Safety and first aid

Mould and condensation in your home

Indoor condensation creates suitable conditions for mould growth. It can also damage or discolour:

  • fabric
  • paint
  • wallpaper.

Condensation occurs when heated water converts to vapour. The vapour then cools and changes back into liquid.

When air is humid, condensation will occur at the slightest drop in temperature, for example:

  • water droplets on mirrors
  • windows of an unventilated bathroom.

In most Western Australian homes, indoor condensation is the main source of moisture that causes mould growth.

What is mould?

Mould is a fungal growth.

It can grow in homes when conditions are damp, dark and poorly ventilated, for example:

  • bathrooms
  • kitchens
  • cluttered storage areas
  • flooded areas
  • leaking plumbing pipes
  • outdoor humid environments.

Walls, timber, carpet, furniture and fabrics can harbour mould if they stay damp for extended periods of time.

Health effects of mould

Not all people are adversely affected by mould, but it can emit particles that may cause people to sneeze.

Toxic moulds produce mycotoxins that can be a serious health risk. Exposure to high levels of mycotoxins may lead to neurological problems. Prolonged exposure may be particularly harmful.

Symptoms caused by mould allergy may include:

  • respiratory illness or asthma
  • watery, itchy, red eyes
  • chronic cough
  • headaches or migraines
  • rashes (dermatitis)
  • tiredness
  • sinus problems, blocked nose
  • frequent sneezing.

If you have persistent health problems that may be mould-related, visit your GP. They can refer you to a practitioner trained in environmental medicine, or related specialties, who is knowledgeable about these types of exposures.

Humidity in the home

Humidity in a structurally-sound home may come from:

  • kitchens
  • bathrooms
  • clothes dryers (particularly non-condensing dryers)
  • unflued gas heaters
  • washing machines
  • showers
  • fridge drip trays
  • indoor plants
  • evaporation from your body.

Once water vapour is in the air, it can move around the house where it may come into contact with cooler surfaces and condense.

The most common places for condensation to occur include:

  • windows
  • uninsulated exterior walls
  • room corners.

Note: The corner of a room tends to be cooler and have less air movement.

Moisture can be retained in walls depending on the finish. Many interior finishes retain some levels of moisture. The interior finish is a critical factor affecting mould growth.

Flat paints, plasters and untreated wood are more prone to moisture absorbency than semi-gloss or gloss painted surfaces and treated timbers.

High levels of humidity in the home usually occur due to temporary sources of vapour such as a:

  • boiling kettle
  • hot bath.

However, new houses often have higher indoor humidity levels during the first few years as surfaces dry, such as:

  • the concrete
  • plaster
  • paint
  • wooden furnishings.

Older houses may have ongoing problems with dampness because of structural breakdown such as:

  • broken roof tiles
  • poor cavity wall ventilation
  • rising damp.

Controlling condensation and mould

The main ways of controlling condensation and mould include:

  • ventilation
  • heating
  • insulation
  • removal.


  • Open windows and doors to aerate the home and reduce the humidity level. Attic, basement and crawl spaces should also be aerated.
  • Install and use exhaust fans that are vented to outside air in the bathroom and in the kitchen while cooking. This can eliminate much of the moisture that builds up from everyday activities.
  • Consider installing ventilation over appliances that produce moisture, such as non-condensing electric clothes dryers, portable air conditioners, and kerosene heaters, or leave windows ajar while they are on.


  • Keep indoor moisture low, using dry heaters or dehumidifiers. Relative humidity should be below 60 per cent (ideally 30 to 50 per cent), measured with a humidity meter – a small, inexpensive instrument available at most hardware stores.
  • Maintain low constant heat when weather is cold or wet. Continuous, balanced heating is better than short bursts.
  • Install heating in the bathroom such as heat globes. Condensation forms more easily on cold surfaces, for example walls and ceilings. In many cases, those surfaces can be made warmer by improving insulation.
  • Insulate hot and cold surfaces, such as water pipes.

Removing mould

  • Eradicate mould when it occurs. It is harder to remove when it has been there for a long period of time.
  • Do not dry brush the area. This could release spores into the air which can spread the mould further as well as cause an allergic reaction for some people.

Treatments for mould

It is usually enough to physically remove the mould by scrubbing it off with water and detergent. If the mould grows back there are several natural fungicides you can try:

  • A 3 per cent solution of tea tree oil is effective (2 teaspoons in a spray bottle with 2 cups of water will suffice). Shake well before each use. Note: Tea tree oil can be toxic to cats and dogs so keep well away from pets.
  • An 80 per cent white fermented vinegar solution [mix 8 parts vinegar (available from supermarkets) with 2 parts water].
  • A 3 per cent solution of hydrogen peroxide.

After applying 1 of the recommended fungicides, above, leave for at least 20 minutes, then scrub the area until no mould or mould stains remain. Finally, wipe the surface down with one of the above solutions to remove residual mould and spores.

Do not use bleach to clean mould. Bleach has a high pH level which makes it ineffective for killing mould. It simply colours it, so it looks like it has disappeared.

The only lasting remedy for being mould-free is to:

  1. Find the source of the moisture problem and fix it.
  2. Dry out the water-affected area.
  3. Remove the mould.

Remember: When cleaning mould you must remember to wear gloves, glasses or goggles and a respirator or face mask to protect yourself from mould spores.

