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While condensation and mildew growth can be caused by construction faults, it is usually caused by moisture generated within the house, such as from cooking, showering or lack of ventilation. The average adult releases 1/2 litre of water per day just by breathing, so it is important to keep all rooms well ventilated.

Condensation happens when air becomes so saturated with water it can’t hold any more moisture. When the air comes into contact with a cold surface such as a window, some of the moisture sticks to the colder surface. Condensation can leave water stains and can lead to mildew growth which will help rot set in.

There are two ways to reduce condensation in your home:

• Heating raises the air temperature so it can hold more moisture
• Ventilation allows the moisture to move outside.

Mildew and other fungal growths develop from spores that abound everywhere. Mildew needs moisture to grow, so the more persistently damp an area is, the more likely mildew will grow.

Preventing condensation and mildew

If you have a condensation or mildew problem, try some of these tips. If the problem continues, there may be a construction fault that will need investigation.

• Keep your house warm, generally 5-7°C warmer than outside. A little heat constantly throughout the day is more effective than a lot of heat in the evenings  
• Unflued gas heaters give off moisture as they provide heat, contributing to the moisture burden
• Keep doors to other rooms closed when using the bathroom or kitchen to prevent steam spreading throughout your home
• Clothes driers and extractor fans should be ducted to the outside, not into ceiling or wall cavities
• Use heavy curtains that cover the windows completely so they ‘seal off’ the cooler surface from the warmer air
• Wipe any moisture off glass or other cold surfaces
• Avoid hanging wet clothes indoors to dry
• Limit the number and size of houseplants as they add to the level of moisture in the air  
• Provide ventilation to wardrobes
• Use a dehumidifier in particularly cool and damp areas

Renovating or repairing?

If you are carrying out building repairs or alterations, you should also:

• Insulate the ceiling and wall cavities
• Install the correct building papers on the outside wall frame and under roofing to keep rain and wind out and to absorb moisture if necessary
• Prevent water leaks in walls and roof
• Use dry timber or particleboard. If the materials are wet, allow a drying out spell before finally closing in the structure
• Adequately ventilate the basement or under floor area and insulate with perforated reflective foil
• Repair any faulty drainage so water does not accumulate around the house

Removing mildew

Mildew can usually be washed out of clothing and curtains, but will leave a permanent stain if not done in time.

If you find mildew growing on walls and ceilings, clean the area down with a damp cloth and diluted bleach or white vinegar. Use a test-patch to make sure the bleach does not affect the paint or wallpaper colour. If bleach damages the colour, try undiluted white vinegar or a fungicide solution, which you can buy from most paint or hardware shops. Rinse the area with soap and water and dry thoroughly.

If you are re-wallpapering, strip the old paper off first and paint the wall with a fungicide solution. Allow to dry completely, and rehang wallpaper using a paste containing a fungicide.

If you are repainting, use paint containing a fungicide, but never paint directly over existing mildew.

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