Mould

What are moulds?

Moulds are tiny microorganisms belonging to the fungus family, along with mushrooms and yeast. There are thousands of different types of moulds.  At all times of the year, their spores are present in varying quantities in air, indoors and outdoors. Moulds play an important role in helping to compost decaying materials like plants, in the fermentation of food, and in some antibiotics, but they can pose health risks as well.  Most moulds are harmless, but some can cause health problems for some people.

How do moulds grow indoors?

Mould spores can get inside buildings through doors, windows, ventilation, heating and cooling systems, and through small openings and cracks in walls and foundations. They can also be brought in on clothing, shoes and the skin and hair of people and pets.

Mould spores need both a food (nutrients) and a water (moisture) source to grow. Foods available indoors for moulds include dust, pet dander, some building materials, furnishings, and decaying food. Sources of water (moisture) in the home include shower and bath steam, humidifier mist, cooking vapors, plants, aquariums, water leaks or penetration, and even people themselves.
Where do moulds grow?
Moulds usually grow in areas that are damp or humid, such as bathrooms. They can also grow in humidifiers, porous insulation, fan-coil units, and in condensation or drip pans. If building materials get wet and trap water, these surfaces can also support mould growth. These surfaces include drywall, ceiling tiles, carpet, wallpaper, window casings and even building foundations.
How do I know if I have mould in my home?

Common household moulds come in many colours and often looks like a stain or smudge or have a hairy appearance and it may smell musty.

If warranted, conduct a visual inspection of the home looking for signs of mould or excessive moisture, such as stains or discolouration on floors, walls, windowpanes, ceiling tiles, fabrics and carpets. Check for leaks, condensation, flooding or a musty odour.

Mould will begin to grow within 48 hours and can grow behind walls or above ceiling tiles, so an immediate response (within 24 to 48 hours) and thorough clean up, drying, and/or removal of water damaged materials will prevent or limit mould growth. It is important to check for the presence of mould anywhere that is damp and especially where water damage has occurred.

What are health concerns regarding mould?

The level of concern for mould exposure depends on the extent of mould, how long it has been present and the sensitivity and overall health of the residents. Some individuals may be more susceptible to mould exposure than others. For example, infants, children, the elderly, and those with health problems such as breathing difficulties are more at risk from mould and dampness.

Any respiratory health concerns should be discussed with a physician if suspected these concerns are caused by poor indoor air quality. A physician is best suited to determine if your symptoms may be related to environmental factors or some other underlying cause.

If you have mould, how can you clean it up?

Susceptible individuals such as pregnant women, infants, children, the elderly and occupants with asthma, allergies or other health problems should not be in or near the area where the mould is being cleaned up. Avoid breathing in mould or mould spores. Minimum protective gear needed includes the following:

  • Safety glasses or goggles – it is recommended to wear goggles that do not have ventilation holes. Avoid getting mould or mould spores in your eyes.
  • Disposable N95 mask - you can purchase an N95 mask from a hardware store. Make sure that the label says “N95”. Other masks are designed to provide limited protection against dust and are not suitable for protecting against mould exposure. To be effective, the respirator or mask must fit properly, so carefully follow the instructions supplied with the respirator.
  • Household disposable gloves - long gloves that extend to the middle of the forearm are recommended. When working with water and a mild detergent, ordinary household rubber gloves may be used. Avoid touching mould or mould contaminated items with your bare hands.

Bleach is not required to clean up mould.

If you choose to use disinfectants, always ventilate the area and exhaust the air to the outdoors. Never mix chlorine bleach solution with other cleaning solutions or detergents that contain ammonia because toxic fumes could be produced.

You can clean up a small amount of mould if you follow the proper procedures and use the right protective equipment. There may be instances, however, when professional judgment may indicate its use (for example, when immune- compromised individuals are present).

Washable surfaces

  • Examples of washable surfaces are windowsills, wood, hard surfaces and tiles.
  • Scrub surface using a cloth with an unscented soap solution.
  • Sponge with a clean wet cloth and dry quickly.

