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Should I Open or Close My Crawl Space Vents in the Summer?

Crawl space vent open.

For decades, the conventional wisdom held that ventilating a crawl space in the summer with open vents was beneficial, promoting air circulation to keep the area dry and prevent moisture buildup. This practice was rooted in the belief that allowing outside air to flow freely underneath the house would help maintain a healthy foundation and interior environment.

However, as building science has advanced, we’ve learned that this traditional approach might not be as effective as once thought. In fact, research has shown that open crawl space vents can often do more harm than good, especially in areas with high humidity, leading to moisture problems, mold growth, and compromised air quality inside the home.

This article delves into the shift from open to closed crawl space vents, exploring the reasons behind this change and how it impacts homeowners today.

What Do Local Codes Say About Crawl Space Vents? 

Installing crawl space vent sealing.

Initially, building codes suggest that leaving crawl space vents open can be beneficial, yet they also permit closing them, offering homeowners and builders the flexibility to choose between an encapsulated or an open vent system.

Regardless of the choice, specific conditions must be met to comply with these codes.

However, we firmly advocate for closing the vents year-round, as it is challenging to regulate summer humidity levels in an open crawl space, leading to potential moisture-related issues.

Are Crawl Space Vents Effective? 

Imagine you’re living in a home, where the outside temperatures can hit 90 degrees. You have your HVAC running and it’s brought down the internal temperature to 65 degrees. Then you open the windows and warmer air rushes in. What happens? Warmer air will instigate condensation while raising the internal temperatures. That’s exactly what happens you have a vented crawl space. 

Although crawl space vents are mandatory in many areas and the intention behind them good, the logic behind vented crawl spaces is faulty. In fact, venting does the exact opposite. Your home would be safer and healthier if you cover the vents

Sealing and controlling ventilation is the way to go. With this approach, you’re still ventilating but controlling the humidity with a dehumidifier

What Are The Disadvantages of an Open Crawl Space? 

Untreated crawl space.

Various studies have shown that ventilated crawl spaces do more harm than good to your home. Vents let in excess moisture during humid and wet weather conditions. And this can raise humidity levels and foster various problems. Even if you install vapor barriers, they won’t keep the crawl space dry enough to stop mold growth. 

Your biggest worry should be condensation, a phenomenon that occurs when warm outside air comes into contact with cooler crawl space air. Condensation can trigger mold growth, which can range from light spotting to heavy staining as well as wood rot, decay, and rust. Over time, condensation can cause water puddles to form on the crawl space floor. 

The passive intrusion of humid air via vents can also contribute to a weaker support structure. Decaying and rotting wood won’t be able to support the home above. This can lead to potentially expensive repairs. 

More than 50% of the indoor air comes from the crawl space. A crawl space measuring 1,000 square feet can produce up to 10 gallons of moisture in a day, rising into your home and causing a number of issues besides forcing your HVAC to work even harder. 

Another concern is that venting can affect the quality of indoor air in the home. Upward moving air can carry with it mold spores, dust, pollutants, and allergens. All these can make the indoor air unbreathable. Anyone with breathing problems like asthma will be affected greatly. And that could mean more hospital visits and coughing. 

Not only does outside air bump up moisture levels, but it also increases home heating costs. Upward moving air creates a stack effect. You’ll find yourself running the air conditioner for longer to harmonize the conditions in your living space and the crawl space. 

Conclusion: Get Your Crawl Space Vents Closed ASAP!

Finished, encapsulated crawl space.

U.S. homes with closed crawl spaces outperform their vented crawl counterparts with regards to structural health, air quality, mold-resistance, and energy efficiency. Closed crawl spaces stay significantly drier than the wall vented crawl spaces with relative humidity levels staying below 60% for most of the hot and humid summer months. 

Want to keep crawl space moisture in check and create a healthy space? Seal all the vents and condition your crawl space. JES Foundation Repair professionals are experts in crawl space encapsulation and dehumidification. They can suggest a long-term and effective solution to control crawl space moisture while providing fresh air exchange.

Kick start your project with a free crawl space inspection and quote

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