Pondering Crawlspace Vents

By Hannah McKenzie | September 29, 2014

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

A: Crawl space vents are those 8-inch-tall, 16-inch-wide holes scattered around the perimeter of most foundation walls. They are intended to ventilate the crawl space to prevent the buildup of dangerous gases, such as radon, and to cut down on the moisture found under the home. There are two kinds of crawl space vents.

Automatic crawl space vents close when it is 40 degrees or colder to lower the chances of freezing pipes; they open when it is warmer. Automatic vents are notorious for not working and having a short lifespan. Therefore, inspecting them once a year is highly recommended.

Manual crawl space vents allow a 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 buildup under a home.

Pest entry is another important consideration when selecting crawl space vents. Crawl spaces are safe havens for pesky critters. Select a crawl space 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 crawl space to ensure there are no puddles of water under your home, as these will attract cockroaches and other pests. Once critters enter the crawl space, it is very convenient for them to mosey into the kitchen or bathroom.

An alternative to maintaining a vented crawl space is to create a closed crawl space. 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 in the crawl space.

Closed crawl spaces offer numerous benefits:

  • Additional moisture control, which means reduced opportunity for mold growth
  • Lower relative humidity within the home during summer months
  • Less dry-feeling air during winter months
  • Fewer opportunities for pest entry
  • Potential improvement of indoor air quality
  • And if your HVAC system is in the crawl space, possible savings of up to 15 percent on heating and cooling bills

Vented crawl spaces are common in homes. They have worked well in the past, and they may continue to work well in the future. However, because every home is different, if you find your vented crawl space is wet, musty and not drying out, a properly closed crawl space may be a better option.