General household maintenance


  • Check the roof for leaks and broken tiles regularly.
  • Fix leaky plumbing as soon as possible.
  • Ensure weep holes on the outside of the building are not blocked. Weep holes allow drainage of water and the escape of vapour pressure from internal walls. Over winter and spring the weep holes in window frames (aluminium frames) can get clogged. If clogged, water will stand in the lower window frame sections.
  • Check for doors or windows that may have broken seals.
  • Ensure vents, exhaust fans and air ducts are not clogged.
  • Check for leaky toilets and ensure bathtub and kitchen sink seals are intact.
  • Swollen or crumbling walls or buckling floor boards should be removed.
  • Check for stained ceiling or wall tiles.


  • Clean your bathroom frequently.
  • Ensure clothes and shoes are dry before storing them.
  • Clean evaporation trays in air conditioners and refrigerators frequently.
  • Clean cool mist or ultrasonic humidifiers according to manufacturer instructions and refill with fresh water daily.
  • Wipe away moisture on windows and walls to keep your home dry.
  • Ensure carpets and rugs are regularly aired and cleaned to prevent mould growth.
  • If flooding occurs clean and dry the area immediately to prevent mould growing. Water-damaged carpets and building materials can harbour mould and bacteria. It may be necessary to remove the carpet as the mould may be impossible to remove completely.


  • Allow plenty of ventilation in wardrobes. Leave doors open if possible.
  • If your wardrobe has been affected by mould growth, investigate the source of moisture and treat as soon as possible. Remove mould and allow to dry completely.

Garden maintenance

  • Don’t let the building foundation stay wet. Provide drainage from roof guttering and slope the ground away from the foundation of the building.
  • Ensure garden beds are not higher than the foundation of the building. This will prevent moisture migrating into the wall.
  • Clean roof gutters regularly. Downpipes should drain into soakwells to ensure drainage away from the house.
  • Prune overhanging trees near the roof.

Other tips

  • Use a semi-gloss paint on wooden surfaces. Untreated woods are more prone to moisture absorbency than semi-gloss painted surfaces and treated timbers.
  • Install non-condensing electric clothes dryers instead of standard dryers, or install vents or exhaust fans over standard dryers to carry the moist air outside.
  • Consider installing sky lights in darker areas.
  • Minimise the number of indoor plants.
  • When filling your bath, add cold first, this reduces the steam produced.
  • Let the sun into your home by opening curtains.

Questions and answers

My house has a mouldy smell but I can’t see any mould. Where is it?

It is possible that mould may be growing on hidden surfaces, such as:

  • opposite side of dry walls, wallpaper or panelling
  • roof materials above ceiling tiles (due to leaks or insufficient insulation) – cement roof tiles may lose their outer glaze and absorb moisture into roof spaces
  • underside of carpets and pads, or curtains
  • inside walls, particularly around pipes that are leaking or condensing and drains
  • surface of walls behind furniture, where condensation forms
  • condensate drain pans inside air handling units
  • porous thermal or acoustic liners inside ductwork
  • dry wall (also known as wallboard or gypsum board) covered with vinyl wallpaper  may act as a vapour barrier, trapping moisture underneath
  • insulation
  • wood siding where the paint has cracked and water has intruded.

My carpet has been affected by mould growth and the mould keeps growing back. What can I do?

You need to thoroughly clean and dry your water-damaged carpets immediately.

It is very difficult to completely rid carpets of biological contaminants. It may be necessary to remove and replace the carpet and underlay.

I am renting a property and there is mould growing in the building. What should I do?

Mould and mildew caused by structural faults or leaks should be remedied by the owner.

However, you must ensure there is adequate ventilation and that humidity is kept to a minimum to avoid mould problems in winter.

If you have taken measures to ensure the building is properly heated and aired and mould is still growing, you should raise the issue with the owner or property agent.

If you are seeking further advice, please contact:

  • Western Australian Tenants Advice Service (TAS)
    • Metro Advice Hotline
      9221 0088,
    • Country Advice Hotline
      1800 621 888
  • Consumer Protection
    1300 304 054.

If the mould is severe and you are concerned for your family’s health, contact your local government (external site).

I have heard some species of mould can be toxic. How can I find out what species of mould is in my house?

Mould identification is generally unnecessary, as any excessive amount of indoor mould can be a potential allergen.  However, if you would like to get the mould on your property tested to determine what species it is:

  • speak with your local government environmental health officer
  • search online for a list of environmental or analytical laboratories.

They may be able to assist in species identification.

I have tried everything to get rid of mould, and nothing works. Who can help me?

If you have taken measures to prevent mould from growing in your building and you are still having problems, you may wish to seek the services of a building consultant/building inspector.

Search online for companies who may assist you with advice on structural and moisture damage to your building, including:

  • building inspector
  • mould remediation
  • rising damp repairs.

More information


  • Mould is a fungal growth.
  • Furniture and fabrics can harbour mould.
  • Moisture can be retained in walls depending on the finish.
  • Do not use bleach to clean mould.

Public Health

This publication is provided for education and information purposes only. It is not a substitute for professional advice. Information about a service, product or treatment does not imply endorsement and is not intended to replace professional advice. Readers should note that over time currency and completeness of the information may change. All users should seek advice from a qualified professional for answers to their questions.

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