Crawl Space Foundation Vents: Can You Really Seal Them Up?

Homes built on a crawl space need ventilation. However, that does not mean that they require foundation vents to the outside, as many homes currently have. According to the International Residential Code (IRC) 2006 and 2009, Section 408.3 states:

Ventilation openings in underfloor spaces specified in Sections R408.1 and R408.2 shall not be required where:

1. 1. Continuously operated mechanical exhaust ventilation at a rate equal to 1.0 cfm (0.47 L/s) for each 50 ft² (4.7 m²) of crawlspace floor area, including an air pathway to the common area and perimeter walls insulated in accordance with Section N1102.2.8.
   2.  Conditioned air supply sized to deliver at a rate equal to 1.0 cfm (0.47 L/s) for each 50 ft² (4.7 m²) of under-floor area, including a return air pathway to the common area, and perimeter walls insulated in accordance with Section N1102.2.8.

So, the answer to the question “Can I really seal them up? ” is YES. Crawl space vents can and should be sealed up once you have selected a continuous crawl space moisture vapor barrier and are ready to install it. In fact, in order to properly encapsulate a crawl space, any vents must be fully sealed and closed.

The advantages of sealing foundation vents actually go beyond the moisture control aspects. Every winter, that cold kitchen or bathroom floor reminds us that we need to get some insulation in the crawl space. However, in order to effectively warm an area, you first have to prevent cold air from entering the area. Closing and sealing off the foundation vents will reduce your heating costs, warm your floors, and prevent water pipes from freezing.

This all being said, do remember: DO NOT CLOSE YOUR VENTS UNLESS YOU ARE GOING TO ENCAPSULATE AND FULLY SEAL OFF THE CRAWL SPACE FROM THE SOIL. If you attempt to fix one issue in your crawl space without first dealing with other “known” problems, you definitely risk worsening your crawl space headache. Do your research and educate yourself before taking action!