10 Ways To Prevent Crawl Space Mold + Crawlspace Mold Removal

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Crawl spaces (aka crawlspaces) are often overlooked areas of one’s home. They are totally out of sight and therefore forgotten about. But just like attics, crawl spaces offer an irresistible home for mold. It is very important to understand the ways to prevent crawl space mold as well as what to do if you find it. But first…

What Is A Crawl Space?

A crawl space is essentially a hollow area found under some homes between the ground and the first floor. It’s usually roughly 1 – 4  feet high which is just high enough for someone to enter by crawling, as its name implies.

What Is The Function Of A Crawlspace?

It elevates your home off the ground which in some instances is preferable over a concrete slab on dirt.

It is a convenient and inconspicuous place to contain the “guts” of the house, such as its air conditioning and heater, duct work, plumbing, and electric wiring.

Crawl space with HVAC
Photo Credit: Jesus Rodriquez

Pros Of A Crawl Space

  • It keeps a home a bit safer should a plumbing leak occur in the pipes since they are under the house and not running in the attic or above the ceiling.
  • Crawl spaces are ideal for areas with high moisture or in coastal areas with sandy soil, where excessive water can build pressure against a full basement or concrete slab and find its way into cracks.
  • Good for sloped lots
  • Better for soils like red clay
  • Accessible plumbing and wiring
  • Insect inspections are easier

Cons Of A Crawl Space

  • Takes longer to build
  • Stairs are usually required to enter home
  • Less energy efficient since air flows under the home
  • Subject to pest infestations
  • Prone to moisture and mold growth
  • Cracked foundations can cause house settling
Dry crawl space with no  mold

How Common Is Mold In A Crawl Space?

With the basics out of the way, let’s talk about crawl space mold.

Crawlspace mold is very common. Why? Because the very design of a crawl space creates a perfect environment for mold. It has oxygen, it is dark, there is ample food (dirt, wood, insulation, animal waste), the temperature is comfy, and there is moisture.

There are three types of moisture that enter your crawl space and it is important to understand each one.

Crawl space duct leak and condensation


Originally, building code required the crawl space to be ventilated to use outside air as the main source of moisture control. The theory was to allow an outlet for excess moisture to evaporate. Ventilation can actually make a mold problem much worse. This is because the air inside the crawl space tends to be much cooler than the outside air. In warmer months, this becomes problematic due to the fact that warmer air is constantly flowing into the ventilated crawlspace. When warm moist air comes in contact with cooler air, the warm air cools, releasing moisture in the form of condensation. This provides a continuous source of moisture in the crawl space.

Rising Damp

Rising damp is moisture moving from the ground, traveling upward. This can be a major problem for a crawlspace that has not been encapsulated and protected with a vapor barrier. Not only will your crawl space be wet but this natural flow of moisture can begin to affect the subfloor, beams and foundation allowing water to rise through the foundation and eventually into your home.

Penetrating Damp

This is simply moisture that has made its way into your crawl space from another source including plumbing leaks, irrigation, floodwaters, etc…

Signs You May Have Mold In Your Crawl Space

Over 60% of your crawlspace air flows throughout your home so a seemingly isolated mold issue in the crawl space can compromise your indoor air quality and begin to affect your health. For early detection of crawl space mold, it is imperative to know what signs to look for. 

  • You feel cool air from your crawl space entering your home through the floor.
  • There are water stains or green/pink/black spots showing up around the baseboards.
  • There is an odd odor coming from your crawlspace. Remember – mold can smell like anything.
  • Existing insulation is missing or sagging, both of which can suggest you have a water problem.
  • Patches or clusters of what looks like dirt or powder on the floor joists, posts, girders, and corners of the area.
  • You have an increased number of pests entering your home or have noticed animal activity or scat near or in your crawlspace. When animals gain access to your crawl space they often damage the area which can allow moisture to enter the crawlspace.
  • You live on an elevated water table.
A home inspector checking a crawl space for mold

10 Ways To Prevent Crawl Space Mold

Now that you know the signs of crawl space mold, let’s discuss the ways you can prevent crawl space mold.

