Three conditions have to be present for the growth of mould:

  • Mould spores
  • A surface with sufficient foodstuff to maintain life
  • A source of moisture

Mould spores are present everywhere in the air around us, and there is nearly always a food source available; for example, cooking fumes or even dust can be sufficient. Per day, an average household generates large amounts of moisture from normal activities. For example: cooking 3 litres, dishes 1 litre, showers/bath 1.5 litres, washing clothes 0.5 litres and drying clothes 5 litres. Add to this up to 4 litres per person, per day, from breathing and perspiration.

Heating with gas or kerosene heaters also produces a lot of moisture: 1 litre of kerosene produces 1 litre of moisture and a 2kW gas heater produces 1 litre of moisture every 1.5 hours.


To prevent moisture build-up, there needs to be adequate heating and ventilation. The interior temperature should ideally be maintained at 18°C to 22°C. Creating air movement will keep the relative humidity at a manageable level. This ventilation can be achieved by leaving windows open a centimetre or two. It’s better to ventilate little and often, rather than in short vigorous bursts.

Window glass is a good guide; if it starts to show more than a minimum of condensation, the windows should be opened a little further.

Remember you’ll still need to ventilate your home in the winter months, even though you may think the house needs to be sealed to prevent heat escaping.

Controlling and reducing household mould growth

Areas of the house prone to mould are those with:

  • Condensation or high humidity, such as the kitchen, bathroom and laundry
  • Restricted ventilation, such as in corners and cupboards
  • Reduced dry heat. For example, in winter, if the inside temperature is lower than the outside temperature
  • Ineffective insulation in walls and ceilings

Steps to reduce mould and growth heating

Condensation and mould growth can be reduced by providing a continuous low level of dry heat. Continuous, even heating will allow warmth to penetrate the walls and ceilings. On cool days, try to keep the inside temperature at least 5°C higher than the outside temperature.

Keep windows and walls dry by:

  • Ventilating rooms by opening windows or doors, or by using extractor fans
  • Wiping away condensation
  • Heating rooms with dry heat

Family room / lounge

Reduce air moisture by:

  • Opening curtains and blinds during the day
  • Opening windows and doors when possible


Reduce moisture and humidity levels by:

  • Using an exhaust fan or opening a window when cooking
  • Using lids on pots and saucepans
  • Checking plumbing for leaks


• Open a window or door, or use an exhaust fan when having a bath or shower

• Clean and dry surfaces that regularly get wet


Reduce air moisture by:

  • Hanging wet clothes outdoors
  • Opening a window when using the drier or venting the drier outside
  • Opening a window or door when using hot water

Cupboards and bedrooms

  • Open curtains to warm rooms with sunlight
  • Ensure clothes and shoes are dry before putting them away
  • Keep bedrooms and cupboards uncluttered and well ventilated
  • Do not press beds hard against bedroom walls – keep a gap for air circulation

Storage space

  • Dispose of any wet, badly damaged or musty smelling items
  • Store dry items in sealed plastic containers
  • Maintain good air movement in storage areas

Removing mould

Mould should be removed as soon as it appears.

Small areas of mould can be cleaned by using a bleach mixture (1 part bleach to 3 parts water) or a suitable commercial product such as Exit Mould. Make sure to follow the manufacturer’s instructions, wear rubber gloves and keep the area well ventilated. Take care not to splash the cleaning solution on yourself or other surfaces.

Do not dry brush the mould, as a brush can flick mould spores into the air, which may cause health problems.