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High Crawl Space Humidity

High humidity in your crawl space is a warning of hidden damage and issues, and, as such, should not be ignored. Here’s how you can spot this issue.

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There are many reasons why your property’s crawl space can be considered the most vulnerable area of your home. From its proximity to the ground, its relatively exposed nature, and the direct connection it has to your property’s foundation, your crawl space is often the first place to show signs of damage and deterioration. High relative humidity is just one example of the many problem signs that can show when a crawl space is in danger. 

Learning to spot these warning signs and act accordingly is a crucial skill for homeowners. In fact, it is vital to ensuring that your property’s crawl space, and its wider structure, is protected from avoidable damage. Allowing dampness and humidity to go on unchecked can cause serious issues. Of course, there are steps you can take to protect your Birmingham, AL home from these problems in the long-run. 

What Humidity Can Signify in Your Crawl Space 

High levels of relative humidity inside your property’s crawl space can be indicative of a few issues that you should not overlook. These include, but are not limited to: 

Leaking Pipes 

Serious leaks and plumbing floods are hard to ignore because of the sheer volume of water that is put out. While this can cause long term issues with dampness, this is less common because people tend to react quickly to plumbing floods. 

A minor leak, however, can be very hard to identify and will generally be more prolonged in nature. As such, the likelihood of them causing a long-term increase in humidity (along with all the issues that usually come with this) is much higher. 

rotted crawl space

Foundation Damage 

Damage to a property’s foundation is a fundamental problem, and, while it can lead to spikes in humidity, it generally will be the latter of the problems. Foundation issues like settlement and subsidence tend to start in the soil under a home and can cause widespread issues like fragmentation, cracking, and sinking, as well as dampness, water damage, and generally high levels of humidity in a property. 

If you notice spreading cracks in your home or find that some parts of your flooring are uneven, then it could be time to consider the possibility that there is foundation damage in your home. 

The Stack Effect 

The stack effect is a complex and subtle phenomenon that can impact your home in many ways. If you have crawl space ventilation that relies on allowing exterior air to flow into your home, then the stack effect (sometimes called the chimney effect) will be at work in your home. This process is notorious for causing elevated levels of humidity and condensation because of how it causes air to constantly enter and leave a home. 

This is why homes facing the stack effect may struggle with crawl space condensation during the summer months. As your HVAC system works to cool the air in your home, the stack effect will pull warm, humid air in from outside. The change in temperature will cause condensation and, eventually, dampness and humidity in your home. 

Malfunctioning Appliances 

If your dehumidifier or sump pump starts to work inefficiently, then you may find that high levels of crawl space humidity are one of the many different results. Alternatively, if your water heater or plumbing system experiences damage and deterioration, a leak can easily spring up. Even a small leak will contribute directly to increases in the relative humidity around your home. 

The most common culprits for this kind of low-level leak are water heaters and the joining points between pipes, or pipes and appliances. 

There are a few issues that high crawl space humidity could be a warning sign for. Some of the possible underlying issues can be very small, while others can be surprisingly big. Either way, crawl space humidity should not be ignored. 

Why Worry About Humidity and Dampness? 

Humidity and dampness in your Chattanooga, TN, crawl space may not seem like a huge deal. After all, your crawl space is a rarely traversed area of your home that can seem very removed from the rest of your property. Unfortunately, this is not the case; what happens in your crawl space will affect you and your home quickly. 

Health Implications 

Humidity can have several effects that will impact your health and wellbeing, as well as your comfort in the property. Crawl spaces that have prominent levels of relative humidity provide far more welcoming environments for fungal growth and pest infestations. 

High humidity will also make the likelihood of fluctuating temperatures rise quite dramatically. This can lead to several health-related issues, including a generally higher risk of cold & flu and the risk of serious side effects from prolonged exposure to mold, mildew, and other fungal substances. These risks are a little more serious and can include respiratory infections and even seizures. 

Other Problem Signs You Should Be Aware Of 

These are just some of the commonly co-occurring warning signs that you might find in a crawl space that also has high relative humidity. These issues can also indicate various other underlying issues in your property.  

