Condensation - frequently asked questions

Got a condensation question? Have a look at the condensation frequently asked questions below and see if you can find your answer. If you are still stuck, give us a call on 0800 65 22 678 and get one of our condensation and damp specialist to talk it through with you.

What is condensation?

Condensation is the process by which water vapour becomes a liquid. The air in our atmosphere contains anywhere from 0 to 4 % water vapour. This water vapour will remain in the air until either so much water vapour is added to the air that it becomes saturated and can no longer hold the water vapour; or the temperature of the air drops low enough that the air can no longer hold the water vapour. In either case the water vapour turns into liquid and forms on a surface as condensation that can eventually develop into condensation black mould. Find out more by watching our condensation video.

What does condensation indicate?

When you see condensation forming on your windows it is a warning that there is too much water vapour in the air of your home or that there is insufficient air circulation next to the windows on which the condensation is occurring. Find out how to reduce the condensation in your home by reading our condensation tips webpage

What causes condensation?

Condensation is caused by the air temperature becoming too low to hold the water vapour that is in it. The factors involved in condensation are as follows:

The amount of water vapour in the air of the home (measured in relative humidity)
The circulation of the air within the home
The air temperature both in the home and outside

The air in a room contains water vapour. The amount of water vapour in the air varies and is commonly expressed in terms of relative humidity. Relative humidity is the measure of the amount of water vapour actually in the air compared to the maximum amount of water vapour the air can hold at that particular temperature and pressure.

Condensation around the window In short: the fundamental principle concerning air and relative humidity is: the warmer the air temperature, the greater its capacity for holding water vapour thus the more likely condensation will occur. When warm air in a room comes in contact with a cold surface, the air around that surface begins to cool. As it cools, the ability for air to hold water vapour decreases. Eventually, it reaches a temperature at which it can no longer hold the water vapour. This is sometimes referred to as the dew point. When the air reaches this point the water vapour begins to condensate, forming as tiny droplets of water on the cooler surface. More often, this is evident within glass in your windows which is also the reason why condensation and black mould often develops there first. Find out more by viewing our condensation video.

Where does water vapour that causes condensation come from?

Water becomes vapour by a process known as evaporation. Evaporation is the opposite of condensation. The air in a home gains water vapour by evaporation from a number of sources. The most obvious sources are running water in sinks, baths and showers, washing machines, and water generated from cooking. Some less obvious sources may include house plants, the ground beneath the house, leaky basements, humid outside air allowed in through open windows or doors, any new construction materials and even the air that you exhale contains water vapour produced by your body. (Find out more regarding the causes to excess water in your property by downloading our handy condensation help guide)

Newly built or remodelled homes will acquire excessive amounts of water vapour from the new materials and finishes used in the project. As the water evaporates from these materials it will cause high levels of relative humidity in the home until the materials stabilize and the humid air is properly vented.

How does air circulation affect condensation?

Air circulation affects the supply of fresh air to the living areas of your home. Poor air circulation within your home will cause the air next to your windows to cool down quickly. When air remains still next to a cool surface, it cools down sooner than air that is well circulated. As the room air temperature decreases, its ability to hold the water vapour decreases thus increasing the potential for condensation to develop.

Drapes, blinds or other coverings tend to trap air next to the window greatly reducing the air circulation around them. Bay and bow windows and other windows that extend from the walls of the home outward are also susceptible to air circulation problems. When possible, try to open these windows and blinds to help improve the air flow within your property. For further information and help, check out our condensation tips webpage.

How does air quality affect condensation?

Not only is it important to have good air circulation in a home to prevent condensation, but the quality of the air that is being circulated is very important. The new home construction designs and materials that are used today help make homes more energy efficient and air-tight. This has also unfortunately, greatly affected the quality of the air in the home and also caused condensation related enquiries to become more frequent. Most heating and cooling systems are used as the primary air circulation system. In a modern air-tight home, these systems will only circulate the air already within the home unless a fresh air supply system is also used. Fresh air supply is mandatory to properly vent and maintain humidity levels in the home, preventing musty smells, condensation and mould growth.

How does the temperature affect condensation?

Condensation cold spots The amount of water vapour air can hold is directly related to the air temperature and the amount of condensation produced. Warmer air can hold more water vapour than cooler air. When warm air is cooled it loses its capacity to hold water vapour and, if it cools enough, it will begin to condensate and produce condensation and mould growth.

During the summer, the air temperature in your home will probably be maintained at a fairly constant temperature. The real affect of temperature and its impact on condensation will be the relationship between the indoor air temperature and the outside temperature during the winter. The colder the temperature outside the colder the glass surface temperature will become as well as the air temperature in the hidden structural areas of your home. As these areas cool down the air near them begins to cool as well. The air temperature in the room may be relatively unaffected, but the air next to the window glass or in these hidden areas will cool down. The air in these areas may cool below its maximum vapour saturation point and condensation will begin to form.

What happens if I ignore the Condensation?

Condensatiuon Affects health Common sense tells you not to! If not rectified, condensation will cause significant damage to your home and belongings. Unsightly stains, mould and mildew are only the visual signs but these can lead to costly redecorating. It can also be the cause of poor health and respiratory problems. Condensation is one of the symptoms of too much moisture in the home. Controlling condensation is the best investment you could make in your home and your families health. Find out more by downloading our condensation help pack.

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