I didn’t think much about my crawl space—until I had to. At first, it was just a faint, musty smell in my home. Then, I started waking up with a stuffy nose and itchy eyes. My floors felt damp, and no matter how much I cleaned, the air inside never seemed fresh.
That’s when I went looking for answers. What I found lurking under my home shocked me—mould spreading across the crawl space like an unwanted guest. It had been quietly growing, feeding on moisture, and creeping into my air supply. I wasn’t just dealing with bad air. I was breathing in mould spores every single day.
If your home has a lingering musty smell, unexplained humidity, or worsening allergies, your crawl space might be the problem. The good news? You can stop mould before it takes over. In this guide, I’ll share 10 effective ways to keep your crawl space dry and mould-free—so you never have to deal with what I did.
Mold Growth in Crawl Spaces
Mould isn’t something that appears overnight. It starts small, almost invisible, and then slowly spreads until it becomes a serious problem. Crawl spaces are the perfect breeding ground for mould because they are dark, damp, and often ignored. If the conditions are right, mould can take hold and begin growing in as little as 24 to 48 hours.
Once mould starts growing, it doesn’t stay in one place. Mold spores travel through the air, making their way into your home. Since about 40% of the air inside your home comes from the crawl space, mould growth below your home means you are breathing it in daily.
Beyond air quality issues, mould can weaken wooden beams, damaged insulation, and create a musty odour that lingers throughout your home. If left untreated, it can lead to costly repairs, making prevention the best solution.
Before we dive into the 10 best ways to prevent mould, let’s first understand why mould thrives in crawl spaces and how it affects your home.
10 Proven Ways to Prevent Mold in Your Crawl Space
Mould prevention starts with one key principle—control the moisture, and you control the mould. If your crawl space stays dry, mould won’t have the conditions it needs to grow. Below are the 10 most effective ways to keep your crawl space mold-free and protect your home’s air quality.
1. Control Moisture Levels to Stop Mold Before It Starts
Mold thrives in damp conditions, so keeping moisture levels low is the most important step in prevention. The key is to manage humidity and eliminate water sources before mould can take hold.
- Use a hygrometer to monitor humidity levels. Ideally, crawl space humidity should stay between 30% and 50%.
- Fix any standing water issues immediately. Even small puddles can create enough moisture to trigger mould growth.
- Avoid storing cardboard boxes, wood, or paper in the crawl space—these materials absorb moisture and feed mould.
By controlling moisture, you’re stopping mould before it even starts.
2. Install a Crawl Space Vapor Barrier for Maximum Protection
A vapour barrier is one of the best defences against moisture in a crawl space. This is a thick plastic sheet that covers the ground and sometimes the walls to prevent moisture from rising into the air.
- Choose a durable, high-quality vapour barrier—at least 6 mils thick, preferably 12 mils or higher for better protection.
- Cover the entire crawl space floor, overlapping the seams and sealing them with waterproof tape.
- Extend the barrier a few inches up the foundation walls and secure it to prevent moisture from creeping in.
A well-installed vapour barrier can significantly reduce crawl space humidity, preventing mould before it can develop.
3. Improve Drainage Around Your Home to Prevent Water Seepage
Even if you don’t see standing water in your crawl space, poor drainage around your home can allow moisture to seep in from the outside. Suppose rainwater or groundwater isn’t directed away properly. In that case, it will collect near your foundation and eventually reach your crawl space.
- Ensure gutters and downspouts are clear and functional. Clogged gutters cause water to overflow and soak into the ground near your foundation.
- Extend downspouts at least 6 feet from your home to prevent water from seeping into the crawl space.
- Grade your yard so water naturally flows away from your foundation instead of toward it.
By managing outdoor drainage, you stop excess moisture before it reaches your crawl space, reducing the risk of mould growth.
4. Keep Humidity Low with a Crawl Space Dehumidifier
Even with a vapor barrier and proper drainage, some moisture can still enter your crawl space. The best way to keep humidity levels under control is to use a crawl space dehumidifier.
Unlike standard dehumidifiers designed for living spaces, crawl space dehumidifiers are built to handle lower temperatures and tighter spaces. They continuously remove excess moisture from the air, keeping humidity within the safe range (30% to 50%).
- Choose a high-capacity unit designed for crawl spaces.
- Please place it in the centre of the crawl space for even moisture control.
- Set the humidity level to below 50% to prevent mould growth.
- Clean or replace the filter regularly for maximum efficiency.
Using a quality crawl space dehumidifier adds an extra layer of protection against mould and moisture-related damage.
5. Seal Crawl Space Vents to Block Humid Air and Pests
For years, homeowners were told that ventilating crawl spaces would help with moisture control. The truth is that open crawl space vents often do more harm than good.
