Resource Article

Benefits of a Crawl Space Dehumidifier

Blake Heron

Did you know that high humidity can cause or exacerbate a whole host of health issues, including allergies and skin irritations? It can impact your HVAC system’s ability to effectively regulate temperature and make it work harder than it needs to. And humidity can even attract unwanted pests.

Eliminating humidity from a large, uninsulated space may sound like a daunting undertaking. But there are a few straightforward fixes, like installing a crawl space dehumidifier. What solution is right for you depends on the severity of your issue.

If you are experiencing higher than normal levels of humidity inside your home, it could be a result of moist air drifting up from your crawl space. In fact, without implementing proper precautions in the area, these problems are almost inevitable.

Keep reading to find out more about how you can mitigate humidity in your crawl space and your home. It can help improve your quality of life, save on energy costs, lengthen the life of your HVAC system, and protect your home’s structural integrity.

For professional help with crawl space dehumidifiers in the greater Hampton Roads, VA / NC region, learn more about BAY Crawl Space & Foundation Repair at our Home Page, About Us Page, or Request A Quote Page.

Humidity Basics

Humidity is a measure of water content in the air. When you hear about humidity on weather reports, it is referring to “relative humidity.” This is a percentage of the maximum amount of water the air can hold at the same temperature.

The water particles in humid air hold heat, which means humid environments trap heat better than dryer ones. This creates the feeling that the climate is warmer than a dry one at the same temperature.

But some humidity is good. If an environment is too dry, then dust and other particles disperse through the air and cause other problems. A little bit of humidity also is good for your skin and respiratory system.

So, what should the humidity be in a sealed crawl space? A good ballpark range is 30 to 65 percent. Above 65 percent, you will begin to see problems, and anything above 75 percent is cause for concern.

The Problems

You may think to yourself, “I never spend any time in my crawl space. Why would I care if it is damp?” The short answer is that air in your crawlspace or basement can make its way up into your living space through porous wood, flooring, and insulation.

Air at the lowest point in your structure naturally flows to upper levels. This is known as the “stack effect,” the same dynamic as smoke rising up a chimney.

And it means that as much as half of all air in the first level of your home could be some that has migrated up from your crawl space.

There are three main causes of humidity in crawl spaces: 1. From the damp ground 2. From the humid outside air and 3. From groundwater and flooding. In dirt crawl spaces, although the top layer may appear to be dry, moist dirt lies just beneath the surface. It is a constant source of moisture that seeps into your crawl space air.

Most crawl spaces have ventilation that allows air to flow freely in and out of the area. So, if the humidity outside is high, this means the air in your crawl space likely is as well. There are myriad problems this can cause for your home.

House Structure

Humidity in your crawl space means the foundation is more susceptible to mold, mildew, and fungus, which can each cause rot and decay. This can impact support beams and subflooring, which may be in direct contact with the crawl space air.

Humidity also can cause floors to sag and threaten the integrity of your home’s structure. As it moves into your home, it can bring about damage to upholstery, furniture, and clothing.


As already stated, a humid room is more difficult to cool off than a dryer one. Conversely, a dryer environment feels cooler, due to the lack of heat-trapping water molecules in the air.

This also means that more humid rooms are difficult to make comfortable. They can feel warmer than they are, as well as produce a “swampy” feeling.

Humidity can impact air quality as well. Mold and fungus spore in the air can cause breathing issues. It can trigger allergies and irritate your eyes and respiratory system.


Moisture in your crawl space can get the attention of a variety of pests, including dust mites, rodents, and a variety of insects. These include termites that cause billions of dollars in property damage every year, more than natural disasters.

If you have noticed an abrupt insect infestation, it could be the result of high humidity. Addressing the source of the issue could be the first step to eliminating it.

Strain on HVAC System

Excessive moisture in your home’s air also means that your air conditioning system is working harder to compensate. This creates strain, particularly in the summer months when it is already running at full steam.

