The causes of condensation at home and how to reduce it

When water droplets form naturally on the inside of your windows or walls, this is condensation. Signs that you have significant condensation problems in your house include streaming windows, peeling wallpaper, mould growth and a musty smell. To ensure your property and health doesn’t suffer adverse effects, reduce condensation wherever possible.

reduce condensation

What is condensation and how is it linked to humidity levels?

Condensation is formed when warm, moist air cools quickly. For example, when it comes into contact with a colder surface. The warmer the air, the more water vapour it can hold. Air at 30C can hold more water vapour than air at 20C. 

When air at a constant temperature can’t hold any more water vapour, the humidity is 100%. If the air temperature drops, it can no longer hold that water vapour – it condenses and water droplets are created. This is condensation. Warm air meeting a cold surface causes the air temperature to drop and condensation occurs.

What causes condensation in my house?

Once you’ve noticed it in your property, the next step is to identify what causes condensation. Any activity that uses water which is allowed to evaporate will add water vapour to the air and increase humidity:

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

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 some usually ends up as condensation on walls or surfaces around the house.

Why is condensation worse in the winter than in the summer?

At the end of autumn and beginning of winter when the outside temperature drops, condensation is more likely to appear. This is because colder windows and walls will cool the warm, moist air indoors faster.

However, two homes heated to 24C and both with 60% humidity may experience very different levels of condensation. In a home with very efficient glazing and insulation, condensation might not form. 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 “comfort temperature” that we feel most comfortable in. This is usually the temperature that most central heating systems are set to. 

How can I prevent condensation from forming in my house? 

Reducing activity that creates water vapour and increases humidity in your home would help to reduce condensation levels. However, this isn’t always practical or possible. A couple of the most effective ways of reducing condensation are ones you can do straight away. 

First, expel moist air before it circulates throughout the home. Secondly, allow humid internal air to exchange with drier external air. Other long term solutions will involve some home maintenance which we will cover later on.

Air extractor units

Extractor fans expel humid air before it circulates. These should be installed in bathrooms and kitchens. Keeping the doors of these rooms closed will help to keep humidity levels lower in other rooms. Doors can be opened again once the humid air has been expelled or exchanged.  

Check your air extractors are working correctly and that they’re always turned on whenever water vapour is being created. Ideally, leave them running for 5 minutes after, too.

A properly functioning cooker hood that vents externally is needed rather than a recycling one. Recycling kitchen extractors will remove smells and particles but won’t remove water vapour from the air.  

Consider upgrading your bathroom extractor so that it turns on automatically and continues to run for a short time after.

Improve ventilation with air exchange

Ventilating a room with outdoor air helps to reduce humidity. This in turn reduces the chances of condensation forming. This works as air from outside with a lower humidity level replaces the warm, humid air that’s indoors.

Some research shows that humidity can be beneficial to health, so long as the air isn’t over moisturised. The moisture is good for your skin and also lets you breathe easier than in really dry air. As with many things, there is a happy medium for humidity, and this is seen as being between 40-60%. A hygrometer measures humidity levels.

Open windows

The easiest solution is to open a window in rooms that suffer from condensation. Keeping internal doors open allows humidity levels to increase throughout the home. Keep doors closed just as you would with an air extractor on.

Opening a window for just a few minutes may be enough to reduce humidity levels enough to prevent condensation from forming. 

Open trickle vents

Trickle vents are small vents built into windows that help with ventilation. They allow indoor and outdoor air to exchange constantly. 

It can sometimes be tempting to close trickle vents to reduce draughts, particularly in winter. We’ve seen some people blocking them by taping over the vent when cold air is coming through. This isn’t a draught caused by faulty insulation, but a deliberate ventilation feature.

If you don’t have trickle vents, you can retro-fit them into most window frames, uPVC or wooden. However, it requires specialist knowledge and skill to do so.

Renovated properties
Victorian era houses were generally built with relatively thin, single skinned walls and single glazed windows. These features mean they aren’t as well insulated as modern houses. Chimney breasts and air bricks helped with ventilation.

When houses are refurbished it’s common for chimney breasts to be removed and for air bricks to be blocked. This is poor practice as condensation problems are likely to occur unless alternative ventilation is added.