  1. Apply Endurance Bio Barrier to your entire crawl space. You can learn more about Endurance Bio Barrier Mold Prevention in this post but in short, it is guaranteed to prevent mold for up to 25 years when applied correctly. NO other product offer mold protection in the crawl space like this.
  2. Dryers should be vented to the outside of your house and not into the crawlspace.
  3. Every 3-4 months, look for leaks around HVAC ducts and plumbing components in the crawl space. Also, check the foundation walls and make sure there are no cracks where water or moisture can enter.
  4. Make sure gutters and downspouts channel at least 6 feet away from the house. If they are any closer than that, water can accumulate near the house and eventually find its way inside the crawl space.
  5. Adequate ventilation is critical to prevent mold in a crawl space. At a minimum, there should be two vents on either side of the crawl space. Ideally you will have 1 square foot of ventilation for every 150 square feet of crawl space area.
  6. Insulate with closed cell, two pound spray foam because it will keep the heat in, as well as act like a vapor barrier to fight against moisture. If you use batt insulation you will need to install a vapor barrier on the warm side of the house. Place insulation tightly against the subfloors in your home so the hot and cold air don’t meet in the middle and create moisture. Secure the insulation snugly with mechanical fasteners. It will likely fall out eventually without fasteners.
  7. Piping in the crawl space should be insulated to prevent pipes from freezing and bursting during cold weather. (See other winterization tips to prevent mold here).
  8. Run a high quality dehumidifier that is sized correctly for your crawl space.
  9. If your properly slope allows for water to pool in your crawl space, install a high quality sump pump as you would in a basement to prevent basement mold.
  10. Do NOT use your crawl space as a storage unit. Clutter provides food for mold as well as reduces air flow. It also gives mold another place to grow.

It is important to note that if you are purchasing a new build home or building your own home, you MUST make sure that the building materials are dry at every stage of construction. Saturation from rain during new construction can lead to mold growth in your crawl space in record time. You have rain soaked lumber and rain soaked soil. What a perfect buffet for mold spores!

Crawl Space Encapsulation – Is It A Good Idea?

Crawl space encapsulation is considered the #1 way to seal out moisture and prevent mold in a crawl space. But does it live up to the hype?

Crawl Space Encapsulation with proper vapor barrier installation
Photo Credit: Tim Ingersoll

Sealing Your Space vs. Full Encapsulation

You may hear the term sealing crawl spaces and encapsulating crawl spaces used interchangeably. While they’re similar, sealing generally means only covering the floor and around 8 inches up the walls. This isn’t going to do squat.

Encapsulation entails covering all of the floors, walls and even the ceiling. Encapsulations will include adding insulation to the walls and access doors as well.

Crawl space encapsulation does work to prevent mold but only if it is installed correctly AND if the correct type of vapor barrier is used. Here are the steps a professional installer or a team of two DIYers need to take to ensure that the crawl space encapsulation is done properly.

  1. Mitigate all drainage, mold, or combustion problems. Do not do anything until you have completed this first step. If you skip this step then you are asking for a heap of trouble.
  2. Add a plastic vapor barrier to the crawl space floor and attach it to the foundation walls, piers, and equipment. Attaching the vapor barrier helps keep moisture out of your crawl space. In addition to walls and piers, you also want to attach the vapor barrier to your air handler or water heater. There should be plenty of overlap between the layers of vapor barrier.
  3. Seal off all vents and openings to the outdoors. You want to prevent humid outdoor air from entering your crawl space. To make that happen, seal off crawl space vents using foam board and spray foam. Attach foam board to the crawl space door.
  4. Add a thermal barrier to the crawl space walls. To further prevent outdoor air from entering your crawl space, attach foam insulation to all crawlspace walls.  
  5. Air seal all the gaps and cracks. The next step is to seal off all remaining gaps and cracks with spray foam. This includes band joists, AC drain line runs, plumbing penetrations, wiring, etc. This step includes sealing all gaps between the crawl space and the floor of your home.

Remember – always maintain a continuous point of inspection to satisfy termite regulations. That way, nobody has to dismantle the encapsulation to inspect for termites.

No two vapor barriers are created equal.

Most vapor barrier sold to the consumer (even the construction grade kind) will puncture easily and is subpar in general.

Polyethylene plastic sheeting stocked at the local hardware store is often thinner, non-reinforced, and could be made out of recycled or “regrind” poly. Regrind poly may contain impurities such as dirt or moisture. In addition, construction grade poly will often degrade within 2-3 years.

Beware of vapor barriers (plastic or visqueen) which can degrade from moisture in the soil quickly. These products are manufactured with “post consumer” recycled materials.

A long term vapor barrier must maintain lifelong integrity by resisting decay, attack by moisture, organisms in the soil, and chemicals. So what’s my pick for the best vapor barrier to use in crawl space encapsulation?

