Can A Crawl Space Be Too Dry?

Most crawl spaces tend to have higher relative humidity levels than the rest of the home. However, you may be wondering if a crawl space can be too dry. We researched the topic, and this is what we discovered.

A crawl space can be too dry if the relative humidity falls below 30%. At this humidity level, wood may begin to shrink, causing structural damage.

Keep reading as we will discuss the ideal humidity level for a crawl space, how you can get rid of moisture in a crawl space and whether you should put a dehumidifier in a crawl space.

closed cell spray foam insulation in basement crawl space, Can A Crawl Space Be Too Dry?

How dry is too dry for a crawl space?

It is advisable to maintain relative humidity in a crawl space at 30% to 50% to enhance the structural integrity of a crawl space. If the crawl space is too moist, you will encounter various challenges such as wood rot, and mold and mildew build-up. On the other hand, the wood shrinks if the crawl space is too dry.

A crawl space can be excessively dry if the relative humidity falls below 30%. Low relative humidity levels affect the structural integrity of your home and affect the health of the residents in the house.

When relative humidity is too low, eyes become dehydrated and irritated, the skin becomes brittle and inflamed, and the mucous membrane lining the respiratory tract dries out.

The crawl space is likely to be too dry during harsh winter if it is open vented. Cold air holds less moisture. As the cold air circulates the warm crawl space, it expands and siphons vapor from the crawl space, lowering the relative humidity level.

Therefore, it is advisable to regulate how much cold air is allowed into a crawl space to avoid reducing the relative humidity below ideal levels.

It is advisable to install a thermo-hygrometer in a crawl space to monitor relative humidity, thus ensuring that it doesn't become too dry. It would be best if you opted for a digital hygrometer that alerts you as soon as the relative humidity falls below a pre-set level.

This smart thermometer hygrometer enables you to monitor temperature and humidity levels in real-time from anywhere. Check it out on Amazon.

How do I get rid of moisture in a crawl space?

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Crawl spaces are susceptible to higher humidity levels than the rest of the house since water vapor naturally rises from the exposed soil and becomes trapped in the enclosed crawl space. The moisture provides a favorable breeding ground for molds and causes wooden structures to rot.

Additionally, it significantly increases your energy bills through the use of ACs and dehumidifiers in a bid to control the moisture level.

Sources of moisture in a crawl space

To adequately address moisture problems in your crawl space, you need to understand the source of this moisture. The primary vapor sources in the crawl space are humidity, damp ground, and groundwater.


Warm air rises because there are more spaces between its molecules, making it less dense than the surrounding matter. As the air rises, it carries more moisture molecules due to the higher energy levels of the water particles. Therefore, the moisture levels in the crawl space rise.

Damp Ground

Damp air discharges vapor into the air in your crawl space. Over time, this vapor may accumulate, leading to elevated moisture levels.


Improper grading, drainage issues, or broken water lines may result in excess water in your crawl space. If the crawl space encounters any of these challenges, it may be impossible to address the humidity problem unless you begin by addressing these issues.

Tactics to control moisture in a crawl space

Crawlspace under a residential building with new vapor barrier, Is Crawl Space Encapsulation A Good Idea - The Pros And ConsCrawlspace under a residential building with new vapor barrier, Is Crawl Space Encapsulation A Good Idea - The Pros And Cons

Use a dehumidifier

It is advisable to use a dehumidifier to regulate the humidity level in a crawl space whose problematic source of moisture is humidity. Read on as we will elaborate on this later.

Install a vapour barrier

Although you cannot rid the crawl space of the damp soil beneath the crawl space's floor, you can address moisture problems arising from damp ground by installing a vapor barrier.

The thickness of the vapor barrier you use will determine how effectively it will control moisture levels in your crawl space. Additionally, you should consider the type of floor you have in the crawl space because different floors require different dehumidifiers.

Moreover, since the moisture content in the soil varies from region to region, opt for a moisture barrier that is ideal for your crawl space's moisture content.

You may also consider permeance requirements and pre-existing moisture problems when settling for a moisture barrier. Permeance measures the rate at which water vapor moves permeates a material.

Install french drains

Installing French drains and sump pumps ensures that your crawl space has an adequate drainage system, ensuring it does not flood.

French drains are primarily used to drain groundwater from gardens and around building foundations. They are ideal where the soil is prone to flooding or saturation by rain.

Installing a French drain is not only labor-intensive but also time-consuming. It would be best to consider the soil slope to ensure that the french drain works efficiently. It is advisable that the bottom of the drain slopes about one inch for every eight feet in the direction you intend to drain the water.

These drains should be designed for long-term use as they are not as effective in removing moisture from over-saturated soil in a short time. You may direct the water to a dry well, a low-lying area in your property away from the crawl space, or even a drainage ditch.

Encapsulate the crawl space

Crawl space encapsulation is where you seal the crawl space to have complete control of the moisture content. As such, you install a vapor barrier to the crawl space floor, close the foundation vents, and insulate the wall.

Encapsulation requires that the crawl space is first sealed completely then a dehumidifier is used to regulate moisture levels. Encapsulation will not work if gaps allow outdoor air to seep into the area.

It is advisable to use encapsulation alongside installing french drains. This is crucial since although encapsulation allows you to control the humidity levels in an enclosed space, it does not address flooding and groundwater issues.

Should you put a dehumidifier in a crawl space?

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It is advisable to put a dehumidifier in a crawl space to reduce the relative humidity in the crawl space while improving the indoor air quality in the crawl space.

Installing a dehumidifier in a crawl space will derive the following benefits:

Health benefits

Most of the air you inhale in the home comes from spaces such as crawl spaces. Thus, if the air rising from the crawl space is contaminated by molds and other impurities, you will suffer from respiratory complications and allergies.

Because a dehumidifier lowers the relative humidity in a cellar, it hinders mold increment and improves indoor air quality, reducing health complications and allergies.

Preserves the structural integrity of your home

A dehumidifier will aid in keeping your home free of rot that may arise due to high humidity levels in the crawl space.

It makes your home more energy-efficient

It is more eco-friendly to use a dehumidifier to rid your crawl space of excess moisture instead of turning on the AC. Moreover, the dehumidifier reduces the stress on your AC and also enables you to lower the thermostat.

Improves the comfort of your home

High humidity levels can cause condensation on the ceiling of a crawl space which may cause the floor in your home to be very cold. Moreover, high humidity can also make you and members of your household feel hot and sticky.

We mentioned earlier that warm air rises. Therefore, addressing the moisture problem in your crawl space will make your home more habitable.

This dehumidifier has four multi-functional modes to choose from based on the expected effect. It is ideal for use in spaces covering a floor area of 4,500 square feet. Check it out on Amazon.

It is advisable to ensure that the crawl space is free of leaks and water puddles before installing a dehumidifier as it will not resolve these shortcomings. It is also crucial to address any mold problems before running a dehumidifier.

In conclusion

A tight crawlspace under a house

Maintaining an ideal relative humidity of 30% to 50% is advisable to keep your home comfortable and moisture-free. If relative humidity falls below 30%, the crawl space can be too dry.

At this low relative humidity level, wood in the crawl space will shrink. However, the wood in the crawl space will begin to rot if the relative humidity is too high.

You may also be interested in these articles:

Can You Convert A Crawl Space Into A Basement?

When To Run A Dehumidifier In The Basement? [And How Often]

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