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High Indoor Humidity

Excessive moisture and humidity in your crawl space can lead to a variety of problems that will impact your home's health and structural integrity. Learn more about why this is happening in your crawl space and what you can do to ensure the safety of your living environment.

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High indoor humidity is more than just an annoyance; it could be telling you that you have crawl space condensation and moisture problems. High humidity can lead to mold growth, rotten floor joists, and high electric bills.

Condensation in the crawl space

Do These Indoor Humidity Pictures Look Familiar?

About High Indoor Humidity

Learn more about what causes high indoor humidity, why you should fix it, and how you can fix it.

The good news is that there are plenty of ways you can fix your high indoor humidity. When you contact a crawl space repair expert, these are the typical steps the expert will go through to help you fix the crawl space humidity problems.  

Remove Standing Water 

The first step to fixing your high indoor humidity levels is to make sure you’ve removed any and all standing water in the crawl space. If you have standing water, the water will just continue to evaporate into the air, causing high levels of crawl space and indoor humidity no matter what other steps you take to avoid the creation of humidity in the area. 

There are a number of ways to remove standing water from the crawl space. An interior drainage system and a sump pump may be a need, especially if you have recurring issues with standing water that may need a recurring fix. Standing water is a problem you shouldn’t try to fix by yourself. Instead, you should consult a crawl space repair expert to handle the water itself and any secondary problems arising from it. 

Close Crawl Space Vents  

Does your crawl space have open crawl space vents? Most homes with a crawl space have crawl space vents because of the widespread belief that these were necessary. Even today, as more crawl space experts are realizing their mistake and starting to recommend against crawl space vents, many residential codes consider vented crawl spaces the default. 

The good news is that it’s actually relatively easy to close your crawl space vents. JES offers crawl space vent covers that you can use to close the crawl space off entirely. This is one of the best ways for you to make sure you’re not letting in excess crawl space moisture, because crawl space vents are responsible for all sorts of issues in your crawl space.  

Install Vapor Barrier System 

A vapor barrier system is an incredibly important part of your crawl space. This is what many people think of when they think of “crawl space encapsulation.” You need to have a crawl space vapor barrier because it’s the piece of the puzzle that ensures moisture doesn’t come up through your dirt crawl space into the rest of your home. 

However, although you do need a crawl space vapor barrier of some kind, it’s important that you install a high-quality crawl space vapor barrier rather than just springing for the cheapest vapor barrier available. JES uses the CrawlSeal™ 20-mil crawl space vapor barrier. This is over three times thicker than the minimum requirement that many crawl space residential codes mandate. 

Add Dehumidifier  

In some cases, it may be important to add a dehumidifier into your crawl space. Although it’s true that this might be an important part of your crawl space encapsulation process, there’s a reason this step goes at the very end. You should never begin your quest to remove your crawl space moisture by installing a dehumidifier because it won’t work if you just put in a dehumidifier. 

You need to go through the process of crawl space encapsulation before you can add a dehumidifier. Once you’ve covered the crawl space vents, added a crawl space vapor barrier, and ensured standing water is no longer a problem, then you can use a dehumidifier to make sure the humidity levels stay stable and healthy. However, if you haven’t done all of these steps, don’t bother with a dehumidifier, because it won’t fix the actual problem you’re experiencing.

Fixing your high indoor humidity isn’t a choice; it’s a necessity. However, a startling number of homeowners don’t realize the importance of fixing their high indoor humidity problems. These are a few of the things you need to think about with high indoor humidity. 

Stack Effect  

The stack effect occurs whenever you have an air entry point at the bottom of a home and an exit point at the top. Attics typically have plenty of spaces for air to leave the home, which means all that’s missing is an entry point below, and that happens if you have poor crawl space encapsulation. The stack effect happens because as air enters the home, it warms up, and because warm air rises, it rises to the top of the home. 

This rising nature is a problem because air isn’t the only thing that’s rising. The air brings along with it anything that can become airborne, including moisture droplets, mold spores, dirt, and sometimes even insect and pest droppings. That’s why it’s so important to encapsulate your crawl space completely, so you can avoid the stack effect. 


Mold is by far one of the most well-known impacts of high indoor humidity. Most people know that if they have high levels of indoor humidity, they’re bound to end up with mold in one area or another. However, you might not know that mold doesn’t need levels in the range of 90% or higher; mold can typically thrive in as low as 60% relative humidity. 

This means that even mildly elevated levels of moisture can be a real problem in your home. Even if you don’t feel like it’s extremely moist in your home, you should still make crawl space encapsulation a priority. You never know whether there might be a warm corner of your home that’s becoming a real hotspot for mold. 

Wood Rot  

Although mold typically doesn’t cause a lot of damage until it’s been left alone for a very long time, wood rot can cause a staggering amount of damage in a very short amount of time. Although it’s typically a fungus much like mold, its impacts are almost nothing like that of mold; it spreads more quickly and more easily than most molds and can be seriously dangerous. 

