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It's no secret that high humidity in crawl spaces can lead to mold, bacteria, and pests. Keeping the humidity at the right level is crucial to prevent these issues.
I'll show you how to understand and properly manage the humidity levels in your crawl space for optimal results.
Ideal crawl space humidity levels explained
The ideal crawl space humidity is 50-65%.
Your crawl space humidity levels will vary much more than other parts of your home, but keeping it around this level is ideal for preventing damp conditions, mold growth, and pests like termites from spreading into your home.
The ideal relative humidity of crawl spaces is higher than living spaces, which are recommended to be kept at 30-50%.
There are three main reasons for this:
- 1A crawlspace isn’t lived in, so you don’t have to worry about personal comfort.
- 2Crawl spaces are usually not used for storage, so you won’t have personal belongings to protect from damp conditions.
- 3If you lower the humidity levels too much, then you can experience shrinkage. This can damage the wood under your home, leading to creaky floorboards and cracked drywall.
It’s normal for crawlspace humidity to be higher than in interior rooms as it’s outside your living space.
However, that moisture in the air still needs to be regulated to keep your home safe and comfortable.
How to choose relative humidity based on goal
Goal | Below 40% | 40% - 50 % | Over 60% |
|---|---|---|---|
Best for total home comfort | |||
Ideal for allergy sufferers | |||
Manage asthma symptoms | |||
Avoid respiratory illnesses | |||
Stop the spread of viruses | |||
Negate static electricity | |||
Discourage bacteria and mold growth | |||
Fight dust mites | |||
Best for crawl space |
Related article: Recommended dehumidifiers for basement
Understanding dew point versus humidity
When considering the relative humidity in your crawl space, you must also consider the temperature and conditions you live in, as this influences the dew point.
The dew point is another measure of the moisture in the air and takes into account temperature too.
This is important when considering outside areas like crawl spaces which aren’t regulated.
Basically, warm air can hold much more moisture than cold air.
Therefore, if you have hot conditions with a lower relative humidity, it can actually be worse than cold conditions with a higher relative humidity.
This is because there’s a higher dew point, meaning you’ll feel more humid, and your crawlspace is more likely to suffer from damp conditions.
If you live in a hot climate, you should keep your crawl space humidity at 50-60%.
If you live in a colder climate, you can allow the humidity to go up to 60-65%.
What should crawl space dehumidifiers be set at?
Your crawl space dehumidifier should have a programmable humidity level and a humidistat to measure the humidity and turn the appliance on and off as needed.
You should keep your crawl space dehumidifier to between 50 and 65% humidity, depending on the temperature and environmental conditions.
This chart can help you identify what humidifier settings you should use based on the current temperature and outdoor relative humidity to achieve a crawl space RH of 50% to 65%.
Temperature (°F) | Outdoor RH (%) | Ideal Crawl Space RH (%) Setting |
|---|---|---|
50-60°F | 60-70% | 50-55% |
50-60°F | 70-80% | 50% |
50-60°F | 80-90% | 45-50% |
60-70°F | 60-70% | 50-55% |
60-70°F | 70-80% | 45-50% |
60-70°F | 80-90% | 40-45% |
70-80°F | 60-70% | 50-55% |
70-80°F | 70-80% | 45-50% |
70-80°F | 80-90% | 40-45% |
80-90°F | 60-70% | 50% |
80-90°F | 70-80% | 45-50% |
80-90°F | 80-90% | 40-45% |
Related article: Guide to dehumidifier settings
How long does it take to dehumidify a crawl space?
The first time you use a dehumidifier, it could take up to 12 hours for the dehumidifier to reduce the humidity to the desired level.
It all depends on the relative humidity of your crawl space and the capacity of your appliance to handle the moisture.
For example, standard dehumidifiers may be able to remove up to 70 or 80 pints of moisture per day, but dehumidifiers designed for flooding and water damage may be able to remove twice that amount per day.
Once you’ve removed the initial high humidity, your dehumidifier will just need to maintain the right humidity levels in the crawl space air.
This means it won’t have to work as hard, and it shouldn’t take as long.
However, you may need a crawl space dehumidifier set up permanently if you live in an area of very high humidity.
Specific crawl space dehumidification units with a built-in pump can be installed.
This allows them to operate continuously to maintain consistent humidity levels without manually emptying the tank.
Related article: Top-rated whole-house dehumidifiers I recommend
Reasons your crawl space is too humid
Stagnant water in the crawl space
This can be caused by rain or crawl space flooding and is typical after a storm, or it can be caused by a drainage issue or plumbing leak.
Stagnant water can wreak havoc underneath your home, particularly on any exposed wood.
This can lead to increased wood moisture levels, wood rot fungus, and even damage to hardwood floors.
You can combat the humidity or install a vapor barrier.
Still, it’s crucial to determine the cause of the stagnant water and resolve the underlying issue wherever possible to reduce crawl space moisture levels.
