For many years, it was believed that crawl spaces needed to be vented. The theory, then, was that vents installed at the foundation between the exterior and crawl space provided benefits such as allowing air exchange, and enabling fresh air to come in while stagnant air moved out.
However, it turns out these vents actually caused more harm than good by inviting warm, moisture laden air in from the outside and through the foundation, and creating a breeding ground for mold, mildew, and pests. Thanks to independent third-party research on the topic, now we know that the best way to prevent moisture in your crawl space is to seal air pathways and install a high-quality crawl space liner.
Scientific Reasons to Cover or Remove Crawl Space Vents
If your existing home has crawl space vents, consider covering them. If you’re building a new home and you’re on the fence about whether or not you should include vents, don’t. Warm air is never totally without moisture, no matter which climate of the US you live in. Nature is constantly trying to reach equilibrium, thereby introducing the two culprits of vapor drive: temperature differential and humidity differential. Here’s how it works:
1. Temperature Differentials
With a national average soil temperature of 55 degrees Fahrenheit, your crawl space would naturally stay pretty cool. In the warm summer months, as temperatures climb outside your home, that warm air is going to try to reach a balance with the cooler temperature of your crawl space. As this happens, the warm air outside is naturally driven into your crawl space and vice versa.
2. Humidity Differentials
As the warm air outside is exchanging with the cooler air of your crawl space, so too is the humidity. Lower humidity likely to be found in your crawl space is exchanging with higher humidity outside (depending on the geographic area, time of year, and even time of day). Point is, you want to eliminate the opportunity for moisture laden air to be driven into your crawl space.
The Benefits You'll Experience From Being Vent-Free
After you’ve had the opportunity to cover or remove your crawl space vents, it will be important to take the ground in your crawl space out of play. The ground is another source of moisture that will constantly be trying to reach equilibrium with the space above it. You can do so by encapsulating with a quality crawl space liner material. Here are the benefits you should start to notice almost immediately:
Lower Humidity in the Crawl Space.
This should result in better indoor air quality – less mildew, mold, and associated odors.
Without air temperatures competing, you should see a leveling of the temperatures in your crawl space and that should result in better energy efficiency from your HVAC system.
Modern technology and new scientific study results have rendered vented crawl spaces obsolete. If your goal is to improve the comfort, air quality, and energy consumption of your home, you should consider covering your vents and fully enclosing and conditioning your crawl space with a quality liner.
Bryce Skeeters is the StegoCrawl® Product Lead Manager at Stego Industries, LLC. He has been a part of the Stego team for nearly ten years, after transitioning from a real estate career in home renovations. In addition, he was part of the team that developed StegoCrawl Wrap. Bryce enjoys working as a trusted consultant to architects, engineers, and contractors to further their understanding of concrete moisture management, and to ensure the highest quality in both residential and commercial projects.