Condensation and Mildew

Condensation and mildew in homes can occur all year round if given the right conditions but are especially problematic during winter months. Our Environmental Health team is regularly asked for advice on controlling condensation and mildew in the home. 

Condensation occurs when the air becomes saturated with water vapour to the point where it cannot hold any further moisture. In areas where there is a difference in temperature between two surfaces, such as with windows, some of the moisture will condense on to the colder surface. Condensation can leave water stains and, if persistent, can lead to mildew growth and rot can set in.

Mildew and other fungal growths grow from spores found in the air. Mildew needs moisture in order to grow so the more persistently damp a situation, the more likely mildew will grow.

How can you reduce condensation? There are two ways to reduce the level of condensation in your home - by heating and by ventilating. Heating will raise the air temperature and allow the air to hold more moisture, while ventilation removes the moisture to the outside.

Try this helpful tips to keep condensation and mildew at by:

• Keep the house warm, generally 5-7 degrees warmer than the outside. A little heat constantly throughout the day is more effective than a lot of heat in the evenings.
• Space heaters, open fires or electric heaters are best to provide warmth. Gas or oil heaters give off moisture as they provide heat, thereby contributing to the air moisture burden.
• It is better to have many windows slightly open for long periods than a few wide open for short bursts, as this prevents the home from losing too much heat but also provides a constant level of ventilation. There are times when opening windows wide helps to remove large quantities of moisture rapidly, such as during cooking or when showering or bathing.
• Keep doors closed when using the bathroom or kitchen to prevent the steam spreading throughout your home. Extractor fans over a shower or stove will assist to remove air moisture from the room but do ensure it is ducted outside, not into the ceiling or wall cavities. If you have a clothes drier, ensure it is also ducted to the outside.
• 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 cold surfaces when condensation has occurred.
• Avoid hanging wet clothes indoors to dry out.
• Limit the number and size of houseplants as the plants themselves, along with watering, can add to the level of moisture in the air.
• Provide ventilation to wardrobes by such means as louver doors or cupboard heaters. Products like Damprid remove moisture from the air but they must be changed regularly.
• Dehumidifiers can be helpful, particularly cold and damp areas.

If carrying out building repairs or alterations to your home or business, you should also:

• insulate the ceiling and wall cavities to keep these surfaces warm, thereby lowering the risk of condensation forming.
• install the correct building papers on the outside wall frame and under roofing to keep the rain and wind out and to absorb moisture if necessary.
• look for and address any water leaks in the walls and roof.
• avoid using wet timber or particle board during construction. If the materials are wet, allow them to dry out before finally closing in the structure.
• adequately ventilate the basement or underfloor area and insulate with perforated reflective foil,
• repair any faulty drainage so water does not lie around the house.

Mildew can usually be washed out of clothing and curtains; however, if this is not done in time, it can leave permanent stains.

For mildew growing on walls and ceilings, clean the area with a damp cloth and household bleach: one part bleach to four parts wate. Use a test patch to make sure the bleach does not affect the paint or wallpaper colour. If the colour is damaged, try a fungicide solution, which you can purchase from most paint or hardware shops.

If re-wallpapering, strip the old paper off the wall first and paint the wall with a fungicide solution. When it is completely dry, re-hang the wallpaper using a paste containing a fungicide agent.

If re-painting, use a paint containing a fungicide agent but never paint directly over existing mildew.

When the mildew has been removed, ensure it does not recur by keeping your home warm throughout and moderately ventilated.