Some HVAC systems have built-in dehumidifiers. These can help cut down on humidity, but not at the level of a dedicated dehumidifier. And, these components can make your AC unit work even harder, as it tries to dehumidify your home at the same time that it is trying to cool it.

The Solutions

Reducing moisture can help prevent all these problems. There are many approaches to doing so, and each will depend on how significant the problem is in your home.

Note that, if you have standing water in your crawl space, you should address this issue before proceeding with dehumidifying. The same with mold: you should hire a professional to do remediation before you address humidity.

Crawl Space Vapor Barriers

Vapor barriers can help block moisture that rises from the soil in your crawl space. These are plastic liners that cover the entire flooring throughout the space. They block both vapors and moisture from seeping into the air.

One advantage of vapor barriers is that you can install them yourself. It is merely a matter of getting the dimensions of the crawl space, buying the appropriate amount of liner, and installing it in the area. It may require adding stakes through the top of the material, but no adhesives are necessary.

While vapor barriers can do a lot to cut down on humidity from the ground, they won’t fix everything. You can expect to see deterioration over the years so a high quality liner is recommended. Also, vapor barriers do not address humidity circulating into the crawl space through the outside air.

Crawl Space Dehumidifier

Dehumidifiers pull moisture from the air, then cool and condense it. The residual water is either stored in a tank (that you must empty on occasion) or drained through a water line. Dehumidifiers further reduce bacteria, viruses, dust mites, fungi, and allergens found in the air.

You may be wondering, “Can I put a regular dehumidifier in my crawl space?” The answer is ‘No’. Small, portable dehumidifiers are a great, temporary solution for problematic areas of your home, such as rooms with poor ventilation.

But these machines cannot produce the same results as a dedicated crawl space dehumidifier. They are not designed to run constantly or handle the type of extreme humidity that exists under some homes. They may provide some minor relief, but ultimately are dangerous and not meant to operate in a crawl space.

A crawl space dehumidifier will work well in combination with vapor barriers. Together they will be attacking two main sources of humidity: ground and air.

You can install these on your own but the work may be best left up to a trained professional who can determine the best configuration for your home. The size of the right dehumidifier depends on various aspects of the crawl space.

Crawl Space Encapsulation

Encapsulation is the most assured way to address severe and ongoing moisture issues in your crawl space. It involves the installation of a heavy-duty polyethylene barrier that completely covers the crawl space area, including the ground and walls. A waterproofing sealant tape helps seal the ends of the material to create a uniform capsule.

Like the other methods, DIY crawl space encapsulation is possible, but you should be sure you know what you’re doing. If done improperly, the advantages of the humidity solution could be diminished. And the project involves a great deal of prep work to the entire crawl space area.

If you’re in doubt about your installation expertise, it may be best to leave it up to a trained technician. That way you know they are installing the encapsulation materials correctly so that you can see the best results in your home.

Don’t Wait to Address Crawl Space Humidity Issues

Now you have an idea of how a crawl space dehumidifier, in combination with other solutions, can reduce humidity and improve air quality in your house. Installing these can greatly improve your health and quality of life, help you save on energy costs, and even lengthen the lifespan of your HVAC system.

BAY Crawl Space & Foundation Repair serves Virginia Beach, Chesapeake, Suffolk, Newport News, and surrounding areas. We can address any structural or moisture problems you are experiencing in the crawl space, no matter how big or small.

We provide free estimates and consultations. So, you have nothing to lose by talking with one of our trained professionals about prospective solutions to your crawl space humidity problem.

Written By Blake Heron

Blake has specialized in crawl space & foundation repairs for over 10 years (since 2012). His prior engineering and business degrees from James Madison University in VA prepared him for a mastery of problem solving with crawl space & foundation repair issues. He is one of America’s top experts on crawl space encapsulation. As Founder of both ‘BAY Crawl Space & Foundation Repair’ as well as ‘GridLock Foundations’ he is a leading industry expert on crawl space foundation repairs.

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