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Condensation on windows

How to stop condensation on windows (and what causes it)

Condensation on windows is an inconvenience in colder months, but if left untreated it can lead to serious problems and shouldn’t be ignored.

Condensation on windows

How to stop condensation on windows

Condensation can damage windows and furniture, cause mould and be detrimental to health.


Getting to the real cause of the problem is the only way to stop condensation from forming on windows and on walls inside your home. The first step is figuring out what is causing the excessive moisture in your home.


Keep reading and we will share with you:

  • What causes condensation
  • Why condensation is bad for health
  • How to stop condensation

We will also answer a few common questions at the end.

What causes condensation on windows

What causes condensation on windows


Condensation is created by excess moisture in the air that forms on cold surfaces. Usually on windows when it’s colder outside than inside.


The air around us contains lots of microscopic droplets of water that we can’t see. When it’s more humid, the water content becomes more concentrated and more likely to ‘condense’ on surfaces.


Imagine a glass of iced water on a hot day that looks like it’s sweating. This is a result of the moisture in warm air colliding with the cold surface of the glass.


In warm air, the molecules are spaced far apart and this ‘holds’ the moisture, but in cool air, the molecules come together. When the molecules become close enough together, they merge into visible liquid. This is known as the 'dew point'.


At the dew point, we can see the drops of water form on a surface. Think of:

  • Condensation on a mirror after a shower
  • Kitchen window steamed up when cooking
  • Moisture on windows when drying clothes indoors

Condensation doesn’t just form on windows, it can form on any cold surface. Especially in areas where moisture can become trapped:

  • Windows that have blinds or curtains
  • Behind large furniture against a cold wall
  • Inside a fitted wardrobe on an external wall
Windows should not have condensation between the panes

Evererst windows are built to last with long-lasting guarantees

How can condensation damage windows?

How can condensation damage uPVC windows


Sitting water will eventually be detrimental to any surface it collects on, even waterproof surfaces. Think limescale build-up and mould.


While uPVC windows are built to withstand water, excessively wet seals combined with strong direct sunlight can cause them to dry and crack from constant expansion and contraction.


Wooden frames are especially susceptible to damage:

  • Paint and varnish can peel
  • Wood trim will dry and crack

How can condensation damage wooden windows


The main concern from standing water and moisture is mould. If left untreated mould will damage and discolour uPVC and wood.


More importantly, mould is exceptionally bad for our health.


Condensation and black mould

The real issue with condensation is that it can lead to black mould.


Patches of black mould around windows, on doors and on walls doesn’t just look unsightly, it could be making you seriously ill.


The main symptoms from mould are:

  • Stuffy nose
  • Wheezing
  • Red or itchy eyes
  • Skin rashes and itching

WHO also reports that mould can contribute to:

  • Asthma
  • Allergic rhinitis
  • Hypersensitivity pneumonitis
  • Allergic alveolitis
  • Chronic rhinosinusitis
  • Allergic fungal sinusitis.

There is more (non proven) evidence that acute idiopathic pulmonary haemorrhage causes memory loss and lethargy for infants.


Undoubtedly, mould is bad news and needs to be dealt with.


Any mould that appears should be carefully cleaned and removed and then preventative measures put in place to get rid of condensation.


How to stop condensation on windows

The main cause of condensation is a lack of ventilation. The remedy is to improve ventilation to help equalise humidity inside and outside a property.


Once upon a time, houses had badly-fitted windows, doors, chimneys and air vents that allowed for the circulation of air.


Homes have become considerably more energy-efficient over the last thirty years and this has resulted in a lot of houses becoming sealed units that trap moisture in the house.


Although we have become better at retaining heat, we have lost natural ventilation in our homes.


Getting rid of condensation on windows for good will involve:

  • Improving ventilation
  • Reducing moisture
  • Installing double or triple glazed windows

How to improve ventilation to reduce condensation

There are a few options to improve ventilation in your home:


Airflow system

Many new apartments are built with internal airflow systems to combat the problem. These systems use a network of ducts in the ceiling to extract and exchange air from the outside to inside.


This maintains air circulation and a humidity balance within a property that is well-sealed.


Retrofitting a ventilation system in a house is invasive and expensive and not always possible in older houses.


PIV Unit

For an easier to install solution, Positive Input Ventilation (PIV) units can be fitted in areas that produce excessive moisture. Such as kitchens and damp basements.


The unit extracts the humid air from inside the house and draws in ‘dry’ air from the outside. This exchange of air helps to maintain the humidity balance.


Extractor fan

Having sufficient extraction in a bathroom is essential to reduce the excessive humidity produced from showers. Some fans have humidity control and will allow the fan to operate automatically if the humidity level increases above a set level.


Kitchens also need good extraction systems for cooking to remove smoke, smells and moisture.


