Preventing condensation and mould

Condensation

If you wear glasses you will know what happens when you come into a warm house from the cold outside. The same effect can be seen on a bathroom mirror when you have a hot bath - warm moisture-laden air chills and condenses on contact with the cold surface.

In all, the average family can produce up to 20 litres of water per day, just by their normal day to day activities. Try putting 20 litres into a bucket and seeing how much water you could be putting into your house - day, after day, after day!

There is always some moisture in the air, even if you cannot see it. If the air gets colder, it cannot hold all of the moisture and tiny drops of water appear.

Anywhere where this warm moist air comes into contact with a cold surface is called condensation. This process can occur anywhere in the home.

Condensation is caused by:

Too much moisture in the air
Too little heat
Too little ventilation

Too much condensation leads to mould.

Our work to make homes better insulated

Better cavity wall insulation and improved double glazing, has made your home better insulated and more wind and weather tight. It has also made it warmer, which helps to hold the moisture in the air, rather than condensing on cold surfaces.

But, as you no longer have those draughty windows and doors, the moisture can not be released from your home so easily, so you need to ensure you have adequate ventilation in your home.

Where are you most likely to find condensation?

Condensation often appears in the coldest part of the room or where there is little air movement, and therefore more moisture in the air, such as in corners, on or near windows, or around cupboards and wardrobes.

Cold corners of rooms
Wardrobes
Cupboards, particularly built-in cupboards
Behind furniture against an outside wall.
Cold surfaces such as mirrors, single-glazed windows and metal-framed windows
Kitchens and bathrooms (where moist air is produced through washing, cooking, etc).
Walls of unheated rooms

Why does water appear on my windows/cupboards/walls?

It is a basic law of physics that if the surface is cold enough and if there is enough water vapour in the air then it will condense. Warm moisture will seek out the coldest spots in a room, appearing as condensation.

Mould caused by condensation (different to other forms of damp)

Mould caused by condensation often appears as black spots. Other causes of mould often leave a tide mark.

Condensation is different to surfaces inside the home getting wet from water getting into the house from outside, usually through windows, doors or roofs. This can be dealt with by repairing a defect in the roof, doors or windows.

Rising damp (ie. water coming into the house from the ground) occurs if there is a problem with the damp proof course (the barrier built in floors and walls). The usual evidence for this is a 'tidemark' on the walls. There can also be a musty smell.

Condensation is not always obvious. A wall or floor may not visibly have droplets of water, but may feel damp to the touch.

Can you have mould without condensation?

Too much moisture leads to mould. However, mould occurs around 68% humidity, condensation occurs at 100%. As you can see from this you can have mould but still have clear windows or walls.

Higher heating bills?

Condensation, like all other forms of dampness, makes houses difficult to keep warm. The reason being wet building materials lose heat more quickly than dry ones and also some of the heat input is being used to dry out the house.

Where does this water come from?

We all produce water by drying clothes indoors, poor heating, calor gas heating, the boiling of vegetables, showering, rain, calor gas heating and making cups of tea all produces moisture. It is just an on-going process that never stops.

Reducing moisture

When cooking, cover pans with lids and keep the kitchen door closed
Make sure a window is open or the extractor fan is on
Make sure your tumble dryer is vented to the outside
If you have to dry clothes indoors, put them in the bathroom with the
door closed and the window open or fan on. Or, put them on a clothes
dryer in another room but make sure the door to the room is closed and
the windows are open
When bathing, run cold water into the bath first, then run the hot water. This will minimise steam production.

The average family can produce up to 20 litres of water per day, just by their normal day to day activities.

Ventilation

The most important thing to prevent condensation forming on walls and windows is to prevent water from getting into the air in the first place. After this, the next best thing is to make sure any water in the air can quickly escape from your home.

Too much ventilation (as draughts) can make condensation worse by making homes harder to heat (causing cold surfaces on which condensation forms). But if you seal off all the draughts, then the moist air cannot escape from your home.

It is important to allow plenty of fresh air into your home as otherwise the indoor air will become stale and humid, leading to unhealthy conditions

Always keep a small window ajar or a vent open when someone is in the room. It is best to keep vents open all the time
After you have had a bath or shower you need to open the bathroom window for a while until the steam has cleared, or alternatively use the extractor fan if you have one
When cooking make sure that the kitchen door is closed and either the extractor fan is on (if you have one), or a window is open
Do not switch off or tamper with any ventilation equipment provided in your home
Extractor fans are used to quickly remove damp air from the kitchen and bathroom where the most moisture is produced
Fans should be used whenever you are cooking or bathing
After you have finished in the bathroom or the kitchen leave the fan on for about 20 minutes to ensure that all damp air is cleared
An extractor fan will only work if the windows in the room are kept closed. If a window is open the fan will draw air in from outside, rather than drawing out the damp air from the room
Some fans switch on and off automatically according to the amount of moisture in the air. Do not turn these off at the power switch as they are designed to work when they are needed. If you suspect that they are coming on more or less often than they should, then you need to report this to us.

Your windows may not be the coldest spot in the room (especially if they are double glazed). Condensation may therefore appear on walls, floors and ceilings, even if your window are not steamed up.

Heating your home

It is best to tackle condensation first by reducing moisture in the air, and helping water in the air to escape from your home. However, you can also help prevent condensation by heating your home better.

Heat all rooms even if they are not being used
Do not place furniture or belongings in front of radiators as this will stop them heating the room efficiently
Do not use portable LPG (Calor Gas) heaters. These can produce three pints of moisture in five hours and are prohibited in our homes for health and safety reasons
Do not use the heating on a high setting for short periods of time.
Heating your home for a longer time at a lower temperature will keep your home warmer and cost you less
If you have central heating use the thermostat to control the heating by setting the temperature to a comfortable level. The recommended temperature is 18 degrees C in your hall and 21oC in your living room (or up to 23oC if you have young children or are a pensioner)
If your radiators have thermostatic radiator valves (TRVs), these will give you greater control over the heat from each individual radiator.

Tackling mould once you have it

You may already have a small amount of mould in your home - if you do, there is often no need to call out one of our plumbers to fix the problem. It's often easy to remove with just a bucket of soapy water and a bit of scrubbing.

Other tips include:

Removing small patches of mould that may appear on surfaces using one of the mould cleaning products suitable for that purpose. These are obtainable from supermarkets. Make sure that you use a product which carries a Health and Safety Executive 'approval number', and that you follow the manufacturer's instructions.
Wipe down the inside of windows if they become wet with condensation
Try not to place beds and wardrobes against outside walls as mould is more likely to grow behind furniture.
Don't put too many things in wardrobes and cupboards as it stops the air circulating.
When redecorating bathrooms and kitchens use a paint formulated for these areas.
Do not decorate over walls or ceilings that have been decorated using fungicidal paint, with ordinary paints or wallpapers.
Report any repairs to us. This includes defects to extractor fans and heating systems.

Remember - both us and you, the tenant, are responsible for keeping condensation under control.

Last update: 24/06/2011