Crawl Spaces: Should You Encapsulate & Dehumidify?

Crawlspace inspection

Crawlspaces are really challenging. If you have a crawlspace foundation, you may be wondering if installing a crawl space dehumidifier is enough to keep mold growth away. Or maybe you’re wondering why encapsulation is needed if there’s already a dehumidifier.

Should You Encapsulate?

Yes, you have to encapsulate the dirt floor. In some climates, the foundation is not very deep and in others, with very cold weather, the foundation will extend below grade several feet.  In either case, the dirt itself needs to be encapsulated.  But keep in mind that even if there’s a deep foundation with lots of earth below the surface, the outside and inside dirt are all connected and carry the same amount of moisture.

Dirt itself has between 95% and 100% relative humidity.  If you doubt it, just get a plant/soil moisture meter that can be used to measure the moisture in the soil.  Check your soil inside and outside as deep as possible for best readings and compare.  This is an example of a meter to consider.  

The reason plants can grow is because there’s moisture in the dirt and typically, even in the desert, there’s humidity in the dirt. This may be below the top surface, so just a few inches below is close to 100% relative humidity or moisture content of 100%. It doesn’t mean it’s wet and mushy, it just means that there’s a lot of moisture stored in the dirt. The dirt goes underneath the foundation wall so it is, in essence, continuous with the dirt inside crawl spaces.  

When it rains -even in the desert it rains at some point- it’s at those times that the ground soaks up all the moisture and then it’s going to spread it everywhere. It’s not going to be only wet outside but also wet inside. The top of the soil may seem dry, but below the top surface, it’s as wet below the surface there next to the wall as it is on the outside on the inside. Read this article about estimating relative humidity in soil.  

Know that the ground is percolating water from rain, run-off from roofs and other surfaces, and from sprinkler systems.  That moisture is basically spreading out in all directions.  Therefore it is critical that the dirt in crawl spaces is encapsulated to keep humidity down and away from the structure above.  In most cases, additional dehumidification is also necessary for unvented crawl spaces.  Unvented, encapsulated dirt floor crawl spaces are the current best practice, though for many years in the past vented crawl spaces were recommended.  Unfortunately, these vented crawl spaces have commonly resulted in moldy and rotted buildings above, which has led to a change in direction for the industry.  

How to Go About Encapsulating

Encapsulating crawl space dirt floors is something that homeowners can do themselves – but beware of toxin exposures.  Sometimes it is best to get a professional to do the job, especially if mold is suspected and remediation is also necessary.  In a new construction situation, it is much easier to create dry spaces at the crawl space level while the building is under construction. Always make sure crawl spaces are easy and comfortable to access for homeowners as ongoing monitoring is necessary to protect both the foundation and the structure from leaks and possible pests, including termites. 

Do NOT encapsulate foundation walls as this can hide damage from poor site drainage and hide potential pest damage such as termite tunnels. Foundation walls are not the same as the dirt floor.  Treat crawl space foundation walls the same way that basement walls or above-ground walls are treated.  Impermeable vapor barriers are only recommended on the soil itself. 

For new construction, waterproof walls from the outside and make sure positive drainage away is created at the entire perimeter of the structure.  Code perimeter drainage requires a slope of 5% which is approximately down 6 inches in 10 feet away.  Look for other blog posts and videos on the topic of drainage at and consider my full Build a Safe Home Course for in-depth lessons on crawlspaces, all foundation types, and the overall home building fundamentals to prevent mold.

If your home does have a crawlspace, I recommend it’s one you can get around in easily.  Make sure it is tall enough to do work in, if necessary because ongoing maintenance and checking for new leaks is always a necessity.   Leaks can happen that didn’t happen before, or something changes that causes leaks either from above or from outside.  We want to catch those events early!   

Crawlspace Best Practices

The best practice is to design crawl spaces and treat them like short basements – dry basements.  I actually prefer basement foundations that are built well to any other foundation type whenever possible.  With basements, there’s a good chance somebody’s going to go down there and look around regularly. If a leak begins it can and should be addressed as soon as possible.  Other foundations can leak just the same as basements but no one is noticing.  That excess water that is unmanaged will cause eventual damage for foundations of ANY type.  

If a foundation is leaking in the basement, it’s possible to notice it and then you can address it. But a foundation leaking through the wall into a crawl space or under a slab is just as bad as if it’s a basement foundation leak.  Any unmanaged moisture infiltration, whether seen or unseen will raise humidity levels in the home and can wick into building materials.  That moisture can also be trapped below floor finishes, especially in slab and crawl space homes.  

Learn Moisture Basics To Prevent Mold

Check out my Moisture Basics Mini-Course to learn more about the impacts of moisture on buildings and the Top 10 Defects to check for and avoid to keep your home safe!

Cheryl Ciecko is an ALA, LEED AP, Licensed Architect who helps homeowners and building professionals create safe homes through online education to prevent mold, water damage, and poor indoor air quality. 


You can find her video masterclasses, online programs, and education subscription options at .


For detailed answers on your specific situation or building project, schedule your appointment for an individual consultation.




The information contained in this presentation is for educational purposes only and is not intended to diagnose, prescribe, treat, or cure any disease, ailment or injury to the body. It is not medical advice. FDA regulations prohibit the use of medical claims in conjunction with the sale of any product not approved by the FDA. Statements made herein have not been evaluated by the FDA. 

Any products, techniques, and/or personal usage tips referred to are not suggested as a replacement for proper treatment from a licensed health care professional. I am not a licensed health care professional and the decision to use or not to use any of this information is the sole responsibility of the listener and/or reader. Everyone is an individual with different body types, different blood types, different body chemistries, and it is important to remember that what works for one person may not work for another person.