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Mould Contamination
in Buildings Q & A
What is mould or fungus?
Why worry about mould growth in buildings?
What are the possible health effects of mould exposure?
Who is at risk?
Are there regulations or guidelines that apply to control of mould in buildings?
How would I investigate a potential mould problem?
How can mould growth be prevented?
What can be done to remedy a mould problem?
Where can I get more information or advice?
What is mould or fungus?
 The term mould refers to a wide range of microorganisms that are part of the Fungi kingdom of living matter. Most mould organisms live on the surfaces of dead organic material and reproduce by the production of abundant spores. Moulds are found throughout the natural world, and are essential for the recycling of organic material in our forests, lawns and gardens. All require relatively damp environments to grow. In buildings, mould growth is most commonly found on the surfaces of drywall, ceiling tiles, carpet, and wood products that have suffered wetting or prolonged high humidity.
Why worry about mould growth in buildings?
Although moulds are naturally occurring, it is now well established that the growth of mould in buildings can cause a variety of health problems in some occupants.
 Health Canada concluded in a review of the medical literature published in 2004 that living or working in a building with material mould growth is harmful to health. Although different species may have varying health effects, in most cases of mould growth, several types of mould may be growing concurrently. Also, probably all types of mould have the potential of causing allergic responses and in high concentrations would be irritating to most occupants. For these reasons, current standards recommend that all mould growth be considered potentially harmful to health, and abated, without regard to the types of mould present.
What are the possible health effects of mould exposure?
 All moulds have the potential of causing health effects. Moulds produce allergens, irritants and in some cases, toxins that may cause reactions in persons. The types and severity of symptoms depend, in part, on the types of mould present, the extent of exposure, the ages of the individuals, and their existing sensitivities or allergies. Specific reactions may include,
- Allergic effects include hay fever-type symptoms such as sneezing, runny nose, red eyes, and skin rash. Moulds can trigger asthma attacks in persons who are sensitized to mould and may also worsen asthma in non-sensitized people.
- Construction or agricultural workers who disturb significantly mouldy materials are at risk of developing more serious respiratory diseases, including hypersensitivity pneumonitis (often referred to as farmers' lung).
- Mould exposure can cause irritation of the eyes, skin, nose, throat, and lungs, and sometimes can create a burning sensation in these areas.
- A relatively few types of mould can infect the human body, primarily the respiratory tract. Generally, such infections are limited to persons with weakened immune systems. Bird and bat droppings may harbour spores of Histoplasma capsulatum and other organisms that are an infectious risk to even healthy individuals, and should be presumed to pose a serious risk if accessed or disturbed.
Who is at risk?
- Persons with allergies to mould or have asthma may react to the presence of any mould.
- Anyone may react to the irritant or toxic effects of moulds. There is insufficient evidence at this time to establish "safe" exposure levels for airborne mould.
- Infants and young children, individuals with reduced immune function, or those with pre-existing lung disorders, may have a more severe reaction to moulds.
- Maintenance and construction workers in buildings are at risk if mouldy materials or bird or bat droppings are disturbed without appropriate precautions.
Are there regulations or guidelines that apply to control of mould in buildings?
 Municipal public health departments have the authority to issue orders to owners of public buildings and rental housing regarding potentially hazardous mould growth. Some municipalities have already acted on this issue by ordering the building owner to inspect for and abate any hazardous mould. The public health department may order that the affected areas remain unoccupied until the remediation is complete.
Health Canada issued guidance in 1995 and 2004 for the assessment and control of mould growth. The Ontario Ministry of Health has issued guidelines for the management of mould in school portable classrooms.
The Ontario Ministry of Labour has issued guidelines and a Hazard Alert on mould in buildings. To quote the Ministry 2000 Hazard Alert, "The sustained and/or extensive growth of any visible mould on the interior surfaces of a building is unacceptable. Mould growth on the interior surfaces of buildings is a risk factor for health problems."
Employers and constructors are responsible under the Occupational Health and Safety Act to take every reasonable precaution to protect workers, and this includes protecting workers from mould in workplace buildings. The Ministry recommends that building managers and employers follow current professional standards for mould control. The Ministry has issued multiple orders for assessments of possible mould contamination, and remediation when mould is identified, and has upheld refusals to work where mould contamination in buildings was suspected or confirmed.
Good advice is also available from a number of professional standards and guidelines.
How would I investigate a potential mould problem?
Suspected mould problems can be difficult to investigate, especially since the reported signs and symptoms have many other potential causes, such as poor air quality, seasonal allergies, and common infections such as colds and the flu.
 In order to separate mould concerns from other issues, you should consider at least the following lines of investigation. If this is a workplace, the Joint Health and Safety Committee or safety representative must be informed of the investigation, has a right to observe the testing and must receive reports.
- Health investigation: The investigator should gather information from the occupants or employees regarding any problems they might associate with the building. Of special concern would be reports of headache, nose or throat irritation, chronic respiratory infections, rash, allergy-like reactions, or fatigue, especially if these symptoms clear when out of the building.
- Building inspection: The investigation will consider the history of roof leaks, leaking pipes, floods, wet basements, etc. Note signs of water damage, stained surfaces or deterioration, or musty odour. Although the water problem may have been fixed, the hazard will remain until all the contaminated material is abated, since the mouldy materials remains hazardous even after the surfaces have dried and further growth has stopped. The hazard is not abated until the water problem is fixed and all contaminated materials are removed under careful controls. The investigator should also consider any possible mould growth within walls or other hidden locations.
- Environmental testing: Surface samples of mould-suspect materials can be tested by microscope examination or culture methods to confirm the presence of mould and the types present. Air sampling is often useful to check for the possibility of hidden growth, within wall cavities, in crawlspaces, within ventilation equipment and ductwork, in carpets, etc. The results of indoor air samples are compared to those taken outdoors or in other reference areas, and if substantially different, indicate the growth of mould in the building. The laboratory should be accredited for environmental microbiology by an accreditation program such as the American Industrial Hygiene Association Environmental Microbiology Laboratory Accreditation Program.
How can mould growth be prevented?
Mould growth will not occur if the interior finishes are maintained dry and with an acceptable humidity level. Proper maintenance of the roof and eaves troughs and downspouts, caulking, windows, foundation and landscaping will prevent mould growth. In the event of interior floods, mould-prone materials should be dried within 24-48 hours to ensure mould growth does not occur. The relative humidity in all areas should be maintained below 60% by ventilation, heating and dehumidification, if necessary.
What can be done to remedy a mould problem?
 Small areas of fungal growth can be removed by the homeowner or a maintenance worker. The underlying moisture problem must be fixed first, or else the mould will grow back. The area should be isolated, a respirator with high efficiency filters is worn, porous mouldy materials are removed, and all surfaces in the area are cleaned with a disinfectant solution and clear water.
Note that authorities advise specialized help for the clean-up of more than a few square feet of mould growth. Special containment, ventilation and safety measures are required for large scale work, and if the work is performed incorrectly, the situation can be made worse. Current standards advise that these larger scale mould abatement projects be supervised by an independent health and safety professional.
Where can I get more information or advice?
For more information, you can contact:
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