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Condensation, Damp and Mould


Problems of condensation leading to damp and mould growth are a common problem.

This page sets out to explain how condensation occurs and how it leads to mould growth if the problem gets out of control.

Sometimes, tenants believe that the problem is caused by a defect that affects their home and the solution to these issues lies with their landlord; however, this is not always the case. It is vitally important that the occupiers carry out some basic steps to ensure that they reduce the likelihood of a problem occurring.

At the end of the page we explain what help is available if you believe that despite following our advice, there are problems that your landlord ought to be dealing with.

What is condensation?

Condensation is caused when moisture held in warmer air meets a cold surface like a window or wall and condenses into water droplets. If this happens regularly, mould may start to grow. This usually appears on cold outside walls and surfaces and in areas where the air does not circulate well.

Why do you get condensation?

The air we breathe can hold varying amounts of water vapour, depending on its temperature. If warm moist air is cooled by a cold surface, such as a window or external wall, it is then no longer able to hold the same amount of water vapour.

Think about how your warm breath appears as a cloud of vapour when you breathe outside on a cold night.

The airborne moisture turns into droplets of water and collects on the cold surface. This is called condensation.

Why is mould appearing?

Microscopic mould spores are always naturally present in our atmosphere both inside and outside our homes. Its only when there is a suitable atmosphere, such as arises when excessive condensation or high levels of humidity are present, that moulds become evident as they group together to form black or green spots on walls, on the back of cupboards, inside wardrobes or on furniture, soft furnishing or clothes etc.

When is it a problem?

Every home gets condensation at some time - usually when lots of moisture and steam are being produced - for example, at bath times, when a main meal is being cooked or when clothes are being washed. It is quite normal to find your bedroom windows misted up in the morning after a cold night.

How Much moisture can be produced in your home in a day?

Two people active for one day3 Pints
Cooking and boiling a kettle6 pints
Having a bath or shower2 pints
Washing clothes1 pint
Drying clothes9 pints
Using a paraffin or bottled gas heater3 pints
Total amount of moisture produced in your home in one day24 pints

Are you sure it is condensation?

Condensation is surface dampness.

It mainly occurs on cold walls indoors, particularly in corners or behind furniture where the air is static, and other cold surfaces such as tiles, around window openings, and cold water supply pipes and under sinks and basins.

Condensation is usually at its worst during the winter. It often results in black mould growing on walls and other surfaces.

What is the difference between Dampness and Condensation?

Dampness occurs when a fault in the basic structure of the building lets in water from the outside. There are basically two types of damp:

  • Penetrating damp Penetrating damp occurs if water is coming in through the walls or roof, for example, under a loose roof tile or through cracks on the outside wall of the house. The usual signs are pale brown or straw coloured staining, a musty smell and wet patches on the walls or ceilings after rain. 
  • Rising damp Rising damp occurs if there is a problem with the damp proof course which is a barrier that is built into floors and walls to stop moisture rising through the house from the ground. The usual evidence of rising damp is a 'tide mark' on the walls which shows how high the dampness has risen. There can also be a musty smell. It is prudent to carry out a Calcium Carbide Test (often known as a 'Speedy test') to confirm rising damp is the definite cause, as it is possible for high levels of condensation to form at the base of walls, giving the appearance of rising damp.

What about leaking pipes or unsealed showers and baths?

Water leaks from pipes or escaping through the tiling seal between bath or shower trays eventually evaporates and adds to airborne moisture within your home, potentially making condensation worse.

If you have any Rising or Penetrating Dampness, or there are Water Leaks, notify your Landlord/Agent/Owner immediately.

The four main ways to deal with condensation are:

  • Produce less water vapour or steam in your home;
  • Don't let the water vapour and steam that is produced spread all round the house.
  • Keep your home ventilated, but don't over ventilate.
  • Keep your home warm.

To deal with a condensation problem effectively you will need to do all four.

1. Produce less water vapour.

The amount of condensation depends on how much water vapour is in the air. Many everyday activities add to the water vapour level in your home, but their effect can be kept to a minimum.


Cover pans when you are cooking. Don't leave kettles and pans boiling longer than necessary. Use the cooker hood extractor if you have one, as long as it's the type that takes fumes and steam to the outside. If there is a fan in the kitchen, always use it.

