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A foggy window with water condensation formed on the glass
Image by AJ Jean from Unsplash

You know the scene. Tim and Lex stranded. Their breathing starts to quicken, the car windows begin to fog, and T-Rex attacks. Rose’s hand sliding down the steamy window in Titanic. Or when Uma Thurman puts a line through Kill Bill’s name on the fogged-up window at the swordmaker’s place.

Window condensation – it’s great for adding drama.

But you don’t want the drama of window condensation at home, so let’s look at some simple ways you can prevent condensation on your windows.

Three types of window condensation

Most homeowners in Perth, Bunbury and around Western Australia would have all encountered window condensation at some stage.  It might seem harmless, but if left unchecked it can cause damage to your home.

Don’t want the drama of condensation causing damage? But what you can do about it? The answer depends on the type of window condensation you are dealing with.

  1. Interior window condensation

Interior window condensation is the main antagonist of this article. It forms indoors and is characterised as foggy windows that you can draw on with your finger.

  • Seen as droplets of water on the inside of the window
  • Does not indicate there is anything wrong with your windows
  • Wipe away condensation when you see it
  • Reduce humidity in your home to prevent it occurring
  • Can cause damage if excessive
  1. Exterior window condensation

Exterior window condensation occurs when the exterior surface of a window is cooler than the dew point of the surrounding air, resulting in moisture droplets forming on the outside of the glass.

  • Seen as droplets of water on the outside of the window
  • Does not indicate there is anything wrong with your windows
  • Wipe away condensation or let it evaporate naturally
  • Can appear even on energy efficient windows
  1. Window condensation between your double glazing

Condensation between double glazing panes can occur when there is a breach in the seal of the window, allowing moisture to enter and become trapped between the two panes of glass.

  • Seen as moisture in between the two panes of glass in an insulated window
  • Indicates a problem with the airtight seal on your IGU (Insulated Glass Unit)
  • Moisture does not tend to evaporate due to limited airflow between the two pieces of glass
  • Window replacement is the ideal solution


  • Condensation on windows occurs when the air in the room is warm and humid, but your windows are cool
  • Droplets of water form on the inside of your windows – not to be confused with leaking windows
  • Commonly occurs in winter, and in rooms with insufficient ventilation
  • Can be prevented by improving ventilation in the room to reduce humidity
Modern bathroom setting with an awning window that has been opened for ventilation.

What is interior window condensation?

Common during winter and in rooms with insufficient ventilation, interior window condensation is noticeable when your windows become foggy and droplets of water form on them.

This happens because the temperature of your windows are cooler than the humid, warm air that is in your room.

As the warm air comes into contact with the colder surface of your windows, the air cools and its moisture condenses on your windows.

What causes interior window condensation?

Condensation is usually first noticed on windows and glass panel sliding doors because they tend to have the lowest temperature of any of the visible surfaces in your house. Because of this they are often singled out as the cause of the condensation, but in reality they act as a warning sign that humidity may be too high in your home.

Indoor air humidity can be caused by everyday living:

  • Putting the kettle on to boil
  • Airing clothes to dry inside your home on rainy days
  • Having hot showers
  • Fish tanks and indoor house plants
  • and even breathing!

Consider interior window condensation as a symptom and not a cause of high humidity in your home.

Is interior window condensation bad?

Condensation on windows in itself is not bad. It’s simply a tell-tale sign that the humidity in your home may be too high.

High humidity in your home can lead to health issues and maintenance problems:

  • Bacteria and mould can take hold in humid conditions
  • Spending too much time in a high humidity environment may cause respiratory problems or trigger allergies
  • Excess moisture from high humidity can cause peeling wallpaper, damp patches, stains and discolouration of your walls and ceilings, and can even damage window sills if the water droplets continuously pool there

Controlling the humidity levels in your home is important for creating a comfortable living environment, saving on energy costs, and reducing health and maintenance related issues.

A little fog on your windows is OK, but you should investigate the cause and take corrective action if you notice excessive condensation on your windows and cold walls.

An infographic showing the surprising amount of water our daily activities add to the air. For example, breathing adds 0.5 litres per day, and cooking can add 3 litres per day!

Source: AGWA Technical Fact Sheet, Condensation Management

How to stop interior window condensation

The best way to control condensation is to keep the relative humidity low. Following are several easy steps you can take to reduce moisture in your home and stop window condensation.

Seven tips to prevent interior window condensation

  1. Open windows slightly to improve ventilation
  2. Close bathroom doors when having a shower to prevent moisture in the air from escaping into colder rooms
  3. Use exhaust fans during and after showers and baths, and when cooking
  4. Ensure exhaust fans are vented externally and not just into your roof cavity
  5. Keep your windows open when using a clothes dryer, or dry clothes outside in a sunny spot
  6. Cover up your aquarium to prevent excess moisture in the air
  7. Ensure your windows are correctly and adequately sealed

The Australian Glass & Window Association (AGWA) also provides useful information on managing window condensation.