When humid air enters through vents, it raises moisture levels, dampening the crawl space and creating the perfect conditions for mould. Vents also invite pests like rodents and insects, which can chew insulation and spread allergens.
To prevent these issues
- Seal all exterior crawl space vents using foam board or specialized vent covers.
- Check for small openings or cracks in the foundation and seal them with caulk or spray foam.
- If you encapsulate your crawl space, combine vent sealing with a dehumidifier to maintain air quality.
Sealing crawl space vents keeps humid air, pests, and contaminants out, preventing mould and improving your home’s air quality.
6. Fix Leaks and Plumbing Issues Before They Create Mold
Even a slow, unnoticed leak can create the perfect breeding ground for mould. If you have water pipes running through your crawl space, a leak in your plumbing system could add moisture to the air without you realizing it.
To stay ahead of potential issues
- Inspect all visible pipes in your crawl space for leaks or condensation buildup.
- Wrap pipes with insulation to prevent sweating (condensation forming on cold pipes in humid air).
- Check for signs of past leaks, like water stains on the vapour barrier or wooden beams.
- Fix any plumbing issues quickly—even small drips can lead to big problems over time.
Eliminating water sources before they cause damage can prevent mould from growing.
7. Remove Organic Materials That Can Feed Mold Growth
Mould needs two things to thrive: moisture and a food source. While moisture control is the first step, you must remove materials that mould can grow on.
Common crawl space mold food sources include
- Cardboard boxes (which absorb moisture and break down easily).
- Old insulation (especially fibreglass, which traps humidity and dust).
- Wood debris left behind from past construction work.
If you store anything in your crawl space, make sure it’s in a sealed plastic container, not cardboard. Keeping the space clean and free of organic materials removes another risk factor for mould growth.
8. Ensure Proper Airflow and Ventilation for a Dry Space
Keeping the air moving in your crawl space is key to preventing moisture buildup. Without proper airflow, humidity gets trapped, creating the perfect conditions for mould to thrive.
- If your crawl space is sealed, use a dehumidifier or an air circulation system to maintain proper air exchange.
- For vented crawl spaces, make sure vents are clear of debris and positioned for cross-ventilation.
- Check for obstructions like fallen insulation or stored materials that might block air movement.
- Use a crawl space fan to improve circulation and help remove excess humidity.
Proper airflow works hand in hand with moisture control, keeping your crawl space dry and mold-free.
9. Use Mold-Resistant Insulation and Protective Coatings
Traditional insulation, like fibreglass, absorbs moisture, making it a breeding ground for mould. If you’re insulating your crawl space, choose mold-resistant materials that won’t trap water.
Best insulation choices for crawl spaces
- Closed-cell spray foam – Seals gaps, blocks moisture and doesn’t absorb water.
- Rigid foam board insulation – Resists moisture and mould growth while providing effective insulation.
Beyond insulation, consider using mould-resistant coatings on wooden beams and foundation walls. These coatings help prevent mould spores from taking hold and protect surfaces from moisture-related damage.
10. Schedule Regular Crawl Space Inspections & Maintenance
Even with all the right preventative measures, routine inspections are the best way to catch problems before they get out of control.
How often should you inspect your crawl space?
- At least twice a year (once in spring and before winter).
- After heavy rains or flooding, check for standing water.
- Whenever you notice musty odours or higher indoor humidity.
What to look for
- Signs of moisture – Condensation, damp insulation, or water stains.
- Mould growth – Look for dark spots on wood, insulation, or foundation walls.
- Leaks and plumbing issues – A small drip can create long-term mould problems.
- Pest activity – Rodents and insects are drawn to damp spaces.
Catching these issues early can save you thousands in repairs and keep your crawl space mould-free for the long haul.
What to Do If You Already Have Mold in Your Crawl Space
If you’ve already found mould in your crawl space, don’t panic. While mould can be a serious issue, it can be removed and prevented from returning. The key is to act quickly before it spreads further.
Signs That Indicate Mold Has Started Growing
Mould isn’t always obvious. It sometimes grows unnoticed for months, silently affecting your home’s air quality.
- Musty or damp odours that don’t go away.
- Increased allergy symptoms like sneezing, itchy eyes, or congestion.
- Visible mould growth—black, white, green, or fuzzy patches on wood, insulation, or walls.
- Discolouration on beams or foundation walls.
- Warped wood or soft spots—moisture weakens wooden structures, leading to sagging floors.
- Higher indoor humidity levels, even with air conditioning running.
- Pest infestations—mould attracts insects and rodents, which thrive in damp conditions.
If you notice any of these signs, you must remove the mould before it worsens.