Tuff Scrim Antimicrobial 12 mil String- Reinforced Crawlspace Liner

Although all polyethylene is inherently antimicrobial, this crawlspace liner is specially treated to prevent the growth of harmful bacteria, fungi, mold, and algae. Tuff-Scrim TS12-AM’s antimicrobial additive is blended into the poly to make it non-migratory, wash-resistant, non-toxic, and environmentally safe. Tests have proven that fungi will not grow on, near, or around TS12-AM. In addition this is a very tough vapor barrier that will withstand the test of time. You can purchase it here.

Crawl Space Mold Removal

Crawl space mold removal is VERY difficult and complex. Because you need to remove the moldy material this is not a DIY job. If you attempt to remove moldy subfloor, joists, beams, etc… you can cause a major structural disaster if you do not know what you are doing.

Many mold remediation companies steer clear of removing moldy building materials in the crawl space. Often times you will need a combination of a licensed contractor who is experienced with crawl space issues as well as a mold remediation company.

Dry ice blasting or surface blasting are often times the best options for crawl space mold removal. These approaches are not DIY and need to be performed by a professional mold remediation company who specializes in blasting for mold removal.

These reason blasting is selected over removing moldy building materials is so the structure itself is not compromised. In addition, it can be the less expensive option.

To learn more about dry ice blasting / surface blasting, please check out my post on the topic.

If you have a small mold issue in your crawl space, you can likely trust a contractor and / or remediation company to come up with the best plan to remove the mold. If it is a larger issue, you may want to hire a mold inspector to help you determine the best course of action. The last thing you want to do is not properly address the situation or create a worse situation.

How Much Does It Cost To Remove Mold In A Crawl Space?

The mold in crawl space removal cost can be as low as $500 to as high as $30,000. Factors like the size of the mold issue, the extent of the damage, types of materials that are damaged or infected, and accessibility of treating the mold all come into play to determine the cost.

You might be wondering if homeowners insurance covers mold in the crawl space? No, a typical homeowner’s policy does not cover the cost of mold removal, unless mold infestation is due to a condition that’s covered by the policy, such as flooding and water damage.

Beyond Mold – Other Crawl Space Dangerous

Crawl spaces are not a very desirable place to go. I’ve only crawled through a couple and if I can avoid it, I will never enter one again. They are not for the faint at heart.

Aside from mold, there are quite a few crawl space dangers to be aware of. These include:

  • Radon gas
  • Asbestos
  • Rodents
  • Termites
  • Snakes
  • Other pests or nesting animals
  • Hantavirus
  • Raw sewage / dried sewage
  • Structural collapse 
  • Improper wiring

In Conclusion

Crawl spaces should never be areas that are forgotten about or ignored. Proper mold prevention can save your entire home from an expensive disaster. Most mold related crawl space issues should not be left to DIYers. Instead, bring in a professional who knows how to protect your home and family.

A crawl space with mold

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  1. Braden Bills says:

    I had to go into my crawl space to do some plumbing work, and I noticed that there’s a ton of mold down there! It makes sense that I would want to have things waterproofed to ensure that it doesn’t get worse. It would be a good idea for me to get a professional to help remove the threat of the mold, as well.

  2. Michaela Hemsley says:

    Thanks for pointing out that crawl space encapsulation is the best way to prevent mold from growing in that area. My dad and I were looking around his crawlspace the other day because we realized that no one had looked at it in years, and we noticed that there seems to be a leakage problem in there. I am almost certain that because of that there will be mold there eventually, if there is not already, so I think it would be smart for him to look into encapsulation for that space. That would help him prevent any further problems in that area, I think.

  3. Emily Bennette says:

    I am a little worried about there being mold in my crawl space because it got a little flooded. It is good to know that other things like snakes and mice could be there too. It seems like it would be smart for me to get my crawlspace inspected and repaired by an expert.

  4. Dallas Mold Removal says:

    Crawl space mold is not always readily identifiable, but there is a way that you as the homeowner can spot it. If you happen to have spots of mold in your home, it’s already a big enough problem to consider hiring a professional to get rid of it.

  5. Tacoma Mold Removal Co. says:

    Your crawl space is more susceptible to mold growth than any other part of your home. This is because you hardly visit your crawl space and if you feel that your crawl space is affected, check your crawl space immediately. If you have a serious mold problem, get in touch with a mold removal expert.

  6. Eli Richardson says:

    It really helped when you talked about crawl spaces and why they could get mold very easily! Recently, my wife and I moved into another house, and it came with a crawl space. We want to make sure we don’t have any type of pest or mold infestation, so we’ll be sure to look for a professional’s help! Thanks for explaining to us what crawl spaces are and how to keep mold out from them!