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Managing condensation: Tips and techniques

Updated: Apr 25

During the winter months, you might find that even with the best new windows and doors, condensation can form around the frame. This blog post seeks to address some of the issues that cause condensation and how to manage it.

Condensation occurs when warm, moisture-laden air comes into contact with a colder surface, such as a glass window, causing the water vapour in the air to cool and transform into liquid water droplets. This process is similar to how dew forms on grass or moisture forms on a cold drink.

The air around us naturally contains varying amounts of water vapour, which is invisible to the naked eye. The capacity of air to hold water vapour increases with temperature, meaning warm air can hold more moisture than cold air. When warm indoor air comes into contact with a cold window, the temperature of the air next to the window drops, causing the water vapour in that air to reach its dew point — the temperature at which it condenses into liquid water.

Condensation is more likely to occur in certain situations, such as during colder weather or in rooms with high humidity levels. Activities like cooking, showering, or drying clothes indoors can release a significant amount of moisture into the air, increasing the likelihood of condensation on windows. Additionally, inadequate ventilation or insulation in a building can contribute to higher humidity levels, exacerbating the condensation issue.

Condensation can have several effects. It can obscure the view through the window, create water droplets that may run down the glass and cause water damage to window boards or surrounding surfaces, and potentially lead to mould or mildew growth if the excess moisture isn't properly addressed.

To reduce condensation on windows, it's important to control the humidity levels within your home or building. Here are some tips:

1. Use ventilation: Ensure that rooms with high moisture levels, such as bathrooms and kitchens, have proper ventilation systems like extractor fans. Opening windows periodically to allow fresh air circulation can also help.

2. Use dehumidifiers: In areas with high humidity, using dehumidifiers can help remove excess moisture from the air.

3. Insulate windows: Using high performance windows can help keep the glass surface warmer and reduce the temperature difference between the indoor air and the window pane.

4. Monitor indoor humidity: Use a hygrometer to measure the humidity levels in your home. Ideally, indoor humidity should be maintained between 30% and 50%.

By managing the humidity levels and improving insulation and ventilation, you can minimise or even eliminate condensation on windows, ensuring a more comfortable and visually clear environment.

What about condensation on the outside of the windows?

Condensation on the outside of windows occurs when the surface of the window is colder than the dew point of the air outside. This phenomenon typically happens during specific weather conditions.

In general, condensation forms when warm, moist air comes into contact with a cold surface, causing the water vapour in the air to cool and turn into liquid water droplets. However, when condensation appears on the outside of windows, it is the result of a different process.

During certain weather conditions, such as cool or cold mornings, evenings, or during periods of high humidity, the temperature of the outside surface of the glass can drop below the dew point of the air outside. The dew point is the temperature at which the air becomes saturated and can no longer hold all the moisture it contains. When the dew point is reached or exceeded, excess moisture in the air condenses into water droplets on any available cool surfaces, including the outer surface of windows.

The glass acts as the cold surface that causes the water vapour in the air to cool and condense into liquid water droplets.

Condensation on the outside of windows is harmless and often a temporary occurrence. It actually shows that very little heat is escaping through the glass, so is seen as an indicator of a high performance window. It tends to disappear as the temperature rises or as the humidity levels change.

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