As the temperatures drop and we spend more time indoors, many homeowners begin to notice a familiar winter nuisance: condensation forming on the inside of their windows. While it might seem harmless—just a bit of water on glass—persistent condensation can lead to mould growth, damp patches, and even long-term damage to window frames and surrounding walls.
Here are the most common causes of winter window condensation and why it happens.
1. Warm Indoor Air Meets Cold Window Surfaces
Condensation occurs when warm, moisture-filled air comes into contact with a cold surface—in this case, your windows. During winter, indoor heating makes the air inside your home warmer than the air outside. Warm air can hold more moisture, but once it hits a cold pane of glass, the air cools and releases this moisture as droplets.
Homes with older single-glazed or poorly insulated windows experience this more intensely, as the inner surface of the glass becomes much colder.
2. Everyday Household Activities Increase Moisture Levels
Modern homes are excellent at keeping heat in—but that also means they often trap moisture. Common daily activities add surprising amounts of water vapour to the air:
- Cooking and boiling water
- Showers and baths
- Drying clothes indoors
- Breathing and sleeping (a family can release litres of water vapour a day!)
In the winter, we tend to keep windows closed, reducing natural airflow. Without proper ventilation, the moisture has nowhere to escape and ends up collecting on the coldest surfaces—typically windows.
3. Poor Ventilation and Airflow
Condensation is far more common in rooms with limited ventilation, such as bathrooms, kitchens, and bedrooms. When air becomes stagnant, humidity builds up quickly.
Homes without adequate extractor fans, trickle vents, or regular airflow are especially prone to condensation. Even energy-efficient homes—which are designed to be airtight—can suffer from moisture issues unless ventilation is well-managed.
4. Cold Spots and Insulation Problems
Sometimes condensation forms around window edges, on frames, or near exterior walls. This can indicate thermal bridging or insulation gaps, where cold enters the home more easily. These cold spots cool the surrounding air, causing moisture to settle there first.
Upgrading insulation, improving glazing, or adding thermal curtains can reduce these problem areas.
5. High Indoor Humidity Levels
Many homes simply run too humid in the winter. Ideal indoor humidity levels are 40–60%, but winter levels often rise above this due to heating, moisture-producing activities, and reduced ventilation.
When humidity climbs, condensation becomes inevitable—especially during the coldest mornings and evenings.
Condensation on windows during winter isn’t just a seasonal annoyance; it’s a sign that your home’s air, insulation, or ventilation system may need attention. By understanding the causes—ranging from everyday activities to structural factors—you can take proactive steps to protect your home from damp, mould, and costly long-term damage.
If you’d like help reducing condensation or improving your home’s ventilation or glazing, 23 Doors is always here to advise and support.
