Should I Leave the Crawl Space Door Open to Control Humidity?

Do you leave your crawl space door open to control humidity? Does that work? Many homeowners leave the vents of the crawl space open. So, it may make sense to leave the crawl space door open to dry out the crawl space. What are the potential negatives of an open crawl space door?

Will an Open Crawl Space Door Help Control Moisture?

If you live in an area where humidity is high, leaving the crawl space door open will only allow more humidity to enter the crawl space. Many homeowners are still convinced that a vented crawl space will stay dry. Therefore, the investment in crawl space encapsulation is not needed.

Would You Leave Your Front Door Open to Lower Humidity?

Imagine you are running your air conditioning and the humidity in your home is around 55%. The humidity outside is 70%. Then you decide to open your front door to help lower the humidity in your home because you want it at 45%. As you can imagine, what will happen is the 70% humidity will rush in to bring the 55% relative humidity to 70%. Wet air chases dry air and the relative humidity wants to reach equilibrium.

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What Time of Day is Humidity the Lowest?

The only way an open crawl space door will lower humidity is the humidity in the crawl space must be higher than outside humidity. For many homes, this is actually happening at certain times of the day. Most outside humidity is higher at midnight to early morning. As the sun comes out it starts to lower the humidity.

According to the National Institute of Water and Atmospheric Research, the humidity is lowest at 2pm but starts to increase rapidly all the way to midnight. So if you are going to leave your crawl space door open to control humidity, it is best to do it between 2pm and 3pm if your humidity is higher inside than outside.

Leaving the Crawl Space Door Open is Not Recommended to Control Humidity

Since most of the homes we inspect and work on have high moisture problems in the crawl space, we instruct homeowners to not only keep the crawl space door closed but to air seal and insulate it.

Remember, there are more issues than high humidity that can come from leaving the door open. Cats, bugs, skunks, snakes, and other critters would love to bask in your dark cool crawl space during the hot part of the day. They can destroy your insulation, vapor barrier, and ductwork pretty easily.

Another issue is if it begins to rain or becomes foggy, the humidity is at 100% and can enter the crawl space. Plus, a blowing rain or flash flood can cause the crawl space to take on lots of water and flood.

You May Want to Lock Your Crawl Space Door

According to, crawl spaces are great ways for thieves to enter your home unnoticed. In this news report, homes in South Carolina are among the top 10 states with the most break-ins per 100,000 residents. This increase in burglaries is fueled by many homes in South Carolina built on crawl spaces.

We personally have found squatters living in crawl spaces and had to call local law enforcement to have them removed. Imagine the horror of our customers finding out they had someone unknowingly living in their crawl space. Make sure you not only keep your crawl space door closed but also locked and perhaps include it with your alarm system.

What Next?

Do you need help with crawl space encapsulation in Alabama, Georgia, Delaware, North Carolina, Tennessee, Kentucky, or South Carolina? If so, please contact us to schedule your assessment. Also, let us know in the comments below if you’d like to suggest a future blog post.

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