Mould Contamination in Your Home

Article by: Victoria Rochon, P.Eng, MBA.

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All indoor biological contaminants originate from our surrounding environment. Although mould naturally occurs outdoors, the outside environment is a large and therefore diluted atmosphere. The problem begins when mould contaminates our indoor environment. Indoor air allows the development of a high concentration of contaminants unless an adequate air exchange rate between the indoor and outdoor atmosphere is maintained. You can minimize the growth of mould in your home through proper moisture control by maintaining good hygiene and cleanliness.

Mould is classified under the Kingdom of Fungi. Fungi are a more advanced life form than bacteria and viruses. Mould spores range from approximately 10 to 80 microns in size. All moulds are allergenic and several hundred moulds are toxigenic. Toxigenic moulds are capable of producing a toxin or poison.

However, this does not mean that toxigenic moulds are producing toxins all the time. The production of toxins depends on the mould’s time in its life cycle, its food source, external conditions (ex. temperature, humidity, and amount of available water), and other factors.

Moulds grow over a range of temperatures. Each type of mould has their own optimum growth temperature. Relative humidity plays a large role in mould growth. A high relative humidity means that there is a high water activity (a high amount of moisture available for use). Each type of mould also has its own water requirement that needs to be met.

Mould is highly pervasive and can easily contaminate the air. One square foot of mould infected drywall can contain more than one billion spores. Most mould spores are light and friable, so they break apart easily and can be carried with water droplets and dust in the air, on people and pets, and through the heating and ventilation system to other locations in your home.

A water loss in your home can induce mould growth. Water losses can include flooding, leaks in building assemblies or plumbing, excess humidity, containment that prevents moisture escape, and more. Moisture control within the wall assemblies of your home is vital. Water entering into the building assemblies can cause the mould spores to germinate, resulting in active mould growth.

Mould growth occurs when there is a moisture source, lack of ventilation, absence of ultraviolet light, and an organic substrate. Mould will grow 24 to 48 hours after a water loss. Lack of proper ventilation allows the substrate to remain hydrated by preventing it from drying out.

Overall, mould contamination in your home can cause degradation of textiles, damage to building materials, and disease in people, animals and plants. Common symptoms in people include: headaches, cough, congestion, fatigue, difficulty concentrating, and irritation of the eyes, nose and throat.

It is very important to maintain a proper indoor environment to prevent the growth of mould. This can be done by ensuring proper ventilation, relative humidity, temperature, and hygiene in your home. The relative humidity should be maintained between 30-50%. Areas with sources that generate moisture (ex. bathrooms, kitchens and laundry rooms) should be properly vented. In addition, cold surfaces should be insulated to prevent the production of condensation (ex. pipes, windows, exterior, roofs, floors, etc.). You should also ensure that your house’s heating, ventilation and air conditioning system is in good working order.

Any water losses that occur in your home should be cleaned up within 24 hours to prevent the growth of mould. Mould will continue to grow if it is not properly treated. When mould spores are disturbed and become airborne, they can spread to other locations in your home and cause respiratory illness. Our experts will complete an in-depth mould and air quality inspection to determine the origin and cause of the contamination. We will also prepare a remediation procedure to properly remove the mould contamination to prevent additional growth and/or future health issues. Roar Engineering can help you restore your home’s impacted areas to a healthy living condition.

If you have any questions regarding mould contamination, please contact Victoria Rochon or Michael Rochon by phone at 1-844-235-8565 or by email at or

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