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Condensation Problems in Rental Property


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One the major complaints from a tenant is to contact the Landlord or agent and say they  have  "a damp problem". Quite often they have not opened windows or turned extractors on whilst washing or cooking, they live in a property without  a chimney, that has double glazing and no fresh air is getting in.

They dry their clothes over an electric radiator or heater in the living room or bedroom and before long there is water running down the glass on the windows, black mould occurring on walls, corners of ceiling and in built in cupboards. 

Above: Black mould all over curtains and around window frame and wall.

Problems do occur because of the way in which buildings are built today or have been converted, however many people just do not make sure the property is properly ventilated. Up until the middle of the twentieth century, most houses had high natural ventilation. There was not a lot of home insulation and since energy saving methods such as double glazing have been introduced the problem has got worse.

Imagine a standard "Edwardian / Victorian" house, high ceilings, exposed floorboards, plenty of fireplaces and therefore plenty of fresh air coming in. Today there are wall to wall fitted carpets, laminate flooring, wall insulation, dry lined internal walls.

The following notes provide more  information about condensation   

The effect of moisture generation is increased by keeping the moist air in the property and it is possible to avoid condensation by adequate ventilation. Certain parts of the property like the bathrrom and kitchen will have much more warm air that contains a lot of moisture so it spreads to cooler parts of the property.

Next to shrinkage, condensation is the most common problem in houses.  Condensation occurs when warm moist air meets a cold surface.  The water in the air then either settles as water droplets on the surface (as it does on windows for example), or, if the surface is absorbent, it soaks into the surface.  In the latter case condensation is often not noticed unless or until mould appears. 

Mould tends to appear on surfaces where condensation takes place regularly.  Because the external walls of a room are usually the coldest they tend to be most affected by condensation (and as a result of mould) particularly at the corners of the room.  Mould is often found in cupboards, and behind furniture which is pushed close up against a cold wall, this is because there is poor ventilation in cupboards and behind furniture so that any condensation there gets little chance to dry off. Properties have become more effectively sealed, keeping any moisture produced within the property that provides better conditions for condensation.

Left and below: Typical condensation situation where the windows have not been opened.

The moisture can come from cooking, bathing, washing and drying clothes as well as from paraffin heaters and flue-less gas heaters - even breathing produces condensation.  However there are ways of controlling condensation.  One way is to reduce the amount of moisture in the air (the "humidity"), or another is to increase the warmth of the surface of the walls or other areas affected.  Reducing condensation is the best way of controlling mould but it is possible to use fungicidal washes and paints also. 


  • See that your rooms are always warm and properly ventilated.  Too much ventilation in rooms can carry away too much heat and this can cause wall surfaces to get so cold it will actually encourage condensation rather than reduce it.

  • When cooking, keep kitchen door shut and window open.

  • When using a bath or shower or washing clothes, keep the room door shut and the window open. If it is an internal bathroom, make sure the extractor fan is kept switched on.

  • Drying clothes: Tumble driers produce a great deal of moist air and this should, ideally, be ducted directly to the outside of the house.  If condensation is very bad in the house you should consider drying your clothes outside or in a cool area inside. It will take longer, however there will be less moisture. When you dry clothes inside ventilate the room.

  • When anyone comes into the property in wet coats, hang them outside the living area to dry, if you have a porch, use it.
  • If you use a paraffin heater or flue-less gas heater, be sure the window is open a little.  Remember that every gallon of paraffin burnt produces 10 pints of water*

  • (* One gallon of paraffin when burned produces water vapour which turns into water as soon as it touches cold walls and windows.  The amount of water is often rather more than the original amount of paraffin, because of existing moisture in the air.)

  • In cold weather, keep some heating on all the time, i.e. for 24 hours a day.  The warmer a house the less condensation will occur - providing that the level of humidity is controlled too.

  • Consider using a dehumidifier - most large electrical retailers sell these and they are not expensive for a domestic model. They can remove a surprising amount of water from the air, but they do need emptying.
  • Do not fill cupboards to bursting point - particularly if there are clothes in them. Let the air flow into the cupboards.


A property can be made warmer inside by increasing the level of heating or by increasing the insulation.  It must be remembered, however, that if there is not heating at all in the house then improving the ventilation won't make it any warmer. 

Loft insulation is the most cost-effective way of improving the insulation of a house and a grant may be available from the council towards providing it in certain circumstances and if you are on supplementary benefit, family credit or housing benefit and if the house has less than 3mm of loft insulation.

There are other, more expensive, ways of improving the insulation of a house but loft insulation is the one to start with.  The other ways include; cavity wall insulation, double glazing, internal dry lining of walls and external insulated rendering.  A relatively cheap way of providing a little extra insulation to a wall is to put expanded polystyrene behind the wallpaper (you can buy this in rolls).


  • General: - The most important action to take against mould is to try and reduce the condensation in the ways described earlier.  In particular if you have mould behind furniture or in cupboards then move them away from the cold outside walls if possible and put ventilation holes in the top and bottom of cupboards if necessary

  • Cleaning: - Cleaning away mould is best done using an anti-mould solution or wash and there are a number of different brands now on the market.  A little while after using them the surface should be scrubbed clean with a stiff brush.  These washes kill the mould and it's spores and does provide some short term protection against the re-appearance of mould.

  • Paints with mould inhibitors: - Longer term protection against the re-appearance of mould can be gained by redecorating the area affected with a mould inhibiting paint.  A number of firms produce these (e.g. Macphersons, Bio Kil Chemicals, Glixton, Signpost Paints and Liquid Plastics Ltd).

Several companies produce machines called "dehumidifiers".  These machines remove water from the air and produce heat too.  They cost about £1 - £2 per week to run.  They work best in well heated rooms where the humidity is high.  In poorly heated rooms they have little effect.  The machine has to have a large capacity (an extraction rate of 2-4 litres per day is needed).  Some models are ineffective.  In short these machines may be very helpful in some cases, but are not a sure fire cure for condensation.

Left: Condensation like this will often cling to higher area exposing the black mould

N.B. This information should not be relied on for accuracy and is presented here without the responsibility of jml Property Service and the website it is being displayed at. ©jml property Services 09-04  

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