What causes condensation, and how can you reduce it?

When water droplets form naturally on the inside of your windows or walls, this is condensation. Signs that you have significant condensation in your house include streaming windows, damp walls, peeling wallpaper, black mould growth, and a musty smell. Learning what causes condensation will help you maintain a moisture-free home and ensure you don’t suffer any related health issues.

Condensation is formed when moist, warm air cools quickly. For example, if the air comes into contact with a cool window.

So how is condensation linked to humidity? The warmer the air, the more water vapour it can hold. When air at a constant temperature can’t hold any more water vapour, the humidity is at 100%. If that air’s temperature drops, it can no longer hold that amount of moisture, and so droplets form. This is how condensation occurs.

What causes condensation in my house?

Once you’ve noticed condensation inside your home, the next step is to identify the cause. Any activities that allow water to evaporate will increase humidity and lead to condensation. These include:

• Boiling liquids when cooking
• Steam ironing or ironing damp clothes
• Drying clothes indoors
• Wet/dry vacuum cleaning or washing floors
• Tumble drying without working ventilation
• Showering or bathing
• Decorating e.g. stripping wallpaper with water
• Plumbing leaks e.g. from washing machines

On average, a family of four produces up to 13 litres of water vapour per day in the ways listed above. It all has to go somewhere, and can end up as condensation on the walls and on surfaces around the house – unless the moisture-filled air is expelled from the property.

Once you know what causes condensation, you can learn how to maintain moisture levels and prevent the droplets from forming.

Why is condensation worse in the winter?

At the end of autumn and the start of winter, condensation is more likely to appear. This is because colder windows and walls will cool the warm air indoors faster.

However, two homes heated to 24C with 60% humidity may experience very different levels of condensation. In a home with efficient double glazing and insulation, it might not form at all. But a home with single-glazed windows and poor insulation will probably experience a lot of condensation.

Comfort temperature
Between 22C and 27C is the so-called temperature that we feel most comfortable in. This is usually what most central heating systems are set to.

Reducing activity that creates water vapour and increases humidity levels would go some way to reduce condensation. However, that isn’t always realistic. So, what practical steps can you take to prevent condensation in the home?

1. Install air extractor units

Extractor fans in bathrooms and kitchens expel humid air before it circulates, so they’re great at fighting the causes of condensation. Keep the doors closed when using them, as this will lower the humidity in other rooms. Check that your air extractors are working and turned on when you cook or shower, and preferably for five minutes afterwards.

Make sure you get a cooker hood that vents externally rather than a recycling one. Recycling extractors remove smells and particles, but not vapour from the environment.

2. Open your windows

One of the easiest ways to stop condensation is by opening some windows, especially in rooms with high humidity. Opening a window for just a few minutes may be enough to reduce humidity levels enough to reduce condensation in the home.

What causes condensation will depend on your property and how you use it, but by opening windows, you give excess moisture a way to escape.

3. Open trickle vents

Trickle vents built into some windows, allowing indoor and outdoor air to exchange constantly. It can sometimes be tempting to close these vents to reduce draughts in winter, and some people even try taping over them. However, the air coming in isn’t a draught from faulty insulation, but a deliberate feature designed to affect what causes condensation – warm air hitting cool surfaces.

Not all windows have trickle vents. You can retrofit them into most uPVC and wooden window frames, but this requires specialist knowledge.

4. Dry clothes outside

When drying clothes, try to hang them outside when possible. When it rains and you have to dry your clothes indoors, keep nearby windows open and close the door to other rooms. If you have a tumble dryer, make sure it vents externally and isn’t filling your home with humid air.

Remember that drying clothes on radiators means that your central heating system will have to work harder. This is because your clothes will act as a barrier against effective heat transfer.

Tip: Most modern washing machines have an option for a spin-only cycle. This usually removes moisture by spinning the load at a high speed without using additional water.

5. Replace your low-performing windows

Double and triple-glazed windows are much better at reducing condensation than their single-glazed counterparts. They include a sealed space between the panes of glass, which consists of either a vacuum, or an insulating gas like argon. This reduces heat transfer, so the outer pane stays cool while the inner one stays closer to the temperature indoors.

If there’s condensation inside your double-glazed windows, it means the unit has ‘blown’ and the gas has escaped – likely through a damaged seal. The only way to prevent condensation in this case is to replace the unit.

6. Install cavity wall insulation

When looking at how to prevent condensation, it’s worth looking beyond glazing. Droplets can form on other surfaces too, like on the walls of a property. Without good insulation, the cold outside temperature will seep through external walls, and make internal walls cold as well. Then when the humid air comes into contact with the cool wall, the vapour turns into condensation.

The empty space between inner and outer walls insulates the home to some degree, but far it’s better to fill this void with insulation. Homes built in the 1920s and onwards will likely have cavity walls, but newer homes tend to come with insulation as standard.

A/C units work by sucking in warm air and then cooling it. When the humid air passes through, the vapour condenses onto an evaporating coil and then drains away. As a result, air conditioners can help to reduce condensation, but there are more cost-effective solutions available.

Example: When you sit in a car on a cold day, your breath condenses on the windows. The air conditioner removes moisture from the air as it cools, so there’s less of a temperature difference between the air and the windows.

A dehumidifier can be effective for rooms that constantly suffer from condensation, damp and high humidity levels. This appliance draws in the humid air and releases it as dry air – taking much of the moisture away. Dehumidifiers use a lot of energy though, so it’s worth trying a more long-term solution.

Tip: Getting rid of condensation shouldn’t increase your energy bills. When looking at what causes condensation inside the home and how to prevent it, try to find solutions that use as little energy as possible.

Some specially designed paints can prevent the build-up of condensation on walls, with the paint acting like an insulating layer. However, the level of success will depend on the wall and the insulation behind it.

When looking to resolve what causes condensation, you could take the time to redecorate. Why not use anti-condensation paint to spruce up your bathroom, or any other room that suffers the most from condensation?

While obviously not a solo solution, some common houseplants can help with humidity levels when used with other methods. Plants that thrive in humid environments and draw moisture from the air are often quite effective at reducing condensation.

The most suitable plants for the job include tillandsia, English ivy, Boston ferns, and spider plants. Tillandsia plants in particular don’t require soil and need very little attention, which makes them ideal for bathrooms.

Condensation can lead to the growth of black mould, but it’s certainly not the only cause. Damp issues can arise from plumbing and drainage leaks, and these are often harder to locate and fix. At Aspect, we have specialist tradespeople who can help with all leak and damp investigation work.

Find out how our trace and access techniques can be used to find any source of damp inside properties. We have experts who install energy-efficient windows, and we can also fit air conditioning units and extractor fans. Book a visit from a member of our team or get in touch to learn more about how we can help prevent condensation.