Recommendations for Dealing with Condensation

British Standard 5250: 2002 suggests that information should be given to owners and occupiers of premises on the control of condensation. We have therefore quoted the information in this document.

Why does Condensation occur? Condensation occurs when moist air comes into contact with air, or a surface, which is at a lower temperature.

Sources of condensation – The moisture in the air comes from a number of sources with the property from breathing (while asleep or aware), cooking, washing and drying clothes among others.

In recent times houses have become better insulated and the removal of open fire places and the introduction of central heating have reduced the amount of natural ventilation. These measures help retain the moisture produced within the house and provide better conditions for
condensation to occur. The table below illustrated moisture generation levels within occupied buildings.

Household Activity Moisture Generation Rate
People 0.4 - 0.55 kg/h per person
Cooking 2,000 - 3,000 kg per day
Dishwashing 400g/day
Bathing/Washing 200g/person per day
Washing Clothes 500g/day
Drying Clothes Indoors 1,500g/person per day

It is generally accepted that between 3.5 kg and 16 kg of moisture can be generated into the air each day depending on the number of persons in the household.

a) Keep all rooms warm and ventilated.

b) Keep the internal kitchen door closed and window open when cooking.

c) Keep the bathroom door closed and the window ajar when bathing or showering, or open the window immediately afterwards.

d) Use an electric extractor fan, if installed, when cooking, washing clothes or bathing, particularly when windows show a sign of misting. Keep doors and windows closed when the fan is in operation. Leave the fan on until the mistiness has cleared; this is especially important where extractor fans have been installed so as to counteract prevailing airflows within the dwelling.

e) Do not use paraffin heaters or flueless gas heaters in unventilated rooms, as every litre of paraffin burnt can produce approximately one litre of water.
Provide adequate ventilation where the use of these heaters is unavoidable.

f) Keep heating on at all times in cold weather. (Intermittent heating causes condensation to be deposited as the air and surfaces cool.)

g) Keep the heating on low if your home is unoccupied during the day.

h) If condensation has occurred:

1) as much as possible should be mopped up;

2) the room should be heated;

3) the window should be opened a little;

4) the door should be shut.
Unless such actions are taken, nuisance condensation can become harmful.

i) If condensation occurs in a room which has a heating appliance with a flue, check the heating installation immediately as the condensation might have appeared because the flue has been blocked.


In landlord/tenant situations, agreements should define the respective responsibilities of the parties for the provision of heat to minimize condensation.These include the responsibilities for running and maintenance costs of the plant provided. The occupier should be given sufficient information to enable him to run the system in the manner intended.


There are various sizes of dehumidifiers commercially available that can be used to treat cases of severe condensation. They are very useful for drying out new buildings or buildings where parts of the structure are wet due to burst pipes or flooding. They are not normally suitable as a cure for regularly occurring condensation.


Wardrobes, fitted cupboards and other large items of furniture should not be placed directly against external walls. The resulting pockets of trapped air can lead to serious surface condensation and mould growth, on the wall and furniture. The contents of wardrobes and cupboards can also be affected.

Heating appliances

The problems of using flueless gas or paraffin heaters and the amount of moisture vapour they produce should be pointed out to the building user and discouraged.

Drying clothes

Where possible, the drying of clothes inside should be avoided. If a heated cupboard is not provided or not used, occupants should be advised to restrict clothes drying within a dwelling to a room fitted with an extractor fan. When extraction is not continuous, controls should be provided to enable the extractor fan to be switched on for clothes drying. It is particularly important not to dry clothes in unventilated rooms, especially those kept at low temperatures. It is essential that tumble driers are vented outside or be of the condensing type.

Ceiling airtightness

It is important, from the point of view of energy conservation and to limit the risk of condensation in the loft, that airflow from the house into the loft is minimized. To achieve this, the ceiling should remain well sealed. If the householder installs products which penetrate the ceiling, the same precautions should be taken as above. The loft access trap can be a potential route for water vapour escape into the loft space. It should be kept closed when access is not required.

New buildings

New buildings often take a long time before they are fully dried out. While this is happening, they need extra heat and ventilation; certainly during the first winter of use, many houses and flats require more heat than they will need in subsequent winters. Occupiers should be made aware of the extra care required during these first few months in allowing ventilation for the release of moisture vapour, and the mopping up of condensation before damage occurs to the decoration and fabric of the building.

Curtains and internal blinds

The effect of a curtain or internal blind on a window is to further reduce the window surface temperature and increase condensation on the glass. The use of trickle ventilators can help to alleviate the problem.

Roof ventilation

If roof ventilation is installed, ensure that it is not obstructed by insulation or goods stored in the loft.


© Manchester Residential Managment Limited

Company Number: 5324246