What Is The Ideal Humidity For A Crawl Space? 

Sometimes the less-seen portions of the house are among the most important. The crawl space might not be a regular part of your living space but for buildings that have it, it is an important portion of the home. Knowing the humidity level anywhere in your home is important, but even more essential for the poorly ventilated, rarely used spaces like attic, basement and crawl spaces. However, for those who are in concern to know what is the ideal humidity for crawl space, this article is here to inform you.

What is the ideal humidity for a crawl space?

What is crawl space?

A crawl space is basically a hollow area usually found underneath a house just between the first floor of the building and the ground. In some buildings, the crawl space is actually above the house just beneath the roof. In either case, the crawl space is such a limited space that it is impossible to stand up inside it. One has to crawl to gain access hence the name. It measures roughly 1 to 2 feet in height.

The main purpose of a crawl space is to elevate the house off the ground. It also serves as space for cool air to circulate into the house. Additionally, the hollow space is where many of the important fixtures in the home like plumbing, ductwork, heating, and electric wiring passes. Some homeowners also use it as a sort of basement where items that are not frequently put to use are stored. Despite its importance, crawl spaces are prone to dampness which is one of the problems you might have to deal with if your home has a crawl space. But why is this so?

Why Your Is Crawling Space Always Damp?  

Moisture from the ground: one of the most common causes of dampness in a crawl space is the evaporation of moisture from the ground. Since your crawl space is in direct contact with the ground, evaporated moisture is trapped within the hollow space and this can cause dampness. It will even be a bigger problem in areas where the water table is close to the surface.

Outdoor air: when outdoor air gets into your crawlspace, it becomes cooler. Since cool air holds less moisture compared to warm air, the relative humidity of the air in the crawl space will become a lot higher than it was outside thus causing dampness.

Plumbing issues: sometimes a damp crawl space isn’t as a result of natural causes. Leaking pipes can cause pools of water to form in your crawl space and this will inevitably cause dampness within the space.

Although having a humid crawl space is not ideal, it is almost impossible to have a completely dry crawl space. How do we tell when the level of humidity in the crawl space is too high? We need to know the ideal humidity level of a crawl space

What Level Of Humidity Is Ideal For Crawl Space?

To prevent structural damage, threats to health and other consequences of high humidity in crawl spaces, it is important that you keep an eye the humidity of your crawl spaces. But what level of humidity is ideal for your crawl space? To answer the question you need to understand why you need to keep humidity levels low in your crawl space in the first place.

Molds and mildew thrive in high humidity environment. Generally, they need a minimum relative humidity of 70% for growth and development. However, even this number can change considerably based on several factors. Some molds grow under humidity conditions less than 70%. Based on this figure, it is recommended that you keep humidity levels in your crawl space around or below 50%.

Effects of High Humidity in Crawl Space

The stack effect: according to experts, up to 50% of air within the home can come from the crawl space. This is due to a phenomenon known as the stack effect. If the humidity level of your crawl space is high, the damp air from the crawl space will get into your home this leads will affect the quality of air within your home leading to some debilitating effects.

Strange smells: when damp, humid smell escapes from your crawl space into your home it can leave an unpleasant musty smell in your living space that will be quite uncomfortable.

Allergens: a humid crawl space is an ideal breeding ground for mold, mildew and other types of allergens. This gets into the home and can cause serious allergies especially for anyone prone to allergic reactions in your home.

High humidity: A highly humid crawl space can cause a spike in the humidity level within your home as well. Since humid air from the crawl space will eventually end up within the house itself, it can cause high humidity in the home leading to discomfort and other resultant effects of high humidity.  

Compromised structural integrity:  Since the crawl space is right at the foundation of your home, high humidity can weaken your entire structure. Growth of mold and mildew on walls and floors will eventually lead to weakness and cracks that may get worse with time.  

How to Get Rid Of Moisture in Crawl Space

Install a Vapor barrier: as the name implies a vapor barrier is a form of barrier you can install in your crawl space to prevent water vapor from getting into it. Since a crawl space is typically in direct contact with the ground, one of the surest ways of reducing how much moisture gets into it is to cover the ground up with vapor barrier. This prevents moisture from getting into the air and saturating it. With a vapor barrier in place, you are one step towards having a crawl space with normal humidity level.

Seal up the vents and install a whisper fan: as mentioned another possible cause of high humidity level in the crawl space is the warm air that enters into it from outside. One simple solution for this is to seal up space vents that bring air into the crawl space. You can do this using a sealing form board cut to the exact size of your space vent. Typically, it is advisable to still leave one vent open for ventilation.  For this vent, you should install a whisper fan which blows air out through the vent.

Install a dehumidifier: if your budget allows it, you can install a dehumidifier in your crawl space. This device reduces humidity levels in the air by removing excess moisture. Damp air in your crawl space is taken into the dehumidifier and water is removed from it either by cooling, adsorption or absorption. The now dry air is reintroduced back into the room after it must have been slightly warmed up within the dehumidifier.

Installing a dehumidifier unit in your crawl space is the perfect solution for getting rid of moisture in your crawl space and keeping the humidity level in check. The unit can be installed alone or in addition to the other solutions mentioned for effectiveness.


The crawl space might seem like an insignificant area but keeping the humidity level within it under check is important. It has a tremendous impact on the overall air quality in your home and the resultant health of every occupant of the house. That’s not to mention the effect of high humidity of the house itself. Thus it is important that you monitor humidity levels in your crawl spaces and keep it at an ideal level all year round.

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