Should I Close My Crawl Space Vents?



Should my crawl space vents, aka foundation vents or house vents, be open or closed? It's a current hot topic for homeowners. For decades, building codes have stated that keeping your crawl space vented is essential to controlling the moisture under your home and only recently have we started to question this logic. 


Let's first talk about that logic and why there is a debate to have open vents in the crawl space. 


1. Houses used to be simpler, just a rectangular house with foundation vents on either side which made it easier for air to travel in and out of the crawl space.


2. In dryer climates, they work much more effectively by giving your crawl space good air circulation in the warmer months, without the worry of bringing in moisture.


3. They give harmful soil gases and other gases like radon an outlet to escape instead of drifting into your home for you to breathe in.


So it may be easy to see why it has been overlooked for so long and still is a debated topic. But in high humidity states like Western Kentucky -where I operate- there is no debate. It is simple, you need to close your crawl space vents. First though, you need to take all factors into consideration. Let's talk about why open vents can be harmful to the well being of your home.


1. Houses are getting bigger all the time. Before, the air had an easier route in one vent and out the other side, now it has more area and often center foundation walls to go around before going back out. So instead of creating "air flow", now you are just letting in hot, humid, moist air to enter and linger in your crawl space. When you allow moisture to enter at a consistent basis, you are creating the perfect habitat for mold and fungus to grow.


2. If your HVAC system is in the crawl space and you are running the AC in the summer. That hot, humid air coming in those open crawl space vents will hit the HVAC duct work and cause condensation. Producing moisture and exposing all the wood around that duct work.


3. You allow an entrance for termites, snakes, and other pests to inhabit your crawl space. (Which they will, if it is nice and damp in there)


4. If you don't make sure that the vents are high enough off the outside soil, when it rains you can have water entering your crawl space through your vents at a rapid rate.


Now you may want to close your computer or put down your smart phone and go close your vents right now, but there is still one significant issue to consider when you close your crawl space off from the outside. That issue is soil gases and radon. You should take the appropriate steps in ensuring that you are not putting yourself at risk to breathe in these gases when you're in your safe place -your home. 


Here are some things to consider when closing your vents; Do you have a vapor barrier or encapsulation to block the gases from easily leaving the soil? Do you have an exhaust fan or other form of process to keep the crawl space in a negative pressure and remove those harmful gases before they raise up into the living space of your house? Lastly, do you have a way to check the humidity levels in your crawl space to be sure it has the right climate to keep mold and rot from forming?

There is always a cause and effect for what we do. If it was as easy as, ''hey we were wrong, vents should be closed", it would have already become the official code. So just make sure that if you decide to close your vents, find someone knowledgable who will consider your individual home and circumstances to keep you and your family safe.






-Written by Lee Sell

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