I’ve heard about crawl space encapsulation, am I better off sealing the vents?

I’ve heard about crawl space encapsulation. Am I better off sealing the vents to my crawl with a rigid foam board or insulating between my floor joists and keeping the space ventilated?

If you have or want a non ventilated sealed crawl space, full encapsulation, then you probably don’t need to add floor insulation. Traditionally, crawl spaces have been vented to prevent problems with moisture. However there are a growing number of building professionals that recognize the benefits of a moisture controlled unventilated crawl space.

There are two main reasons for this line of thinking:

• Ventilation in the winter makes it difficult to keep crawl spaces warm.


• Warm, moist air brought into the crawl space through foundation vents in the summer is often unable to dehumidify a crawl space. In fact, this moist outdoor air can lead to increased moisture levels in the crawl space. This information is from US Dept of Energy website.

For a more complete discussion on encapsulated crawl spaces please see our section on crawl spaces in this website.