Crawlspace vents - Carolina Country

Crawlspace vents

By Hannah McKenzie

Crawlspace vents
Vents can ventilate a crawlspace to prevent the build-up of dangerous gases, such as radon, and cut down on the moisture found under the home.

Q: I would like to replace the raggedy crawlspace vents under my home. What kind of replacement vents are the best?

A: It is a relief to have choices at the hardware store, but it gets confusing when there are too many options. Crawlspace vents are those 8-inch tall, 16-inch wide holes scattered around the perimeter of most foundation walls in North Carolina. They are intended to ventilate the crawlspace to prevent the build-up of dangerous gases, such as radon, and cut down on the moisture found under the home.

There are two kinds of crawlspace vents:

Automatic crawlspace vents close when it is 40 degrees or colder to lower the chances of freezing pipes and open when it is warmer. Automatic vents are notorious for not working and having a short lifespan. Inspecting them once a year is highly recommended.

Manual crawlspace vents allow a diligent homeowner to open and close them as the temperatures rise and fall and the seasons change. Vents should be open most of the year to minimize radon gas and moisture build-up under a home.

Pest entry is another important consideration when selecting crawlspace vents. Crawlspaces are safe havens for pesky critters. For years, I naively only worried about opossums, raccoons, cats, snakes and mice seeking shelter under my home. After this wonderfully wet summer, everyone is noticing more cockroaches in their homes; which can fit through a 1/16 inch crack. Select a crawlspace vent with a durable mesh screen and seal it to the foundation wall so pests cannot enter around the frame.
While you are poking around the outside of your house, take this opportunity to fix other problem areas.

Trees and vegetation should be trimmed 18 inches away from your home’s exterior. Plug and seal any holes and cracks in the foundation walls to prevent pests and water from entering. Make sure gutters are clear of debris and downspouts direct water away from your home. Moist foundations may contribute to structural problems, jump-start fungal growth and lure a variety of pests.

Peak inside the crawlspace to ensure there are no puddles of water under your home to attract cockroaches and other pests. Once they are under your home, it is very convenient for them to mosey into the kitchen for a swell dinner of crumbs or head to the bathroom for some delicious toothpaste residue.

Closed crawlspaces

An alternative to maintaining a vented crawlspace is to create a closed crawlspace. This entails more than just closing the vents and installing a dehumidifier. It involves a variety of parts that work together as a system and requires making safe choices with gas appliances that may reside there. Full details can be found at or by calling (919) 857-9000.

Vented crawlspaces are common in North Carolina homes. They have worked well in the past and they may continue to work well in the future. But, because every home and its location is different, if you find your vented crawlspace is wet, musty and will not dry out, a properly closed crawlspace may be a much better option than your current vented crawlspace. The North Carolina research results on will tell you more.

About the Author

Hannah McKenzie is a residential building science consultant at Advanced Energy in Raleigh who specializes in working with nonprofit developers like Habitat for Humanity to make new affordable housing energy efficient.

Comments (2)

  • Are foundation vent wells legal in North Carolina?

    MW |
    September 29, 2019 |

    • Hi, MW – we sent your question to Jonathan Coulter, building science specialist at Advanced Energy, and he had this response:

      “Yes, not only are they legal, they are recommended in some situations. According to Section R408.1.2 ‘Foundation vent location’ of the 2018 North Carolina Residential Code (, it states that ‘vent dams shall be provided when the bottom of the foundation vent opening is less than 4 inches above the finished exterior grade.’”

      Carolina Country |
      October 11, 2019 |

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