Drying clothes:

Hang washing outside to dry whenever you can. If you have a tumble dryer make sure it is vented to the outside, unless it is a condenser-type dryer.

Follow the manufacturer's instructions regarding room ventilation, even if you have a condenser type dryer - these still need correct room ventilation to work effectively.

This is very important; one of the common causes of mould growth in homes results from using tumble dryers without venting them correctly.

The hot moisture-laden air will migrate to the cooler areas elsewhere in your home - perhaps far away from the tumble dryer in upstairs rooms - and cause condensation and mould to appear on clothes, window blind slats and window frames etc.

If you have a condenser dryer, please read the instructions which will tell you how much ventilation your dryer needs to work properly and therefore not add to condensation/mould problems within your home. As a bonus, your condenser dryer will cost less to run if it has suitable ventilation, as it will work more effectively.

If you must dry clothes indoors, restrict this to the bathroom and keep the door closed/window open. Don't cover radiators with drying clothes.


Run the cold water into the bath first, to minimise steam production. Keep the bathroom door shut and the room well heated and ventilated.

This applies even after you have finished using the bath or shower, so that the moisture laden air is fully removed. Use the fan if one is fitted, and leave it running after you have finished until the moist air has gone.

Paraffin and some types of gas heaters:

  • Avoid using these type of heaters - they are one of the main causes of major condensation problems
  • One litre of water is produced by one litre of gas or paraffin burning. Paraffin heaters, portable bottled gas heaters and fixed flue less gas heaters all produce heat but at the same time they also put a lot of water vapour into the air. Paraffin and bottled gas heater can also be dangerous and expensive to run. They can cost as much as, or even more than, heating using peak rate electricity.

2. Don't let it spread

Confine wet air to just a few rooms.

  • Your bathroom and kitchen are 'wet rooms' - keep these doors shut so that the wet air can't spread to the rest of the home
  • Especially when you are washing, cooking or taking a shower or bath, keep the doors shut
  • At the same time make sure your bathroom or kitchen are well ventilated so the water can escape outside
  • This is even more important if some rooms are very cold

3. Keep your home ventilated

Let wet air out

The best way to remove water vapour is by providing adequate ventilation. Nobody likes drafts, but some ventilation is vital.

  • Keep a small window ajar or trickle ventilator open, in each occupied room, but make sure your home is still secure. Many types of modern windows have a lockable 'night vent' position built in to the latch mechanism
  • Open the windows enough to let the water vapour out, especially when you are doing the washing or cooking
  • Windows near the ceiling are more effective at letting the water vapour out than ones lower down
  • Don't over-do it; if you leave windows open wide for too long the rooms will become cold and actually make condensation more likely as the surfaces will be cold

4. Keep your home warm

Heating your home can help solve a condensation problem, but only if it's used in addition to the other three steps already described. However, first of all it needs to be dry heat, such as central heating or gas fires. Not paraffin or portable heaters.

Secondly, simply heating your home will tend to warm the air. Warmer air holds more water vapour, so this means there will be more water to condense out onto cold surfaces.

This is more likely to be a problem if you only put the heating on for an hour in the morning and an hour at night. In this case the air is warmed, and the room surfaces stay cold, so there is more chance of warm moist air being in contact with cold surfaces.

The best approach to heating in order to reduce condensation, assuming you have taken the other three steps, is to heat your home at a low level for a long time.

Keep the heating on, but set it to provide the minimum of background heating. This will warm the whole building and keep it warm, so there are no cold surfaces.

Don't block radiators or heaters with clothes, furniture or beds. Ensure that there is plenty of room around any thermostatic radiator valve so it can work properly.

Dealing with mould growth

The best way of tackling mould growth is to reduce condensation levels and prevent it from growing in the first place.

Dampness from condensation often causes the growth of black mould on walls and other cold surfaces such as tiles.

Mould and mildew can also grow on furnishings, curtains and even clothes in wardrobes. It may first appear in corners or behind wardrobes, but it can spread across entire walls.

Mould on washable surfaces is best dealt with by wiping down with a proprietary mould treatment or a weak bleach solution. It can be washed out of fabrics, but may leave stains and spoil colours.

What else can I do?

