Mold in Crawl Space: What’s the Cause and What to Do

Finding mold in your crawl space is bad. Removing mold only to see it return due to the source not being addressed is insane. I read all over the internet steps for removing mold. Many of the steps are great ideas and would be very effective except most don’t cover addressing the source. It makes zero since to rid your crawl space of mold and not fix what caused it. That to me lines up with the definition of insanity. But there are misinformed contractors and homeowners that do it all the time. Hopefully this information ill help you avoid hiring a negligent or uninformed contractor when addressing crawl space mold.

What Causes Crawl Space Mold

If you own a home with a crawl space in a humid part of the country, chances are your crawl space has or had mold. Mold in crawl spaces is very common due to the crawl space being unconditioned. That means there is no active way of controlling temperature or humidity or both.

Crawl spaces are built cheaper many times versus basements or slab style homes. Less dirt to move or remove makes the construction cost less in many instances. They are also built the same way they have been built for decades. Building materials in the crawl space and home has changed but many are reluctant to change the building practices.

New HVAC May Cause Mold in Crawl Space

Installing a high seer rated HVAC system in a home with ductwork running through the crawl space with no conditioning is just asking for trouble. I have seen older homes with crawl spaces explode with mold after the HVAC system has been updated. The new units run colder and more efficient. This creates colder ducts but the air from outside is warm and humid. Warm humid air enters the crawl space unrestricted. Once that warm humid air hits that cold duct, humidity shoots through the roof.

High humidity in a crawl space begins the mold growing process. The humidity is absorbed by the wood subfloor and joists. That wood becomes saturated. I have literally seen wood so wet, it drip water, no joke. Wet wood grows mold. This is a brief overview of why you have mold in your crawl space.

Flooding May Cause Mold in Crawl Space

There are other factors like leaking plumbing and flooding which can also contribute to wet wood. That being said would you hire a contractor to fix the mold problem and allow your toilet to keep leaking water in the crawl space? Of course not. So why would you hire someone to address mold and not fix the humidity problem?

Step 1 to Fixing Mold Problems

This goes for the living space attic, basement, crawl space, wherever…fix the humidity problem first. Homeowners have been taught over the years to control humidity in crawl spaces with fans or more vents. That’s like saying, if your hot and it’s 90 degrees outside, you should open more windows. It is illogical.

This is my most asked question on YouTube and our website. Do I need a dehumidifier? It goes like this. I know you said all crawl spaces need a dehumidifier but my situation is different. I agree no crawl space or situation is ever the same. But if you have mold in your crawl space and the humidity in your area reaches above 60% at any time. You need a dehumidifier in your crawl space.

There is something to be said that all crawl spaces may need a dehumidifier. Even in low humidity climates. Granted they may only run a few weeks a year. But, mold only needs 24 to 48 hours to grow. Installing a dehumidifier is the best way to ensure the humidity is actually controlled in my opinion.

The Second Step in Addressing Crawl Space Mold

Give the crawl space time to dry. Installing a dehumidifier on day 1 and immediately beginning mold remediation does not help. We see companies do this all the time. Sure the dehumidifier is in the crawl space and may or may not be running. But the wood is still wet and a source for mold to grow. Performing mold remediation on wet wood is a good way to ensure the mold comes back quickly. Remember, only 24 to 48 hours is needed for mold to grow.

I actually learned this the hard way. We used to be like everyone else and start mold removal day 1. I had a crawl space that was so wet, by the next day the mold returned. We went in, scrubbed off all the mold with Anabec Advanced Cleaning Solution Plus but failed to follow the instructions. The wood looked great until the next morning. The mold was not as thick as before but definitely noticeable. That is when we changed our mold protocol to ensure the wood moisture level was at least under 20% per Anabec’s instructions. We don’t care if it takes 2 days or 2 weeks, the wood must be dry.

Mold Removal is a Difficult Process

Removing mold in a crawl space is a difficult and expensive process. It requires air scrubbers, in our case soda blasters, mold cleaners, mold preventatives and plenty of PPE (Personal Protective Equipment). Tackling this project is not for the average DIYer. But it can still be done effectively IF done in the correct sequences and you use the correct materials or products. If you are not sure about addressing the mold yourself, hire a great contractor to assist you. If you want to tackle crawl space mold, check out our DIY store for products and PPE.

Steps for Removing Crawl Space Mold

Here is an overview of some steps that should be taken to address mold. This is not a mold protocol. Every crawl space is different with unique situations. Hiring an experienced professional is recommended.

Dry the crawl space wood, at least below 20%
Ensure humidity is kept below 60% forever
Fix plumbing leaks
Removing/dispose of subfloor insulation
Scrub, HEPA vacuum or soda blast visible mold to remove it
Apply a mold cleaner or disinfectant
Apply mold preventative
Use proper containment, air scrubbers, etc to ensure mold does not move to other areas