What is Condensation?


Condensation is a relatively new phenomenon resulting mainly from the changes in lifestyle and our desire to keep heating costs as low as possible.


Condensation is related to the way we heat, ventilate and insulate our homes. In days gone by most homes had one or two chimneys which allowed up to four air changes per hour. Doors and windows were generally less well fitting than they are today; this natural ventilation was the very process which prevented condensation.


To cope with increasing fuel costs there has been a trend to insulate by way of loft insulation, cavity wall insulation and double glazing; however, it is a fact that energy efficient homes are more likely to suffer from condensation because anything that keeps warm air in will also keep fresh air out, thus creating the ideal conditions for condensation to form.


Before we can tackle the problem we have to understand exactly what condensation is and then find the best way to deal with it. 

Condensation is merely the air’s natural moisture content settling on cool surfaces. The amount of moisture in the air is called relative humidity. If the humidity level rises about 70%, mould and mildew will be encouraged to grow.


Amazingly the average family creates up to 20 pints of moisture every day simply by washing, cooking and breathing. This moisture must go somewhere and be dealt with to avoid condensation.


What is condensation?

Condensation is water vapour suspended in the air.


Where does most water vapour come from?

The most common sources of water vapour are cooking, drying clothes on radiators, washing up, house plants, moisture in newly built properties and extensions and simply from the breath we exhale.


Where can condensation occur?

Due to the thermal currents within a house, condensation can occur in a number of places, usually at cold spots, i.e, an unheated room or a conservatory without any form of adequate heating.


Condensation forming on the room side surface of a sealed unit indicates high water content present and that the temperature of the room side glass surface is inadequate.


Condensation within the airspace of the sealed unit indicates the unit has broken down.



I did not have condensation before my new windows were installed. There must be something wrong with them.


This s a common assumption but it is incorrect. Windows cannot and will not produce any water. This ‘water’ is produced by our normal living activities, therefore we (the householder) have created the problem.


How do I know if I have condensation?


Condensation will take many forms, the most common being steamed windows and puddles of water on the windowsills. In extreme cases dark spots of mould will appear around the windows, wall coverings and mastic seals throughout the house.


If you have a non-condensing tumble dryer make sure it is properly vented to the outside of your home. Remember, tumble dryers can create 16 pints of water vapour during one cycle.


How can double glazing help?


Sealed unit replacement windows act as an insulator which will reduce heat loss. Under normal circumstances this would be conducted from the inside of the room to the outside. Please remember that sealed units act as an insulator and are not a source of heat, therefore all rooms should be adequately heated, especially conservatories. The likelihood of condensation
forming on a warm surface is therefore reduced.


How do I reduce condensation?

 air brick

Condensation can be controlled by providing natural ventilation to change air on a regular basis and by maintaining an even temperature. This is achieved through ventilating units which are controlled by a humidistat, an airbrick or by opening a window. Please remember that the airbrick must be open to achieve good results. Another effective way of controlling condensation would be to install a dehumidifier, however this cost can be avoided if the problem is one of ventilation, by installing an airbrick and thereby creating ventilation.




Two sleeping adult exude two pints of moisture in eight hours which is absorbed as water vapour into the atmosphere.


New Property


The bricks, timber, concrete and other materials in an average 3-bedroom house absorb 1500 gallons of water. The same principle will apply to a conservatory base and the construction materials used. As with any new building work, please allow a period of drying out to ensure problems are not encountered in the future.


Double Glazing cannot cause Condensation


By acting as a heat barrier and providing an inner pane which is considerably warmer than the outer pane, the likelihood of condensation is reduced.




Condensation is the result of a build up of moisture caused by normal lifestyles and the continual improvement and modernisation of our homes.


Replacement windows cannot produce condensation.
Double glazing will act as an insulator if there is sufficient heat within the house in the beginning. It is therefore wise to attempt to control the amount of water vapour displaced within the household and to provide controlled ventilation to dispel the moisture before a problem arises.              



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