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That damp, musty smell you notice when you walk into a room? It’s not just infuriating, it’s most often the first sign that mould is growing indoors, somewhere you can’t see. Maybe it’s in the rear of the drywall, under the carpet, in the attic, or deep inside the HVAC system. And once mould gets started, it grows rapidly.
Mould in your home isn’t just ugly. It’s an indication that water has sat around too long, and that can lead to expensive damage to your house and your body. For homeowners in Toronto and the GTA, understanding why mould forms and how to stop it is the solution to protecting your home, your investment, and the air you breathe.
With DGI Waterproofing, you receive affordable mould removal that fixes the source of the problem, not just the surface. We’ve seen firsthand how quickly mould can advance when water problems go unaddressed, and we know exactly how to professionally remove mould.
If you have indoor mould or want to prevent it before it occurs, you’re reading the right blog. Here we’ll discuss the most common indoor mould causes and provide practical prevention advice.
What Makes Indoor Mould a Serious Problem
Mould is a natural form of life, it’s everywhere. But once it starts to grow inside, then it’s a problem. The real problem isn’t necessarily the mould, but the conditions that allow the mould to grow. Mould needs three things to grow: moisture, heat, and organic matter. Which means wherever there is water damage, leaks, or excessive humidity, mould can come in and make itself at home.
The Core Causes of Indoor Mould Growth
1. High Indoor Humidity
Humidity above 60% is a breeding ground for mould. Bathrooms, laundry rooms, and basements are all hotspots where humidity tends to linger. In places like Toronto, where we experience humid summers and damp winters, it’s crucial to manage indoor air quality properly. Without dehumidification or ventilation, mould colonies can form quickly and remain undetected until they’ve done serious damage.
Prevention Tip:
Use dehumidifiers in problem areas. Keep exhaust fans running in bathrooms and kitchens. Consider installing a whole-home dehumidifier or an HRV (heat recovery ventilator) system for consistent air exchange.
2. Leaks and Water Intrusion
Leaking roofs, foundation cracks, burst pipes, any access of unrestrained water intrusion will lead to mould. Water seeping in around basement walls due to improper drainage or foundation cracks is one of the most common issues we encounter at DGI Waterproofing. It’s often weeks before anyone knows there’s a leak once water gets behind drywall or in subfloors. By then, mould has taken hold.
Prevention Tip:
Inspect the areas around sinks, around the appliances, around windows, and especially your basement foundation regularly. If you spot staining, bubbly paint, or a consistent odor, get it professionally inspected.
3. Poor Ventilation
The ideal location for mould is a room with poor air circulation. Range-hoodless kitchens, exhaust-fan-less bathrooms, and window-closed basements generate stale, moist air that the mould loves. Poor ventilation not only raises humidity but also fails to dry out water intrusions, hence perfect conditions for spores to grow and multiply.
4. Flooding and Sewer Backups
This is a no-brainer, but it’s worth repeating. Any sort of flooding, be it from a storm, sump pump failure, or sewage backup, increases the risk of mould exponentially if the water is not removed quickly and properly. Even after visible water is removed, moisture in subfloors, drywall, and insulation remains, and mould can start to grow in as little as 24 to 48 hours.
Prevention Tip:
Invest in a sump pump with a battery backup. Ensure downspouts are directing water away from the home. And if flooding happens, don’t delay, call professionals immediately for water extraction and drying.
5. Condensation
Condensation is a silent contributor to mould growth. It forms when warm, moist air meets cold surfaces like windows, metal pipes, or poorly insulated walls. If condensation is frequent and not wiped away, the constant dampness creates a prime location for mould, especially in older homes with minimal insulation.
Prevention Tip:
Insulate pipes and upgrade old windows. Use storm windows or window film in winter. Keep interior doors open to promote even airflow and reduce cool, stagnant pockets where condensation can form.
Health Risks Associated with Indoor Mould Growth
While the visual and structural damage from mould is frustrating, the health effects can be even worse. Prolonged exposure to indoor mould can cause or exacerbate respiratory conditions, particularly in children, the elderly, and those with weakened immune systems.
Common health symptoms of mould exposure:
- Persistent coughing or wheezing
- Runny nose, itchy eyes, or skin rashes
- Headaches or unexplained fatigue
- Aggravation of asthma or bronchitis
- Increased illness frequency
Symptoms include coughing, sneezing, eye irritation, and even skin rashes. In severe cases, mould exposure can lead to chronic respiratory issues or allergic reactions. That’s why mould removal isn’t just about property maintenance, it’s about protecting your health.
Common Places Where Mould Hides in Homes
Location |
Why Mould Grows Here |
What to Watch For |
|
|---|---|---|---|
| 1 | Basements | Poor drainage, high humidity, and foundation leaks | Musty smell, damp floors or walls |
| 2 | Bathrooms | Constant moisture, inadequate ventilation | Black spots on tiles or the ceiling |
| 3 | Kitchens | Steam from cooking, plumbing leaks | Mould under sinks or behind appliances |
| 4 | Attics | Roof leaks, poor insulation | Discoloured wood or insulation |
| 5 | Crawlspaces | Ground moisture, lack of airflow | Damp earth smell, visible growth on beams |
| 6 | HVAC Systems | Dust and moisture in ducts | Musty odour when the system runs |
How to Prevent Indoor Mould Growth
We’ve seen it time and again: most mould problems start small and silently. That’s why prevention is the most powerful tool you have. Mould doesn’t need an invitation, it only needs the right conditions.