Concrete surfaces

  • Scrub surface using a cloth with an unscented soap mixed with warm water then sponge with a clean, damp cloth and dry quickly.
  • Remove any carpets or cardboard boxes that have been placed directly on the concrete floor as these may have become damp and allowed mould to grow.

Walls

  • Clean the surface of the wall with a damp cloth using baking soda or a small amount of unscented soap solution. Do not allow the drywall to get too wet. Cleaning with too much water adds moisture to the paper and can damage the surface.
  • If the mould is underneath the paint, the drywall will need to be removed and replaced with new drywall.
  • Painting over a mouldy surface does not kill mould and does not stop it from growing back. Painting only temporarily hides the problem.

Should I test for mould?

There are no regulations or standards for airborne mould or mould spores. As such, sampling cannot be used to check compliance with provincial and federal mould standards.

Health Canada and other public health organizations do not recommend testing the air for mould. An air test does not provide information on health and does not address the cause of mould damage in the house. Knowing the type of mould present is not required to remove it.

Sampling for mould should be conducted by professionals who have specific experience in designing mould sampling protocols, sampling methods, and interpreting results. Sample analysis should follow analytical methods recommended by the American Industrial Hygiene Association (AIHA), the American Conference of Governmental Industrial Hygienists (ACGIH), or other professional organizations.

Information for tenants 

What options are available to a tenant dealing with mould in their rental unit?

  • As a tenant you are responsible for preventing mould growth. Use the precautions listed in the section “If you have mould, how can you clean it up?”
  • If there is a mould problem you cannot resolve on your own, tenants can inform the landlord either verbally or in writing of the concern regarding mould.
  • If the landlord does not respond within a reasonable timeframe (48 hours of notification), the tenant can call 3-1-1 (select number 8) to initiate a case with Bylaw Property Standards.
  • If the tenant is not satisfied with the actions of the landlord, contact the Landlord and Tenant Board. The Landlord and Tenant Board is the authority to settle disagreements between tenants and landlords and can assist the tenant with their rights and responsibilities under the Ontario Residential Tenancies Act, 2006.
  • The Landlord Tenant Board can be reached online or by telephone (1-888-332-3234) Monday to Friday from 8:30 am to 5:00 pm.

Information for landlords

What options are available to a landlord dealing with mould in their rental unit?

  • A landlord can contract a qualified consultant to fully investigate and assess the building, including hidden cavities and surfaces, for signs of water damage and mould.
  • In all situations, emphasis should be placed on ensuring proper repairs of the building infrastructure, so that water damage and moisture buildup does not recur. For example, the building envelope (roof, walls, windows, doors, and foundation) has to be repaired if moisture or water is entering the home from the outside.

How to prevent mould growth in your home?

The key to mould prevention is to remove excessive moisture build-up and control relative humidity levels below 50 per cent through proper home maintenance and by following these steps:

  • Vent appliances that produce moisture, such as clothes dryers and stoves to the outside where possible. Seal the joints in the dryer duct with foil tape and clean the lint tray every time you use the dryer.
  • Use air conditioners and/or de-humidifiers when needed.
  • Run the bathroom fan or open the window when showering or taking a bath. If there is not an exhaust fan, have one installed in each bathroom.
  • Use exhaust fans or open windows whenever cooking, running the dishwasher or dishwashing.
  • Check exhaust fans to make sure there is adequate air movement and that they are vented to the outside and not into the attic. Keep the fan running for at least 30 minutes after your shower.
  • Repair plumbing leaks promptly.

What is Ottawa Public Health's role?

Public health inspectors are available to answer questions pertaining to the information provided on the Ottawa Public Health web page.

Note: Public health inspectors will not visit for the purpose of identifying mould or conducting air quality testing. Ottawa Public Health does not provide comments pertaining to site assessment reports for private homes and rental units.

Resources

The following agencies can provide information on indoor moulds, their health effects, proper mould clean-up procedures, and advice on health problems related to indoor air quality.

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