One of the biggest problems with wood rot is that it basically disintegrates your crawl space structure. Most of the time, you’ll use wood floor joists to keep the home standing up above the crawl space. With wood rot, those floor joists can become dangerously unstable. It’s just one reason you need to maintain your crawl space structure.  

High Electric Bills 

When your home has high indoor humidity, warmth is going to feel much warmer. That means you’re going to want to make the air in your home much cooler than you would have to if you were dealing with a lower level of humidity. Additionally, humid air requires more energy to condition than dry air, making it more difficult to run the air conditioner in the first place. 

These two things combine to create a home that typically will use 15-25% more energy with a humid crawl space than it would with a dry crawl space. In fact, if you’re able to fix your high crawl space humidity, you may save money in the long run, even when you incorporate the cost of the crawl space encapsulation process.

There are many potential reasons for high indoor humidity, and most of them come from your crawl space. Here are some of the biggest reasons you might have high indoor humidity. 

Open Crawl Space Vents 

For a long time, people believed that crawl space vents needed to stay open. In fact, it was a common belief that a vented crawl space was necessary to avoid moisture in the crawl space. The idea was that a vent would “air out” the crawl space, thus making it less likely to succumb to high moisture and other problems. 

However, it’s actually true that open crawl space vents increase the amount of moisture in the crawl space, rather than decreasing it. Open crawl space vents allow cool air and warm air to meet, which increases the relative humidity in that area, typically above 100%. Once the humidity goes above 100%, it turns into water, typically in the form of condensation on cool surfaces. 

Dirt Crawl Space  

Dirt crawl spaces are cheaper and easier to manufacture, which means they’re a popular option for many designers and manufacturers looking to save money. However, while they might be cheaper and easier for the initial building team, they’re much more frustrating to deal with as a homeowner because they’re prone to high levels of humidity. 

When you have a dirt crawl space, you’re not really going to be able to fix your humidity problems unless you lay down a durable water vapor barrier. That’s because even if you dry out the top level of the dirt, the earth will still be moist far down, which can rise into the crawl space and cause plenty of issues with high humidity. 

Lots of Rain  

Have you recently had issues with rain in your area? If you have, it could be impacting your home’s ability to avoid leaks and water coming into your crawl space. Rain can increase the amount of hydrostatic pressure on your home’s foundation as it sinks into the ground, which can be difficult on your crawl space walls. 

Unfortunately, rain issues are common in many areas of the United States’ East Coast. The closer you live to the coastline, the more likely you are to have serious problems with rain. You need to be prepared for the ways in which rain problems can impact your home’s stability, and excess crawl space moisture is one of the ways it can do so. 

Flooding in the Area 

Rain can sometimes cause flooding, which can end up causing its own problems. Not only can floods sink into the ground, where they cause large amounts of hydrostatic pressure, but they can also cause large amounts of water to stand around a home. This can be terrible news if you have crawl space vents or windows that are ground level. 

Although flooding is a different problem than rainwater, it often comes along at the same time. This is especially the case if your area tends to have a “dry season” and then a “wet season.” The dry season will dry out the soil, making it less open to rainwater soaking into the ground, and the wet season will be more likely to cause floods.

The humidity level in your home may change depending on the area in which you live and the level of humidity you’re used to. However, the typical range of healthy and happy humidity levels is anywhere from 40-50%. This might change somewhat through the year as well; you might need to keep it below 40% in the winter to avoid condensation on the windows.

Lowering the humidity level in your home is easier said than done. A dehumidifier may be helpful if you have a lot of humidity and you’ve already done your best to mitigate it. It’s also important that you fix any lingering humidity issues in your crawl space, because that will migrate into the rest of the home.

You should try to keep your crawl space humidity between 30-60%, ideally around 50-55%. The ideal crawl space humidity may change slightly depending on where you live and whether you currently have moisture and condensation problems in your crawl space, however.

Typically, you’ll be able to set your dehumidifier to a specific percentage of humidity you’d like the air to stay at. It’s a good idea to set your dehumidifier to 55%. If you end up with excess condensation, you can lower it; if you feel like things are too dry, you can increase it.

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The Experts at JES Are Here to Help You

 If you’re not sure of the source of your foundation problem, give us a call at 757-301-4820, and schedule an inspection. We’ll find out the cause of the problem and help you find the perfect solution.

You can do a variety of tasks on your own, but at the end of the day, a full crawl space encapsulation has to fall to a crawl space repair expert. Instead of trying your hand at a DIY fix, you should seek out an expert to help if you have high indoor humidity or significant amounts of crawl space moisture, 

The best thing about requesting an inspection from a JES crawl space repair expert is that it’s free. You don’t have to pay up front for your inspection. You can ask to get some insight on your crawl space and learn more about what the problem is, then work together with a crawl space repair expert to construct a solution that will work for your home’s unique position.

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