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Crawl Space Ventilation

Crawl Space Ventilation

In the past it was common practice to endorse crawl space ventilation. The idea behind this practice was that venting the crawl space would keep it dry. We now know that this just isn't the case.

Crawl space ventilation, especially in humid areas, ends up doing more harm than good. The outside moisture that's pulled into the crawl space creates the ideal environment for mold, mildew, insect infestations and wood rot. All of which thrive in environments that have a relative humidity that's over 50%"Experimental studies have show that crawl space ventilation is usually counterproductive, especially in humid climates.". According to the USDA, "Experimental studies have show that crawl space ventilation is usually counterproductive, especially in humid climates."i

In fact, an Advanced Energy study found that crawl spaces with open vents stay above 70% relative humidity - well above the healthy humidity level of 50%ii. Even if a vapor barrier was installed, if there were open crawl space vents then high humidity continued to be a problem.

Why Is Crawl Space Ventilation Bad?

Crawl space ventilation typically results in high humidity which will:

Encourage mold and mildew to grow.

Create the ideal environment for termites and other pests.

Increase your heating and cooling bills.

Cause high indoor humidity, which will then invite dust mites in to stay.

You can see that crawl space ventilation can lead to some major problems. It's a good idea to protect your home, family and health by having a professional seal your crawl space. This is the only way to ensure that you won't have a crawl space moisture problem.

Additional Resources:

Crawl Space Moisture Control
Crawl Space Encapsulation Code



i. USDA. Techline: Crawl Space Ventilation. Retrieved from

ii. Advanced Energy. Housing Zone: Or Vent or Not to Vent. Retrieved from


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