Mould in crawl spaces is not only a nuisance but also a serious health and structural concern. Hidden beneath your home, crawl spaces often trap moisture, humidity, and organic materials, creating the perfect breeding ground for mould. Left untreated, mould in crawl space can release spores into the air that may cause respiratory issues, allergies, persistent odours, and even long-term damage to your home’s foundation.

This guide will explain everything you need to know—from the causes of crawl space mould, to safe removal methods, and most importantly, how to prevent it from coming back.

Why Mould in Crawl Space Is a Big Problem

Many homeowners ignore their crawl spaces until something goes wrong. But mould in crawl space can:

• Trigger respiratory problems, asthma, and allergic reactions.
• Cause sinus infections, persistent cough, or eye irritation.
• Lead to structural damage as mould feeds on wood, insulation, and drywall.
• Lower indoor air quality throughout the home.
• Decrease property value during resale.

Because air naturally circulates upward from crawl spaces into living areas, ignoring mould growth can compromise the entire home environment.

What Causes Mould in Crawl Space?

The first step in eliminating mould is identifying why it occurred in the first place. Here are the most common causes:

Excess moisture and humidity – Crawl spaces are naturally damp and humid, especially if ventilation is poor. When humidity rises above 50%, mould spores thrive.
Flooding or water seepage – Heavy rains, poor yard grading, or broken sump pumps can cause water pooling under the home.
Plumbing leaks – Dripping pipes or broken drains often go unnoticed in crawl spaces until mould appears.
Condensation – Warm indoor air meeting cool crawl space surfaces leads to moisture buildup.
Poor ventilation – Lack of airflow creates a stagnant environment where dampness lingers.
Foundation cracks – Even small cracks may allow groundwater to seep in, fuelling mould growth.

Without removing the root cause, any mould cleanup will only provide temporary results.

Signs of Mould in Crawl Space

Many times, mould grows unnoticed until it spreads. Look out for these warning signs:

• Musty odour rising into the home
• Damp, sagging insulation or joists
• White, green, or black spots on wood, plastic sheeting, or concrete
• Increased allergy or respiratory symptoms indoors
• Visible standing water or condensation under pipes

How to Get Rid of Mould in Crawl Space

Once you’ve identified mould and the moisture source, you can begin removal. Keep these safety precautions in mind: wear gloves, goggles, and an N95 respirator to avoid inhaling mould spores.

1. Fix the Source of Moisture

Before cleaning, address underlying issues by repairing cracks, leaks, and plumbing problems. Improve drainage or install a sump pump if flooding caused mold, and reduce humidity using dehumidifiers to prevent recurrence.

2. DIY Removal for Small Areas (Under 10 sq. ft.)

Small mould-affected areas can be treated with natural or chemical solutions: vinegar kills many types of mould (spray, leave 1 hr, scrub, rinse); baking soda is a natural deodorizer and mild cleaner (mix with water, spray, scrub, dry); borax is effective but toxic if ingested (spray, leave without rinsing). Always dry the area completely to prevent regrowth.

3. When to Call the Professionals

If mould affects large areas (over 10 sq. ft.) or is a recurring issue, professional mould remediation is recommended. Specialists will use HEPA vacuums, antimicrobial treatments, and negative air pressure machines, remove contaminated insulation, safely dispose of infected materials, and provide a long-term prevention plan.

How to Prevent Mould from Returning

Prevention is more cost-effective than repeated cleanups. Here are long-term strategies:

• Install a vapor barrier: Cover crawl space soil with heavy-duty plastic sheeting to block ground moisture.
• Control ventilation and humidity: Keep humidity levels below 50% using a dehumidifier or crawl space encapsulation system.
• Insulate crawl space walls & pipes: Prevent condensation that feeds mould.
• Encapsulation: Professionally sealing your crawl space with barriers and insulation keeps it dry year-round.
• Check drainage: Make sure water flows away from your foundation with proper yard grading.
• Regular inspections: Inspect twice a year to catch leaks, cracks, or early mould growth before it becomes severe.

Final Thoughts

Mould in crawl space is more than an aesthetic issue—it’s a health hazard and a structural risk. By taking a proactive approach—fixing moisture issues, removing existing mould safely, and installing long-term prevention systems—you can protect both your home and your health.

If your crawl space mould problem is widespread or recurring, don’t delay in contacting a professional remediation company for complete and guaranteed removal.