1. Inspect and Repair Leaks Immediately
Don’t let a small drip turn into a costly mould infestation. Regularly check under sinks, around toilets, near washing machines, and inside cabinets for signs of water damage. If you notice discolouration, swelling, or musty smells, act fast. Waterproofing leaky basements, patching roof leaks, and sealing plumbing lines can stop the problem before it begins.
2. Control Humidity Levels
Keep humidity below 50% year-round. Use dehumidifiers in basements and other damp areas. Invest in a good-quality hygrometer to monitor indoor humidity. Bathrooms and kitchens should always have ventilation fans, and they should be used during and after use to exhaust moisture.
3. Improve Ventilation Throughout the Home
Good airflow helps reduce condensation and dries out damp spots quickly. Open windows when weather allows, use ceiling fans, and make sure furniture isn’t pushed up against walls, especially in basements. If possible, consider a heat recovery ventilator (HRV) system, especially in sealed homes.
4. Waterproofing Basements and Foundations
One of the most effective long-term solutions for mould prevention is waterproofing. DGI Waterproofing provides full basement waterproofing services in Ontario, designed to prevent water from entering your home in the first place. From interior weeping tile systems to exterior waterproofing membranes, these solutions go beyond a temporary fix, they target the root cause of moisture intrusion.
5. Clean and Dry Wet Areas Immediately
Spills, leaks, and floods need immediate attention. Anything wet for more than 24 hours is at risk of mould. Dry carpets, upholstery, and building materials as quickly as possible. In the case of flooding, professional water extraction is the best option.
6. Use Mould-Resistant Materials in Renovations
When renovating, opt for mould-resistant drywall, paint, and insulation. In areas prone to moisture, such as bathrooms and basements, these materials can be the first line of defence against mould growth.
What Does Mould Remediation and Removal Cost?
Mould remediation and removal pricing vary significantly depending on the severity, location, and size of the contamination.
| Service | Cost | |
|---|---|---|
| 1 | Small-Area Mould Treatment | $1,000 – $3,000 |
| 2 | Moderate Mould Remediation | $5,000 – $15,000 |
| 3 | Severe Whole-Home Remediation | $20,000 – $100,000+ |
| 4 | HVAC Cleaning (if contaminated) | $700 – $2,000+ |
*All prices are estimates and can vary depending on the severity, location, and square footage affected.
These aren’t inflated numbers, we’ve seen jobs easily hit the higher range when mould has gone unchecked for months or years. That’s why early detection and waterproofing can save tens of thousands down the road.
Why DIY Isn’t Always the Best Option
There’s a common misconception that a little bleach and elbow grease can take care of mould. The truth is, surface cleaning rarely eliminates the root cause. Mould remediation and removal should be handled professionally when:
- The mould covers an area larger than 10 square feet
- There’s a history of water damage in the home
- The affected materials include drywall, insulation, or flooring
- Residents are experiencing health symptoms
DGI Waterproofing doesn’t just remove the visible mould, we assess the full extent of moisture intrusion, repair the source, and restore the space so it’s safe and healthy again.
Signs You Need Professional Mould Remediation and Removal
- A persistent musty smell, even after cleaning
- Discolouration on walls, ceilings, or floors
- Water stains with no known source
- Health issues that improve when away from home
- Previous water damage that was never fully dried out
If any of these ring true, don’t wait. Delayed action can lead to deeper damage, higher costs, and long-term health risks.
The Hidden Financial and Health Cost of Ignoring Indoor Mould
Mould doesn’t just quietly damage drywall or leave behind ugly stains. It chips away at your home’s value and your family’s health, often without being noticed until it’s too late.
According to Health Canada, around 50% of Canadian homes test positive for dampness and indoor mould, highlighting just how widespread and underreported the issue is. That’s nearly 1 in 2 homes, and many of those households don’t realize the impact it’s having until symptoms show up or the damage spreads behind walls.
From a real estate perspective, the numbers are just as alarming. The Appraisal Institute of Canada (AIC) notes that environmental and biomedical conditions, such as mould, are considered detrimental conditions that can affect property valuations. Home inspectors are trained to look for these signs, and once mould is found, buyers either walk away or lowball hard.
It doesn’t stop there. Insurance companies are also paying close attention. If your policy includes exclusions for mould-related damage (as many now do), claims may be denied if they determined that it was caused by neglect, like an unresolved leak or poor ventilation. That means you could be stuck footing the entire remediation bill and paying for structural repairs out of pocket.
Protect Your Property (and Your Family) Today!
When mould strikes, time is not on your side. Spores multiply in as little as 24 to 48 hours, and the longer you wait, the worse the damage gets, both structurally and financially. The reality is this: most mould problems don’t start big. They start behind a baseboard. Under a sink. In the corner of a basement after a summer storm.
But if you don’t act, it doesn’t stay small for long.
Whether you’re already seeing signs or you just want to make sure your home stays protected, we can help. DGI Waterproofing offers expert mould remediation and removal in Toronto and across the GTA, backed by decades of experience and a real understanding of how homes work in this climate.
We handle it all, from inspection to remediation to long-term prevention through proper waterproofing and ventilation. Because no one should have to live with mould. Not in their air, not in their walls, and definitely not in their future.
Let’s stop it before it spreads. Let’s keep your home clean, safe, and mould-free from the ground up.