Ground moisture evaporation
The ground beneath your home is full of water, which can also add to the crawl space humidity level.
The soil itself can seem dry, but it’s because the moisture is actually evaporating up into the damp crawl space.
This is a very common issue in high-temperature areas where there is more evaporation and less cool air.
It’s hazardous because it can increase wood moisture levels and negatively impact the structural integrity of your home.
Many people install a crawl space vapor barrier to prevent ground moisture evaporation.
Outdoor air entering through the space vents
Crawl space vents are designed to let air in and improve ventilation for a healthy crawl space, but they can actually cause humidity problems.
As the cooler air enters through the crawl space vents and comes into contact with the high crawl space humidity, it causes the water to be released from the air.
This creates condensation and can lead to standing water gathering in the crawl space.
Exposed dirt crawl space floor
An exposed dirt floor and soil in your crawl space can make controlling humidity levels much more challenging.
A dirt floor provides the ideal surface for capturing and absorbing moisture from the hot air, thereby increasing the humidity level.
The dirt won’t just cause moisture problems either, as it can lead to fungal growth and cause bacteria to spread.
This can result in poor indoor air quality throughout your home.
ACLAB Note:
A dehumidifier does not clean the air. It does prevent certain microbes and bacteria from thriving by removing moisture, but it does not purify the air. In order to clean the air you may need an air purifier.
Related article: Best rated dehumidifiers and air purifier combos
What happens if humidity is too high?
Promotes mold growth
The high moisture content and humid air lets the mold thrive and spread quickly, and it can even travel up into your home.
This can impact your health and present dangers or issues of concern for most people with pre-existing allergies or respiratory conditions.
Leads to wood rot
Wood floors and beams can become severely damaged when exposed to air with a high moisture content for a long period.
The wood moisture levels will increase as it absorbs the water vapor, and this can lead to wood rot.
High wood moisture levels in your crawlspace can damage the foundation underneath your home.
Dealing with it can be expensive and a real nightmare for homeowners. If you do think there are issues with your foundations, you should contact a professional.
Most of the time, they will provide a free inspection before you have to commit to any work.
Bugs and pests
If left unchecked, these termites and other critters can cause serious structural damage to your home’s foundation.
In the long run, this can be a serious problem, and the damage to the floor and walls of your house can be much more expensive to fix than just solving the humidity issues in the first place.
How to reduce crawl space humidity
Crawl space encapsulation
The main reason your crawl space can get so damp is that it’s not sealed off or protected from the elements.
Crawl space encapsulation creates a first line of defense against high humidity levels with a thin impermeable sheet of polyethylene lining the floors and walls.
The encapsulated crawl space prevents stagnant water from gathering through condensation and prevents evaporation from the soil upwards.
Installation can take some time, but having a sealed crawl space is the leading way to reduce water problems, and it can even increase the energy efficiency of your home.
Sump pump to pump the water out
Once installed, a sump pump will pump water out of your crawlspace and safely away from the foundation of your home.
Installing it in the lowest part of your home allows the water to flow into a bucket.
Once it reaches a certain level, the pump will automatically activate and the process will remove the moisture.
This is one of the solutions which can remove a lot of water quickly, but you will need to deal with the issues causing the moisture build-up too.
Crawl space dehumidifiers
If you’ve noticed high humidity in your crawl space, then it’s worth investing in a crawl space dehumidifier.
This appliance will regulate the air and actively remove moisture using a dehumidification process where it will heat and cool the air.
If you have a very wet crawl space, you can also connect it to your plumbing or a sump pump, so it actively drains without having to be emptied.
ACLAB Note:
Regular dehumidifiers are most effective in summer and can struggle in winter because the low temperatures can freeze the dehumidifier coils.
Dehumidifiers for crawl spaces are usually built for year-round use, so you can use them in summer or winter conditions.
Invest in a vapor barrier
A vapor barrier is similar to encapsulation but only involves lining the floor of your crawl space with impermeable material.
It’s considered the minimum moisture defense you should use in this part of your home as it prevents water evaporation upwards.
It can also reduce the risk of flooding from rainwater. If you live in an area with heavy rainfall, then a vapor barrier is extremely useful.
However, as the vapor barrier only lines the floor, it won’t be as effective as crawl space encapsulation.
FAQs
Can my crawl space be too dry?
Yes, a crawl space can be too dry, which may cause wood to crack or shrink.
Should I put a fan in my crawl space?
Installing an effective exhaust fan as an air conditioning system can help to remove wet air and stop humidity from circulating around your crawl space.
Just make sure the fan circulates and vents your hot air out without letting cold air in, as this can lead to condensation, which will cause your humidity levels to rise.
Should you open vents in the crawl space?
Only open crawl space vents in dry weather; keeping them closed in humid or cold conditions helps prevent moisture and mold.
What should not be stored in a crawl space?
Papers, books, photos, and electronics should never be stored in a crawl space because the humidity levels can cause damage.