Dry clothes outside

When drying laundry, try to dry it outside where possible. If this isn’t an option, keep windows open near the drying clothes to help the moisture escape. If you have a tumble dryer, make sure it vents externally and is not filling your home with warm, humid air. 

When drying clothes inside, open a window and close the door to other rooms.

Extra spin cycles
Most modern washing machines have an option for a spin only cycle. This will usually remove more water by spinning the load at a high speed without adding more water.

Drying clothes on radiators means your central heating system will have to work harder. This is because the clothes are acting as a barrier against effective heat transfer into the room. 

Why you should reduce condensation if it’s produced in your home 

Drops of condensation can evaporate as water vapour if the humidity level is low enough. However, most of the time it will begin to trickle off the windows and walls.

Water running off windows and walls can seep into porous materials such as wooden window sills and skirting boards. This water damage can cause paint to crack and peel. Eventually the damp conditions will soften wood and eventually cause it to rot.

Where the condensation has seeped into walls and around windows you may also start to see signs of damp. As well as being unsightly, damp can produce an unpleasant, musty smell. When left untreated, it can also become a prime spot for mould and mildew to form, which can damage your health. They like dark and still conditions, but consistent damp will allow them to grow in light areas too. 

Home improvements to reduce condensation

To reduce condensation, you have to reduce the excess moisture in the air. There are many simple ways to do this. The key is to improve ventilation and insulation. For long term solutions, you might need to invest in some home improvements.

Check that your windows are energy efficient

Single glazed windows are very susceptible to condensation, particularly in the winter. This is because there is only one pane of glass which is kept cool by the outdoor temperature. However, double or triple glazed windows are much more energy efficient. 

The space sealed  between the panes of glass is either filled with gas, or is a vacuum. This space reduces heat transfer, so the outer pane keeps cool while the inner pane keeps close to the temperature indoors. 

Condensation inside multi-glazed windows
If you have condensation between multi-glazed window panes it means the gas inside has escaped. Air has got in, probably via a damaged seal. The only way to resolve this is to replace the unit.

Efficient cavity wall insulation

Condensation can occur on a cool surface. It’s usually seen on windows but can form on the walls of a property too. Without proper insulation, the cold outdoor temperature will seep through and make the internal walls of a property cold too. Then when the warm, humid air comes into contact with the now-cool wall, the water vapour turns into condensation. 

The empty space between the outer and inner walls goes some way to insulating a property. However, it’s far more efficient if the cavity is filled with insulation. Insulating cavity walls stops cold outdoors temperatures from cooling the inner wall. 

Homes built in the 1920s and onwards are likely to have been built with cavity walls. Those built within the last 20 years probably already have cavity wall insulation. 

Is a dehumidifier the best way to reduce condensation?

These appliances draw in the humid air from a room and release it as drier air. For rooms that constantly suffer from condensation, damp, and high humidity, they are very effective. However, they’re not the best long-term solution to condensation problems as they use a lot of energy. 

Will an air conditioner reduce condensation?

A/C units work by sucking in warm air and cooling it. When the warm, humid air passes through the unit, the water vapour condenses onto an evaporating coil and then drains away. 

An air conditioner will reduce condensation, but won’t be the most cost effective solution.

When you get into a car on a cold day the moisture from your warm breath condenses on the cold windows. The air conditioner removes moisture from the air as it cools it. The temperature difference between the cold windows and air is reduced. 

Does anti-condensation paint work?

Some specially designed paints can prevent the build-up of condensation on walls. The paint essentially acts like an additional insulating layer. Depending on the wall and the insulation behind it, the extent to which this paint works would be limited.

Fun tip! Decorate with houseplants

While obviously not a solo solution, some common houseplants can help reduce humidity when used in addition to other methods. Plants that thrive in humid environments and draw the moisture from the air can prove effective in helping to reduce condensation. 

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

Condensation can be a cause for mould growth. However, it’s certainly not the only cause. Damp issues caused either by water ingress, or by plumbing or drainage leaks, can be harder to locate and fix. We have specialist tradespeople who can help with all leak and damp investigation work.

Read how our use of trace and access techniques are used to find any source of damp problem.


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