaks or water getting in from outside can make condensation worse. RICS gives an example of a home where water coming up through a solid floor raised humidity and led to condensation as a secondary problem.

Some things anyone can check, ideally on a rainy day:

• leaking or blocked gutters and downpipes
• broken sealant or mortar around windows and doors, or windows that do not close fully
• cracked render or poor pointing on outside walls
• ground levels raised up against the walls
• plumbing leaks under baths or broken seals around showers

If you have cut down moisture, ventilated and kept the heat steady and the windows still stream, mould keeps coming back, or damp patches appear away from the windows, it is sensible to ask an independent building surveyor with experience in building pathology to find the cause. RICS advises asking for a Joint Position Statement 2022 (JPS22)-compliant inspection, which gives an opinion from someone without a commercial interest in selling you a product. Be cautious of anyone who relies only on a damp meter, especially on hard walls and solid floors.

If you rent, report condensation and mould to your landlord or managing agent promptly. GOV.UK guidance says landlords should identify and tackle the underlying causes, including building deficiencies, inadequate ventilation and condensation, and that simply removing surface mould will not stop it coming back.

Cold stone walls and sealed-up windows in Yorkshire and Lancashire

Many older stone terraces and back-to-backs were built to let moisture escape. SPAB explains that old buildings historically lost moisture through open fires and loose-fitting doors and windows. Double glazing, heavy draughtproofing and blocked flues or air bricks all reduce that ventilation. If your windows started streaming after new windows went in or a fireplace was blocked up, that change may be part of the picture.

Replacing old windows does not have to make things worse, but RICS reminds owners that modern windows have tighter seals, so you may need more ventilation, and new glazing will not reduce the amount of moisture in the house. GOV.UK guidance notes that under building regulations, all replacement windows are required to have trickle vents.

Solid stone walls need particular care. SPAB says damp readings on plaster, especially on north-facing walls, are commonly mistaken for rising damp and used to justify unnecessary damp-course work, when condensation is the real source. RICS adds that in older buildings with solid walls, damp-proofing measures may not be appropriate and may make damp worse, and that modern cement mortar or render can trap moisture in walls. So before spending on damp-proofing a cold gable wall, rule condensation in or out first.

This page gives general information, not legal or medical advice. For your own situation, use the organisations listed under "Where this comes from" at the foot of the page.