Corrosion and Rust 

Corrosion and rust are some of the most common and easy to spot warning signs of persistent dampness and humidity in any space. Look at your pipes and appliances for discoloration, particularly orange staining, and changes to the texture and surface of pipes and metal. Corrosion and rust will generally cause flaking and bubbling across the surface in question, rather than clean cracks. 


Condensation on any surface is a sign of humidity, but some forms are far more common than others. For example, seeing condensation on your kitchen windows may be a sign of humidity, but it is not necessarily a sign of issues or damage in your home. Finding condensation on your crawl space walls and ceiling, however, is another matter entirely that should not be ignored under any circumstances. By the time you find condensation on your walls, you can be certain that the humidity in your crawl space has reached a critical point. 

Bad Odors 

Have you noticed a bad or musty odor in your crawl space that will not lessen even when you try to deep clean and air out your home? What about an unpleasant smell from your crawl space that is starting to spread through your home? Both are a sign that the high humidity in your crawl space is starting to affect the climate in your home as a whole. 

Mold and Mildew 

Mold and mildew are pretty much guaranteed results of dampness and humidity in a property’s crawl space. You will recognize mold and mildew as areas of discoloration with a slightly raised or fuzzy texture. These patches can be black, brown, white, gray, or even pink in color and should not be touched. 

Wood Rot 

Like mold, wood rot is a fungal growth. Unlike mold, however, wood rot is almost exclusively damaging to the structure of your home and should cause no direct health issues unless you ingest the spores. What wood rot will do, however, is undermine the stability of your property as a whole and lead to the decay and collapse of impacted wooden structures and surfaces. 

Sagging Floors 

Sagging flooring in your property is a strong sign of damage in a property. Your flooring should always be firm and stable when you walk on it. If you find that there is a slight bounciness underfoot, or you see visible unevenness and sagging in your floors, then this is a sign of joist, beam, or floorboard damage that should not be ignored. If you do not address the instability, then you could well end up facing a collapsing floor (which is far more worrying). 

Floor and Wall Gaps 

Gaps between your property’s flooring and walls are a sign that the structure of your home as a whole is moving and shifting. They are also a sign of immense pressure or a complete lack of support in key areas of your home. 

Cosmetic Damage 

High crawl space humidity and dampness can directly lead to cosmetic issues and damage like warped wood, flaking, staining, and spalling. These forms of damage may not impact the stability of your property, but they will impact its appearance and the value that you can expect it to have if you try to sell your home in the future. 

If you see any of these problem signs in your home, then it is time to call a professional as soon as possible. By acting quickly, you could save yourself a huge amount of time, money, and stress in the long-term. 

High Crawl Space Humidity


If your property has exposed crawl space vents, then you should make a point of contacting a professional to talk about your options and the benefits of covering your crawl space vents. Do not simply cover up your vents, however. 

The Stack Effect 

Crawl space vents were initially installed into properties because they were believed to be beneficial to the properties in which they were found. Between the 1950s and the 1990s, installing crawl space vents was considered best practice because it was believed to reduce dampness and humidity by increasing airflow. Of course, they were found to increase airflow because of the stack effect. This was later found to be harmful. 

The stack effect increases dampness and humidity while decreasing energy efficiency and temperature/climate stability in your home. There are many things that can feed into this, but open crawl space vents are the most influential and easy to fix sources of airflow in a home where the stack effect is present. As such, they should be your first point of consideration. 

Get Well-Fitting Vent Covers 

Getting durable, plastic vent covers that are heat-resistant, water-proof, and well-fitting will prevent or drastically reduce the stack effect in a property. Of course, the reduction of the stack effect is not the only benefit that you can expect to see from well-fitting vent covers being installed into your home’s crawl space. For a start, covering crawl space doors and vents is a key part of encapsulation and will prevent pests and water from getting into your home quite as easily. 

