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Foundation Vents Helpful Or Harmful

Basement Authority of West Virginia provides facts and answers customer questions about foundation vents and crawl spaces.

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When I travel across the state for home shows and events, I often ask people if they have foundation vents on their homes. If I ask 100 people about foundation vents, I find that 99 of those homeowners use their vents in a way that probably wets their crawl space and encourages mold growth.

The conversation usually goes something like this:

“Do you have vents on your foundation?”


“When do you open them?

“I open them in the summer and close them in the winter.”

“And by doing this you are drying out your crawl space, right?”

“That’s right.”



“Have you thought about the science of crawl spaces?”

“No, I haven’t. I’ve been told that I need a certain number of vents for the square footage. When my home was built, it was built according to code.”

“Most people tell us the same thing. Let me ask you a question. In the summer, is the air warmer inside your crawl space or outside?”

“Outside of course.”

“What happens when warm air hits cold air?”

“Well, it condenses.”

“Exactly. So, warm air outside your home comes into contact with cooler air inside your crawl space, thanks to those foundation vents and the air condenses.”

“I hadn’t really thought about it that way, but you’re probably right.”

The reality is that warm, moist air outside your home circulates into your crawl space through those foundation vents. As that warmer air cools, it condenses. Sixty-five percent relative humidity in the outside air can actually become air with 85 or 95 percent relative humidity once it cools in your crawl space.”

“That’s really humid.”

“Yes, it is. It’s almost like being in a tropical rain forest. We’ve seen many homes in West Virginia that have water dripping off the floor joists and soaked insulation because of those foundation vents. Under those conditions, mold can start growing within a few days.”

“So, what should I do with those vents?”

“If you use those vents to dry out your crawl space you should close those vents in the summer and open them in the winter when the air is a lot drier.”

“That would be crazy. Wouldn’t that make my crawl space and floors very cold in the winter and perhaps even freeze my water pipes?”

“Yes, it would and yes, your pipes could possibly freeze.”

“OK, so what’s the solution?”

“Basement Authority of West Virginia and most experts now recommend first getting rid of any water in your crawl space, then encapsulating your crawl space, sealing out all outside air, and then sealing out moisture from the ground and even moisture from your foundation walls. This makes the air inside your home much healthier, your crawl space much warmer and also prevents moisture from rotting the wood under your home.”

“I was actually thinking about putting in those automatic vents. You know, the ones that open when it’s warm and close when it’s cold. It sounds like those are a bad idea.”

“You would be wasting your money with those. They do more harm than good in most cases. The EPA is now saying that in most cases, foundation vents do more to wet your crawl space than dry it out. The EPA is now saying that these vents can actually encourage mold growth. Building codes are starting to change all over the country to encourage this encapsulation approach. Sadly, some contractors still build homes the ‘old’ way with those foundation vents. But things are starting to change for the better as builders and homeowners become educated on this subject and as building codes change.”

“I’m sure glad I talked with you. I’m not sure I want to do this work myself. Do you provide free inspections?”

“Yes, we do.”

To schedule a free, no obligation inspection of your crawl space, call Basement Authority of West Virginia.

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Charleston, WV

132 Rocky Step Rd.,
Scott Depot, WV 25560