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Condensation occurs when water vapour in the air changes back to its original liquid state - water.

Outside, condensation may appear as clouds, fog, mist, dew or frost. Inside it will appear as ‘steam’ in the air, liquid condensation on windows and cold surfaces or damp on walls and ceilings. It will also result in damp bedding, drapes, carpets, clothes, etc. For example, a fabric lounge suite can hold up to 4 litres of moisture and a queen sized bed up to 10 litres.

Condensation is the result of 2 different air temperatures meeting each other. All air contains varying quantities of moisture in the form of water vapour. The cooler the air, the less water vapour, the warmer the air the more water vapour. That is why the North and South Poles are actually very dry and experience very little rain while the equatorial areas are hot and have high humidity - and experience lots of rain.

When warm air is cooled, relative humidity increases, until at a particular temperature, called the dew point, the air becomes saturated. Further cooling below the dew point will induce condensation of the excess water vapour. This process is observed outside by the formation of clouds which occur when warm moist air rises. Eventually the clouds rise high enough to cool or meet cool air currents that reduce the air temperature resulting in the water vapour turning back into water and falling to earth as rain. The same thing occurs in your bathroom shower.

Warm moist air rises in the shower cubicle until it meets the relatively cooler air in the bathroom. Where these two air masses meet, visible water vapour occurs – that’s the clouds of ‘steam’ you see. (It’s incorrectly called steam because real steam only occurs when the temperature in over 100 degrees centigrade – that would scald.)

CONDENSATION IN THE HOME

Condensation problems in buildings and particularly homes arise because air can hold only a limited amount of water vapour, and that amount varies with temperature. Occupants are constantly adding warm moist air into the building from cooking, breathing, heating, washing dishes and clothes, showering, etc.

It’s believed an average family of 4 releases around 10 litres of water into the home every day. Up to 1 litre can be released from a single 10 minute shower in some conditions. By reducing the amount of moist air expelled into the home the problems associated with condensation will be reduced.

More condensation problems occur in homes during winter because the house is more likely to be kept closed up to retain warmth. The variation in inside and outside temperatures is also greater. This is why you will notice a ‘steamy’ bathroom in winter but not in summer. The difference between the water temperature in the shower and the temperature in the bathroom is likely to be greater in winter – therefore more visible moisture or water vapour is formed.

Condensation usually occurs first on windows and mirrors because they have the lowest temperature of any of the interior surfaces in the house. It can also occur on ceilings and on the exterior walls particularly on the cold side of homes where there is either insufficient or no insulation.

Mould and mildew growth is fairly common on the colder side of most homes where the indoor moisture levels are too high.

The best way of controlling moisture in homes is through ventilation. Dehumidifying the home by ventilation works simply by replacing warm wet air inside the home with drier air from outside. This is often not possible or particularly desirable when the exterior weather conditions are moist or cold. Excellent home ventilation systems are available which work on the principle of improving ventilation through the use of warm dry air in the roof cavity. Most of these are excellent systems and do make homes healthier and more comfortable to live in.

A simpler and more economical method is to reduce the amount of warm moist air being created in the home. Be sure to expel all cooking moisture through a range hood, ventilate laundry driers to the outside and do not use unflued gas heaters. Stopping the moisture in the bathroom is the easiest and cheapest of all and it eradicates the greatest moisture creation in the house – fit a Showerdome.

It simply creates a barrier between the warm rising moist air in the shower cubicle and the cooler air mass in the bathroom. No steam is made.