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Tenant Guide to Condensation Damp and Mould

Introduction to Damp and Mould Growth

This guide is designed to give some basic information and advice about one of the most common housing issues, dampness and mould growth. Condensation is usually the biggest cause of damp within homes. Here you will find information and advice to help you identify and reduce condensation as well as treating the mould growth that often comes with it.

Damp can cause mould on walls and furniture and make window frames rot. Damp housing encourages the growth of mould and mites, as mites feed on mould and can increase the risk of respiratory illnesses in some people. Some damp is caused by condensation. This leaflet explains how condensation forms and how you can keep it to a minimum to reduce the risk of damp and mould

Types of Dampness

  • Penetrating Dampness

This type of dampness is usually found on external walls or due to roof leaks on ceilings. It only appears because of a defect outside the home, such as missing pointing, cracked rendering, missing roof tiles or defective rainwater goods. These defects then allow water to pass from the outside to the inner surfaces. Penetrating dampness is far more noticeable following rainfall and will normally appear as a well defined ‘damp-patch’ which looks and feels damp to the touch. Note. Black mould is rarely seen on areas of penetrating dampness. This is because the affected area is usually too wet and the dampness contains salts picked up when passing through the wall, which prevent the growth of black mould.


  • Defective Plumbing

Leaks from water and waste pipes, especially in bathrooms and kitchens, are relatively common. The affected area looks and feels damp to the tough and remains damp whatever the weather conditions outside. A quick examination of the water and waste pipes serving the kitchen and bathroom and the seals around the bath, shower and sinks; plus the external pipework, such as guttering will usually find the source of the problem. Note. Black mould is rarely seen on this type of dampness as the area is usually too wet and the chemicals in a waste water leak will prevent mould growth.


  • Rising Damp

This is generally caused by water rising from the ground into the home. The water gets through or round a broken damp proof course (DPC) or passes through the natural brickwork if the property has no DPC. A DPC is a horizontal layer of waterproof material in the walls of a building just above ground level to stop moisture rising through the walls by capillary action. Rising damp will usually only affect basements and ground floor rooms. It will normally rise no more than 12 to 24 inches above ground level and usually leaves a ‘tide mark’ low on the wall. You may also notice white salts on the affected areas called efflorescence salts. Rising damp will be present all year round but is more noticeable in winter. If left untreated it may cause wall plaster to crumble and paper to lift in the affected area. Note. Black mould will not usually be seen where there is rising damp. This is because rising dampness carries with it ground salts which prevent the growth of black mould. However, secondary factors can result in conditions becoming varied


If property damage is caused by tenants’ poorly managing condensation, then costs for remedial repairs and redecoration will be charged against tenant deposits. Here is some advice on how to avoid these charges, and to make your rental property a more pleasant place to live.

Condensation causes significant damage in our homes to wallpaper, paintwork, and plaster. It can also react with the plaster ‘skim’ coat to cause ‘salting’.

What is condensation?

Condensation occurs when water is released from the air. Air contains varying amounts of water vapour depending on its temperature. Warmer air holds more moisture and when it comes in to contact with colder air or a colder surface, the air cannot hold as much moisture and releases it as condensation. Condensation is most noticeable where it forms on a non-absorbent surface, such as tiles, mirrors, or windows. It can form on any surface however, and it may not be noticeable until mould grows, or the surface starts to rot.

Condensation can occur throughout the year but forms more easily as it gets colder. Growth of mould increases from October to March and during the summer is less common.


Effects of condensation

  • Health risks. Condensation and mould growth are associated with:
    • Mould/fungal growth if left untreated
    •  House dust mites
    • Cardiovascular and respiratory illness
  • Mould spores are released into the air when mould grows. The spores are microscopic, so are easily breathed in and can be potent allergens. They are always in the air and thrive on moisture.
  • House dust mites live in soft furnishings, bedding and carpets. They are invisible to the naked eye and whilst they themselves don’t cause direct harm, their droppings are so small that they are easily breathed in and cause allergies. Warmth and moisture are ideal breeding conditions for them! Exposure to either of these over a prolonged period and at high concentration can cause increased sensitivity. Once sensitised, even low concentrations of these allergens can trigger allergic reactions;, runny nose /sneezing, coughs and wheezing, eye infections, irritation, and eczema to name a few.

Where does the moisture come from?

Moisture in the air comes from many sources of water vapour within the house. It is produced in significant quantities from normal day to day activities.


Black mould growth is the most common effect of condensation, but mould can appear in other colours such as grey or green on carpets, clothing and wood.

Where does condensation occur?

Condensation is made worse by keeping the moist air in the house and can be avoided with adequate ventilation. In certain areas of a house (the bathroom and kitchen especially) the air is warm so contains a lot of moisture. If that air spreads to cooler parts of the house, it will condense on any colder surface. Ventilation is only effective if used consistently throughout the property.

Condensation is made worse by poor air circulation such as behind furniture and in cupboards and the first evidence is often the appearance of mould.

Modern lifestyles mean that many houses are unoccupied and unheated during the day, thus allowing the building to cool down. Moisture producing activities are then concentrated into short periods (morning and evening) when the structure is still relatively cold, and the building is just warming up. A combination of heating and ventilation should be used as the main form of control. A change of air is recommended in all rooms, at least once a day. Most importantly you should limit the amount of moisture in the air.

Signs to watch out for

If your property is too cold:

  • Your house, clothing & bedding will feel cold and damp.
  • There may be a musty, damp smell.
  • You may see mould growth on furniture, external walls, in cupboards, around windows and even on clothing/bedding.
  • Wallpaper may start to peel off.
  • Heating takes longer to take effect, and walls stay cold to the touch.

Controlling condensation


Limit air moisture by:

  • Putting lids on boiling pans, keeping a window open and doors closed when cooking.
  • Air-dry laundry outdoors NOT inside the property.
  • Use a tumble dryer if you have one.
  • If you must dry clothes inside, the airer should be next to an open window and heating should be on.
  • Hanging wet coats in the hallway when people visit.
  • Use moisture traps.
  • Mop up puddles of water on windowsills etc.
  • Keep a window open when ironing.

Maximise ventilation

  • Open a window and close the door, when taking a shower or bathing.
  • Open windows daily for up to 30-60 minutes at a time. Don’t over-ventilate the property.
  • Position furniture slightly away from the walls, so the air can freely flow around the room.
  • Don’t over-fill cupboards - again, let the air flow.
  • Ensure trickle vent flaps on windows are open and air vents are unblocked.
  • Ensure extractor fans in kitchen & bathroom are on and in good working condition.

Heating your home

  • Ensure heating is thermostatically controlled wherever possible to between 18 -21C.
  • Use the timer facility on your boiler to control heating.
  • Keeping heating on low all day in cold weather. (This is more economical than blasting the heating for short periods!).
  • Ensure that heating is turned up for a minimum of 3 hours. Any less will make the problem worse as air will absorb the water vapour more quickly than walls can heat up. Then, when heating is turned off, the air will cool quickly causing rapid condensation and cooling walls further.

To remove mould growth:

If mould growth appears, here’s what to do:
  1. Wash the area with an anti-mould cleaner or non-ammonia soap/detergent, and hot water.
  2. Rinse and dry the affected area.
  3. Use anti-mould disinfectant or diluted bleach after cleaning to ensure that most micro-organisms are killed.
  4. Wash any fabrics/clothing/soft-furnishings in the washing machine on as high a temperature as possible, without damaging the items.

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