DIY vs. Professional Mold Removal – What’s Best?
Once mould is in your crawl space, should you remove it yourself or call a professional? The answer depends on the severity of the problem.
When DIY Mold Removal May Work
- The mould is in a small, contained area (less than 10 square feet).
- You caught it early, and it hasn’t spread deeply into wood or insulation.
- There’s no major water damage causing ongoing moisture problems.
Steps for DIY Mold Removal
- Wear protective gear—gloves, an N95 mask, and goggles.
- Use a mould cleaner (a mix of white vinegar and water or a commercial mould removal product).
- Scrub the affected area with a stiff brush until the mould is gone.
- Dry the area completely using a fan or dehumidifier.
- Apply a mold-resistant treatment to prevent regrowth.
When to Call a Professional
- Mould covers a large area or is deeply embedded in wood.
- There’s extensive water damage, and moisture issues haven’t been fixed.
- You’re dealing with toxic black mould (Stachybotrys chartarum).
- You have health concerns like asthma, allergies, or respiratory issues.
A professional mould remediation company will thoroughly remove mould, treat surfaces, and provide long-term solutions to prevent its return.
How to Keep Mold from Returning After Removal
Getting rid of mould is only half the battle. To ensure it doesn’t come back, you need to eliminate the conditions that allowed it to grow in the first place.
Steps to Keep Your Crawl Space Mold-Free
- Fix the moisture source—a leak, high humidity, or poor drainage.
- Install a vapour barrier to prevent ground moisture from rising.
- Use a crawl space dehumidifier to maintain humidity below 50%.
- Seal cracks and gaps in the foundation to stop water intrusion.
- Check for plumbing leaks and repair them immediately.
- Schedule routine inspections to catch issues early.
By taking preventive measures, you can ensure mould never becomes a problem again.
Final Thoughts
Mould in your crawl space can damage your home and indoor air quality. The key to prevention is controlling moisture and keeping the space dry.
Follow these 10 essential steps
✔ Manage humidity with a dehumidifier.
✔ Install a vapour barrier to block moisture.
✔ Improve drainage to prevent water buildup.
✔ Seal vents and fix leaks to stop water intrusion.
✔ Ensure proper ventilation and remove mold-prone materials.
✔ Use mold-resistant insulation for added protection.
✔ Inspect regularly to catch issues early.
If mould is already present, remove it quickly and eliminate moisture sources to prevent regrowth. A dry, well-maintained crawl space means cleaner air, fewer repairs, and a healthier home. Take action today to keep mould away for good.
FAQs
1. What causes mould to grow in a crawl space?
Mold thrives in dark, damp environments. High humidity, poor ventilation, leaks, and standing water create the perfect conditions for mould growth in a crawl space.
2. How can I tell if my crawl space has mould?
Common signs include a musty odour, visible mould growth, increased humidity, warped wood, sagging floors, and worsening allergies inside your home.
3. Can mould in a crawl space affect indoor air quality?
Yes. About 40% of the air in your home comes from your crawl space, meaning mould spores can travel upward, affecting indoor air quality and causing health issues like allergies and respiratory problems.
4. What is the best way to prevent mould in my crawl space?
The best prevention methods include:
- Installing a vapour barrier to block ground moisture.
- Using a dehumidifier to keep humidity below 50%.
- Sealing vents and fixing leaks to prevent water intrusion.
- Ensuring proper drainage around your home.
5. Should I keep my crawl space vents open or closed?
Sealing vents is generally better. Open vents allow humid air, pests, and moisture inside, increasing the risk of mould. Instead, a dehumidifier and encapsulation are used for moisture control.
6. Is it safe to remove the crawl space mould me?
DIY mould removal using a commercial cleaner or vinegar solution may work for small areas. However, hiring a professional for safe removal is best if mould covers a large area or has caused damage.
7. How much does preventing or removing mould from a crawl space cost?
Preventative measures like a vapor barrier and dehumidifier cost between $500 and $3,000, while professional mould remediation, depending on severity, can range from $1,000 to $5,000.
8. Will a dehumidifier alone prevent mould growth?
A dehumidifier helps control moisture but isn’t a complete solution. Pair it with a vapour barrier, proper drainage, and regular inspections for the best protection.
9. How often should I check my crawl space for mould?
Inspect your crawl space at least twice a year, especially after heavy rain or during humid seasons, to catch mould growth early.
10. What is crawl space encapsulation, and is it worth it?
Encapsulation involves sealing the crawl space with a vapour barrier, closing vents, and adding a dehumidifier. It’s a long-term solution that prevents moisture, improves air quality, and reduces mould risks, making it a worthwhile investment for most homeowners.
