What Should Crawl Space Humidity Be Ideally?

Having a crawl space in the house, you’d know about its acceptable moisture level. Excessive humidity, as well as insufficient humidification of this unoccupied, unfinished, narrow space between the basement and the first floor, leads to certain problems.

If you’d like to know the ideal crawl space humidity, troubles followed after the inappropriate moisture level, and solutions to solve them, go on reading.

what should crawl space humidity be
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What is acceptable moisture level in crawl space?

Since prolonged inappropriate humidity will have unpleasant consequences, purchase a digital thermo-hygrometer to monitor the relative humidity levels.

Ideal crawl space humidity levels vary from 40-65%. This is the best level to keep the air healthy in the house.

As not less than 40% of crawl space air gets into the house which influences the breathing quality of the air in the house and yearly energy savings.

If the humidity is above 65%, it’s time to take measures and reduce the crawl space moisture levels to avoid moisture problems like mold growth, fungal growth, and wood rot.

If the humidity of crawl spaces is below 40%, you’ll also have issues connected with the wood shrinkage in the house.

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Why the crawl space is too humid?

Some occasions should be discussed as they influence the crawl space humidity levels. Once you determine the root of the high humidity, you can move on to solving it.

Moisture evaporation. Typical dirt floor crawl space and foundation walls of porous concrete absorb and evaporate water in the air. Thus, humidity can be increased.

Bulk water. This problem can occur after heavy rain when a puddle of standing water appears on the floor. Most likely, this is due to poor drainage. Check whether the slope of the ground goes away from your house or vice versa toward the house. In this case, you need to correct the situation and change the direction of the soil slope.

Also check whether the water supply system is leaking, especially if it is already old and the pipes haven’t been changed for a long time.

Outside air. Directly the crawl space vents air from the outside moves in the room. It doesn’t matter whether it is cold or hot air.

Cold humid air falling into the crawl space is absorbed and deposited on the dirt floor or concrete walls causing excessive crawl space moisture.

The hot air that moves in the crawl space vents on hot days condenses on the cool walls and floor which also increases the humidity level.

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Consequences Of Continuous Moisture In Your Crawl Space

If the crawl space humidity stays high for a long time, you’ll have only negative effects.

First of all, this is the appearance of musty odors in your home. If you felt the musty smell and you cannot give an explanation for its appearance, then most likely it is connected to the prolonged moisture levels.

As moldy crawl space air gets into your home, you smell that unpleasant odor.

The appearance of mold is another negative effect. Mold growth or fungal growth is possible at a relative humidity of 70%. This is a critical moisture level that should be corrected immediately. After all, mold is very dangerous and can cause breathing problems.

Standing water in your home’s crawl space causes insect infestations like different bugs and sewer flies. So, if you don’t do something with your plumbing leak and don’t fix the drainage system, you’ll likely have puddles with insects.

Moreover, constant high humidity in your crawl space will bring water damage to the wooden structures. Wood rot is inevitable if you don’t struggle with high levels of moisture. Rotten wooden beams and a deformed wooden floor will need crawl space repairs. In addition, you can face more substantial issues related to the destruction of the structural integrity of the home foundation.

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How To Lower Crawl Space Humidity Levels?

If your crawl space has an increased level of humidity, the first thing you need to do is determine its cause. Once you’ve determined the cause of the humidity, there are steps you can take to correct the problem.

Read all the possible options for solving problems related to the high crawl space humidity and apply the most suitable one for your situation.

Crawl space dehumidifiers

Dehumidifier is an air conditioning device designed to decrease the amount of moisture in the air and maintain relative humidity at a certain level. A crawl space dehumidifier must be installed only in the encapsulated crawl space. A dehumidifier fan circulates the dry air all around the crawl space area and lowers the crawl space humidity level.

Dehumidifiers withdraw moisture in the air and raise indoor air quality which is very important for people with breathing problems.

You can choose a dehumidifier of any quality after carefully evaluating them by their performance, efficiency, ease of use, and noise level.

Warning: a dehumidifier will be useful and do a good job of decreasing crawl space humidity levels if it’s fixed in a sealed crawl space. If the room is ventilated, then the dehumidifier will not cope with this task and you will simply dry the outside air.

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Crawl space encapsulation

Crawl space encapsulation is a method of covering the floor, walls, and sometimes ceiling perimeter of your crawl space with heavy-duty polyethylene. Thus, you create a vapor barrier in the room that helps to keep humidity levels at a minimum rate.

The vapor barrier is a great option that prevents evaporation, absorbs excess moisture, and can last for up to 50 years.

The polyethylene coating for vapor barriers is made of high-strength material up to 20 mm thick, which creates a vapor barrier for moisture to enter the crawl spaces. Therefore, sealing a crawl space eliminates humidity fluctuations because it stops moist air from settling in the room, forming condensation, that in turn averts mold, mildew, and wood rot.

If you construct crawl space sealing, you’ll breathe healthier indoor air and enjoy living in an energy-saving home.

Sump pump

A sump pump is an appliance placed in the crawl space to drain water from beneath your home that appears in the crawl spaces seeping through the dirt floor. It has a mechanism that detects elevating water levels and pressure to ensure that these levels do not rise too high.

Thus, a sump pump protects your home from flooding by moving water from one location to another.

A sump pump dries your crawl space during floodings or plumbing leaks and effectively regulates the crawl space humidity level.

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Is 60% humidity OK for crawlspace?

60% is an acceptable humidity level for a crawl space. But watch more carefully so that the moisture content does not become greater.

Is 65 humidity OK in crawl space?

65% is already increased moisture level. Do something to lower moisture or you’ll be dealing with moisture problems soon.

Is 70% humidity too high for crawl space?

If the humidity level stays 70% and more for a long time, then more likely you already have humidity problems that are detrimental to the health and home structures. Don’t put off solving this problem until tomorrow. Act today!


So, it’s very important to monitor and maintain your crawl space humidity level at an acceptable rate to avoid problems in the future. Purchase a hygrometer and control humidity, take care of the vapor barrier in advance, constantly check the water drainage system, and timely repair outdated water pipes.

If you already noticed a high moisture level, then it’s time to act immediately to lower it. High-quality vapor barrier, dehumidifier, or sump pumps will help you to cope with the task.

James Derrick

If you have become a reader of my blog, you are thinking about how to properly equip your home. I want to say that together with my family we live in our own big house.

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