This, in turn, will influence the climate, energy efficiency, and heat retention that you can expect from your home by creating an environment that is separated from the outside world. This creates a kind of internal bubble that protects the climate of your whole home from outside influences in many ways.  

Waterproofing and encapsulating your property’s crawl space can go a long way towards protecting your home and interior climate from dampness and humidity. However, there are limitations to this process that you should be aware of. 

The Benefits 

Waterproofing is a highly beneficial process, especially when it is undertaken in conjunction with encapsulating activities like vent cover installation and vapor barrier fitting. The most obvious benefit, of course, is the way in which it cuts off the main body of your home from the dampness and humidity that an exposed crawl space can create. By distancing the rest of your home from the outside, waterproofing creates a healthier environment. 

This healthier environment is better for your home and for your family in many ways. This is true from preventing pest infestation, mold, and wood rot, to more subtle benefits like energy efficiency, increased comfort, and stable temperatures that make it easier to sleep and go about your day in comfort. Of course, this is dependent on the waterproofing being undertaken completely, but it also depends on the property being in the right shape for the process. 

The Limitations 

Like everything, there are limitations to waterproofing that you should keep in mind when thinking about undertaking the process of waterproofing and encapsulation in your crawl space. Primarily, waterproofing cannot be effectively undertaken in a home that has underlying damage to its structure or internal workings. While properties with damage that contribute to a generally damp atmosphere are most in need of waterproofing, they are the least suitable for the process. 

If you waterproof a fundamentally damaged property, then there are two main likely outcomes. First, there is a high chance that waterproofing will cover up the signs of serious structural damage like spreading cracks and fragmentation. This will allow issues to spread unchecked until they become impossible to ignore. Secondly, if the source of moisture is internal, you will create a water-tight environment that collects the moisture that is dropped into it. This will essentially incubate any spores that make their way in, too. 

While the process of waterproofing and encapsulation can seem quite simple and straightforward, we urge you not to try to undertake this work alone. DIY may seem like a smart way to save money, but the truth is, it can cause far more harm than good in the long-term. 

Don’t Try DIY 

The waterproofing process essentially has two main parts in the average home: preparation and waterproofing. In a healthy home, the preparation process is short and mostly about clearing away debris and blockages to make sure that the installation of all waterproofing measures can be undertaken swiftly. In a damaged home, however, it is far lengthier. 

This is where the key issues with DIY lie. Repairing underlying damage before waterproofing is fine when the damage is a loose pipe joint but a different matter when the damage is structural in nature. Foundation damage, bowing walls, and sagging flooring all require specialist tools and products to ensure proper and full repair. If you don’t have the right tools or skills, then you run the risk of causing more damage to your home or even causing injury to yourself and anyone who is helping you to deal with the issues in your home. 

Allow Professionals to Deal with Dampness 

One of the main benefits of hiring a professional to undertake waterproofing in your crawl space is the fact that they are able to deal with all underlying causes and co-occurring issues both quickly and safely. Not only do they have the training and skills but also the experience and all the right tools and equipment (tools and equipment that you would have to rent at great cost to do the work yourself). So, when professionals undertake your home’s waterproofing, you can be certain that the results will be quality. 

Let our team at AFS deal with your high humidity and waterproof your crawl space to the highest possible standard! We can promise you that the results won’t disappoint.  

Contact AFS Foundation & Waterproofing Specialists for Expert Encapsulation 

If you have seen signs of high crawl space humidity and you are concerned about the health and wellbeing of your home, then you should contact the team here at AFS Foundation & Waterproofing Specialists. We have been helping homeowners protect their properties from dampness, humidity, and the damage that they can cause across Birmingham, AL, Huntsville, AL, Mobile, AL, Nashville, TN, Chattanooga, TN, and Knoxville, TN. 

Before we start looking at how we can protect your home, however, we will arrange a free inspection appointment at a time and date that suits you, so that we can discover the current state of your home. If there is no pre-existing damage, then our team will likely suggest waterproofing an encapsulation. If there is damage, then that will need to be addressed first. Either way, our team will provide you with a written estimate for all costs associated with our suggested works. 


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