Air vents/bricks

Air bricks often get blocked to stop draughts, but they do work to keep an area ventilated. A simple vent will ensure the humidity is managed in a room, but this does have the result of energy efficiency being reduced. For this reason, air bricks are not as popular as they used to be.


Air vents in windows do work to help with ventilation and stop condensation on the window. They can be installed on most windows.


Opening windows

Your grandmother probably used to open the doors and windows every morning to ‘air’ her home. There is nothing better than allowing fresh air to circulate through a space to keep it ventilated, remove stale air and smells and to reduce moisture in the house.


Traditional windows were used to provide effective ventilation which was essential when most homes were heated by fossil fuels.


Sash windows were designed to allow for the bottom and top to be opened that would draw air in and out providing effective ventilation.


Bay windows were designed to have two casement windows on either side to allow superior draw and ventilation.


Transom windows above a door were designed to increase airflow around a property to move heat around internally and to ventilate.


Modern windows all have multi-point lock settings to allow them to be left open securely for ventilation. This is one of the simplest and easiest ways to keep your home ventilated and avoid condensation.

Reducing moisture to reduce condensation

In combination with ventilation, reducing moisture is also essential to stop condensation. The average household produces a considerable amount of water vapour each day just from normal living activities.

CookingUp to 3 litres per day
Clothes washing0.5 litres per wash
Showers and baths1.5 litres per person
Washing dishes Up to1 litre per day
Un-vented clothes drying5.0 litres per load
Breathing, active adult0.2 litres an hour per person
Breathing, adult asleep0.02 litres an hour per person

Houseplants and pets also contribute to water moisture in the air and condensation.


The biggest causes of excess moisture that causes condensation

All of these areas should be addressed to try and minimise the impact they have on contributing to humidity in the house:

  • Cooking, boiling pans and kettles
  • Showers and hot taps
  • Washing machines and tumble dryers
  • Drying clothing on radiators or indoor airers
  • Large houseplants
  • Wet logs stored for wood burners
  • Unfound water leaks in cavities or under floors
  • Rising damp in basements and ground-level buildings
Is it time to consider new double glazing windows?

Everest windows are built to last with long-lasting guarantees

Install double glazing to reduce condensation

Install double glazing to reduce condensation


The reason we see so much condensation on single glazed glass is that the glass is susceptible to cold and stimulates the dew point from the water vapour in the air.


Double glazing helps to reduce condensation because the glass is not as cold as single glazed. The air gap inside the double glazing sandwich helps to keep the internal pane of glass closer to room temperature. This difference in temperature is enough to stop the water vapour from reaching the dew point and forming condensation on the glass.


Double glazing can’t eliminate condensation entirely, so following a combined approach of windows, ventilation and reduced moisture is the only way to completely get rid of condensation.


Do dehumidifiers stop condensation on windows?

For internal spaces where you can’t open the window, or for excessive damp and moisture, a dehumidifier is an option.


Dehumidifiers work by extracting excess moisture from the air and collecting this in a tank that you would empty. It’s always surprising just how much water they can extract. However, always keep the windows closed when using as they will try to draw in moisture from the outside.


Dehumidifiers are a good idea for:

  • Drying clothes
  • Drying out an attic or cellar with a damp problem
  • Drying out after a leak or flood

It is important to note that dehumidifiers are only treating the symptom and it is far better to treat the cause for a long term solution.


Condensation on the inside of windows


Condensation on the inside of windows

If you have double or triple glazed window, condensation between the panes of glass inside the glazed unit means that the seals have failed on the glazing unit.


Double glazed units actually hold a low level of moisture internally. To stop the moisture forming on the glass inside, the unit also has crystalline desiccant (like what you find in a new bag or shoes) contained in the spacer bar. The desiccant draws the moisture out of the air gap and keeps the internal space between the panes dry.


Internal condensation happens when the seals on the sealed unit begin to fail and more moisture is drawn into the unit. The desiccant becomes saturated and can no longer hold moisture and as a result, condensation forms inside the unit.


Condensation on new windows

You should never experience condensation in between the panes of new windows.


If you do experience internal condensation there is a problem with the seals and it should be covered under a manufacturer’s warranty.


Condensation on the outside of windows in the morning

In the early morning during summer, you can see condensation appear on the outside of the window. This means that the air temperature outside is humid and warming quickly, but the glass is still cold. This is perfectly normal and will clear quickly as the sun warms the glass.


Condensation on bedroom windows

Two adults sleeping can expire up to half a litre of water overnight. This is why, in the morning, bedroom windows can have condensation. The best way to control this is to have the window on a vent or the bedroom door open with another window open for ventilation. If you have problems with condensation, speak to us about your current windows to see if new double glazed windows would help.

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