Install a humidistat extractor fan

Humidistat fans should be sited in kitchens and bathrooms and will automatically operate at a preset humidity level to assist with the required air changes. They help to remove the moisture at source and are useful where cross ventilation via open windows or trickle ventilation has not fully eradicated the problem.

Some bathrooms and kitchens are fitted with a type of modern fan that is designed to be left permanently switched on. These fans have sensors that detect moisture in the air and run the fan continuously at low speed, or fast speed if there is a lot of moisture present. These fans use very little electricity; their running costs are fully offset by the savings made by not having lots of condensation problems and damp.

What about dehumidifiers?

De-humidifiers may cost approximately £200-£300 to buy and must be emptied every day. They are useful for drying damp buildings out, for example after leak damage, or for specific rooms.

Dehumidifiers are no substitute for the vital, no-cost measures of reducing the amount of water vapour put into the air and keeping rooms well ventilated and heated.

The human factors

If your home is overcrowded, it is more likely that you will suffer from excessive condensation and this can lead to mould. If you live in a House in Multiple Occupation and there are lots of adults using the bathroom and kitchen, it's vital that the steps outlined above are followed by all occupiers.

Take care when you or your children are using the bath or shower that water stays within the tub or tray. Make sure that any shower curtain works as designed to keep water inside the shower.

My cellar or basement is continually damp and mouldy?

Cellars and basements are not considered habitable parts of the home, and are often damp. It is not expected that these parts of your home will be completely free from damp, although you should advise your landlord straight away if there is standing water in the cellar, or rainwater is regularly entering the cellar during periods of rain.

Cellars are normally ventilated and rely on natural flow of air in order to dry out. If mould appears, ventilation should be checked and any mould treated using a suitable spray.

I am doing all these things but I am still having mould issues or excessive condensation?

In the first instance, if you think there is something wrong with your rented property, please get in touch with your landlord and explain the issues. We always recommend putting your concerns in writing - keep a copy of the letter, email or text for future reference.

Your landlord may be able to help by making some improvements. These can include;

  • Installing extractor fans in bathrooms or kitchens, where a problem is occurring.
  • Installing vents in rooms where there is a lack of appropriate ventilation. This kind of work must be fully considered beforehand, as excessive ventilation or placing it in the wrong place may worsen the problem
  • Improving the insulation levels of the roof and walls, especially in older properties with solid walls
  • Improving or repairing the windows and doors, especially if they are old single-glazing type windows (although in conservation areas, it may not be possible to upgrade to modern double glazing). Other solutions, such as secondary internal glazing may be suitable.
  • Ensuring that a suitable temperature can be maintained by making sure that heating works as designed, and is suitably placed. Radiators should be ideally placed in order to combat cold walls or cold parts of the room - that's why they are traditionally placed below windows. Every habitable room ought to have some kind of fixed heating system, whether it's a radiator or some other type of fixed heater.
  • Ensure that broken heating systems are promptly fixed; if a lack of home heating persists for weeks during cold weather, condensation and mould is highly likely. Your landlord should provide some temporary heating at times when the heating is not working.
  • In properties where problems persist, the landlord may consider engaging a specialist adviser who can suggest alternative solutions. Commonly, this involves installing a Positive Pressure Ventilation Unit - these often work by pulling in dry filtered air, normally from the loft space and uses a low-noise fan to force the dried air throughout the property, thus reducing condensation which in turn, defeats mould growth.

My landlord has told me that the condensation and mould is my fault, and refuses to help?

Make sure you have told your landlord in writing about the problem.

If problems persist, and your landlord refuses to act, please contact the Council.

Please fill out this online form to report a housing standards issue with a property in the Preston area.

Report a housing standards issue

It helps if you can show the Council any letters or emails you have sent to your landlord about this problem.

Depending on your complaint, the Council may visit your home and also speak to your landlord.

We may take informal or formal action towards your landlord to resolve any significant hazards. If the problems of mould growth within your home have reached hazardous levels, the Council expects a landlord to deal with matters regardless of how they have arisen.

This is a duty placed on the Council by the - Housing Act 2004.

A landlord may seek to recover costs for dealing with damage caused by mould growth, from their tenant, if they consider that the problem has arisen due to the tenant failing to adequately maintain a suitable level of humidity within the house.

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