Household Mould—Where it grows, how to avoid it, how to deal with it

Moulds are particles of fungus that result from the breakdown of dead plants and animal matter. Though most commonly found outdoors, mould spores can travel or be carried inside buildings. There, they can grow rapidly, providing they find warmth, moisture and fuel, such as wood, ceiling tiles, drywall, fabric, and even plant soil.

Mould (or mold) comes in many forms, ranging from the good mould in penicillin or your blue cheese, to mildly problematic and worse. Moulds can trigger allergy symptoms such as irritated eyes, sore throats, congestion, and for some, troubles with breathing. But that’s not all; the effects of certain mould species have been linked to severe medical conditions. Let’s just say it’s best to keep mould from developing inside the home.

Avoid moisture in the home

The first step to preventing mould from taking hold is to prevent moisture from building up. Look for leaks around roofs, appliances, windows, plumbing fixtures, or areas where flooding, spills or seepage have occurred, then take the steps to fix the problems. The important thing is to control the level of humidity. Levels of humidity above 60% can actually promote the growth of mould.

Next, ventilate damp rooms, especially the kitchen and bathrooms, and check the quality of the grout among wall, counter and floor tiles. Deteriorated grout allows moister to penetrate behind the tile and into the surface beneath, where mould can develop.

Allowing shower curtains to dry outside the tub after use is a way of preventing mould buildup. Don’t leave wet clothing sit in the washing machine, as mold can grow quickly, and keep the lid of the washing machine open until the interior is completely dry.

If you have dirt crawlspaces in your home, the floor should have a vapour barrier and the space should be properly ventilated.

Finally, use the chart below to set your humidifier depending on the temperature outside. Improper humidifier settings can lead to condensation on windows and skylights. These can lead to water-related damage and mould.

Indoor Relative Humidity Levels that will keep thermal pane windows condensation free

Outside Air Temperature (°)

Maximum Indoor Relative Humidity at 20° (68°)

-30° or below15%
-30° to -24°20%
-24° to -18°25%
-18° to -12°35%
-12° to 0°40%

Addressing mould issues

Eliminating the water issue is key to eliminating mould, so start there.

Mould growth can occur in as little as 72 hours. If you have mould, the safest thing to do is to hire a professional to deal with the issue and prevent it from spreading to other areas.


Household Mould—Where it grows, how to avoid it, how to deal with it