Condensation on windows: How to stop and prevent it inside, dehumidifier, anti condensation paint - causes

As we approach the final month of 2023, daylight hours shorten, nights lengthen and temperatures plummet. With the colder weather settling in, steamed-up windows become a common issue in both households and vehicles.

Fogged windows, whether in your car or at home, not only mar aesthetics but also pose health risks by fostering the growth of black mould.

Here's a comprehensive guide to condensation, covering its causes and preventive measures you can take.

What causes condensation on the inside of windows?

Condensation forms when warm, moist air comes into contact with a colder surface, such as a window pane. When warm air meets the cooler glass surface, it cools down, and its ability to hold moisture decreases.

This leads to the moisture in the air condensing into water droplets on the window surface. When the indoor air is warm and humid and the outside temperature is cooler, the window surface becomes cold.

The greater the difference in temperature between the inside and outside, the more likely condensation will occur. Higher humidity levels indoors increase the amount of moisture in the air, making it more likely to condense on cooler surfaces like windows.

Poor insulation or inadequate ventilation can contribute to higher humidity levels indoors, increasing the chances of condensation.

What causes condensation on the outside of windows?

Condensation on the outside of windows typically happens when the temperature of the glass surface drops below the dew point of the surrounding air. It occurs more commonly in certain weather conditions.

If the outdoor air is very humid, and the temperature of the window surface drops, it can cause condensation on the outside of the window.

This happens similarly to how condensation forms on the inside but in reverse: warm, moist air comes into contact with a cooler surface (the window), causing the moisture in the air to condense.

Sudden drops in temperature can cause condensation on the exterior of windows, especially in situations where the window surface cools down quickly due to the weather conditions, such as during a sudden temperature drop at night.

During certain weather conditions like cool nights after a warm day, dew can form on surfaces including windows. Dew forms when the temperature drops, and the surface cools below the dew point, causing moisture in the air to condense on the surface.

Does condensation lead to black mould?

Condensation can contribute to the growth of black mould under certain conditions. Mould thrives in environments with excess moisture, warmth, and organic matter to feed on.

Condensation provides the necessary moisture for mould growth, especially on surfaces like windowsills, walls or other areas where moisture collects.

If condensation regularly forms on windows and isn't addressed, the moisture can seep into surrounding surfaces, creating an environment conducive to mould growth.

Black mould, specifically Stachybotrys chartarum, is known to grow in damp, humid environments and can appear on surfaces that remain consistently moist.

How can I prevent condensation on the inside of windows?

Reducing condensation on the inside of windows involves managing the factors that contribute to excess moisture in the air and minimising temperature differences between the indoor air and the window surface.

Ensure good airflow throughout your home. Use exhaust fans in kitchens and bathrooms to remove moisture. Opening windows periodically, especially when cooking or showering, can also help.

If indoor humidity levels are consistently high, a dehumidifier can help reduce moisture in the air. Improve the insulation around windows to reduce the temperature difference between the indoor air and the window surface. Weather stripping, caulking or adding storm windows can help.

Double or triple-pane windows are more insulated and can reduce the likelihood of condensation by keeping the indoor glass surface closer to room temperature, and silica gel, moisture-absorbing crystals or desiccants placed near windows can help absorb excess moisture.

Use a hygrometer to monitor indoor humidity levels and take action if levels are consistently high. Keeping a more consistent indoor temperature can help minimise temperature differences that lead to condensation.

How do I prevent condensation on the outside of windows?

Condensation on the outside of windows typically happens when the temperature of the glass surface drops below the dew point of the surrounding air. It occurs more commonly in certain weather conditions.

If the outdoor air is very humid, and the temperature of the window surface drops, it can cause condensation on the outside of the window.

This happens similarly to how condensation forms on the inside but in reverse: warm, moist air comes into contact with a cooler surface (the window), causing the moisture in the air to condense.

Sudden drops in temperature can cause condensation on the exterior of windows, especially in situations where the window surface cools down quickly due to the weather conditions, such as during a sudden temperature drop at night.

During certain weather conditions like cool nights after a warm day, dew can form on surfaces including windows. Dew forms when the temperature drops, and the surface cools below the dew point, causing moisture in the air to condense on the surface.

Should I wipe condensation off myself?

Wiping condensation off windows is a good practice, especially if it's a recurring issue.

Regularly removing condensation helps prevent moisture from seeping into surrounding surfaces and reduces the likelihood of mould growth or potential damage to window frames or sills.

Wipe the moisture off using a clean, dry cloth or towel - microfiber cloths work well for this purpose. Don't forget to wipe down the window sills and frames where moisture might accumulate. Keeping these areas dry helps prevent mould growth and potential damage.

After wiping the condensation, it's a good idea to improve ventilation in the room by using fans or opening windows to allow the moist air to escape.

Make wiping condensation a regular part of your maintenance routine, especially during periods of high humidity or when you notice significant condensation buildup.