Crawl Space Foundation Vents: Open or Cl​osed?

Today we are going to write about the debate of open versus closed crawl space vents. Homes have been built with crawl spaces for years, and this also includes crawl space vents. Nearly all homes that were built on a crawl space have a crawl space vent. So if nearly all homes have them, then they must be a good thing right? Well to answer that question we must dive a little deeper.

Crawl space vents were originally installed to prevent the build up of moisture within in the crawl space. If you have a constant flow of air coming throughout a structure, then moisture would not have a change to build up beneath the home. This may have worked in the past, but as time and building practices have adapted so have the way crawl spaces are treated. Crawl spaces are being given more attention than ever, and recent studies have found it is actually best to close off your crawl space vents.

Setting aside the recent studies performed, and using just natural logic, it makes all the sense in the world to close off your crawl space vents during all seasons. Lets say that you live in Indiana and it is the middle of summer. Indiana can easily approach 90 degree temperatures with nearly 85 percent humidity in the summer. Now if you leave your crawl space vents open, then you are going to allow that hot humid air to slowly enter into your crawl space.

So now you have a crawl space that is approaching the same conditions as the outside environment. Well its not like you live under your crawl space, so that really isn’t a problem is it? Unfortunately yes it is. All that separates you from your crawl space is typically a 3/4 inch piece of subfloor, maybe a vapor barrier, and whatever flooring style you have installed in your home. Thus making it very easy for crawl space air to transition into your home.

If you remember in science class, you were taught that hot air rises? Well if you have left your crawl space vents open, and allowed that 90 degree air into your crawl space then it will naturally rise. IN FACT, nearly 50 percent of the air we breath in 1 story homes comes from the crawl space. Thus making your home more humid, leading you to feel more uncomfortable, and making your AC unit work harder. If your AC unit has to work more often to keep up with the additional temperature swings due to the hot air from the crawl space rising up, then that is going to cost you more money due to higher utility bills.

From a moisture control standpoint, allowing humid air into your crawl space is a very bad idea as well. Mold needs moisture to grow and take hold in your crawl space. Without it, there is no way for it to spread and colonize in your crawl space. IN FACT, Mold is unable to grow below 60 percent humidity.

So doesn’t it make more sense to close the vents off and properly keep humidity in the crawl space below 60 percent? Yeah, we thought so too. That is why we joined the crawl space encapsulation business, because that is precisely what crawl space encapsulation does.

In closing, the next time you hear someone tell you to open your crawl space vents in the summer to “dry it out”; maybe send them this page link to help them out. If you are worried about your crawl space or simply have a question that needs answered, then please reach out and we will help you in any way possible.