Crawlspace Vent Dilemma

Homeowners ask a variety of important questions. One of the most frequently asked questions we receive is, “Should my crawlspace vents remain open or closed?” There are some valid points on both sides and we will try to navigate this often-asked question.

Opinion #1: Crawl space vents should remain closed at all times. The crawl space should be encapsulated so that there is no outside air coming into the space and the humidity level is controlled internally. This is done by laying a “Vapor Barrier” over the earth and running the barrier up the walls and sealing it so that no water vapor makes it’s way into the space. Secondly, all of the vents are sealed with foam insulation and, lastly, a dehumidifier is sized and is installed and set to 40%-45% humidity. If there is mold on the floor joists or sub floor, this should be dealt with prior to encapsulation.

Opinion #2: Crawlspace vents should be open in summer months and closed during the winter months. The thought here is that the humidity level in the winter is a bit lower allowing the vents to be closed and keeping the warmer, drier air inside of the crawl space. During the summer, the theory is that the crawl space vents should be open to allow air-flow and keep the humidity lower by bringing in outside air into the crawl space. It is also important that there is a vapor barrier on the earth in the crawl space and that it is laid correctly. When temperatures get to 40 degrees or below, it makes sense to close the vents so that the pipes don’t freeze and the home stays a bit warmer.

Opinion #1 is far and away the most expensive, but it also makes the most sense and eliminates the risk of mold growth due to humidity.

It should be noted that most remediation companies will give an in-depth cost estimate to encapsulate a crawl space. Lastly, if the cost is too high to perform encapsulation, keep a close eye on your crawlspace and the humidity levels. Make periodic checks to make sure mold is not forming on floor joists, that the vapor barrier is in good shape and that there have been no recent water intrusions.