the solution requires isolating the crawl space from the those conditions. A complete vapor barrier covers the ground, foundation walls, and piers. The crawl space vents are sealed. And, ideally, insulation on the foundation walls minimizes heat loss and heat gain.
Although crawl space encapsulation is perhaps the most common term for this treatment, some other names apply as well: Sealed crawl space, closed crawl space, and conditioned crawl space are the most common alternatives. Encapsulated, sealed, and closed all refer to isolating the crawl from ambient conditions. Conditioned states that the crawl space is inside the building envelope and is either directly or indirectly conditioned through its connection to the house.
Encapsulating your crawl space has many advantages. See the previous page of crawl space problems, and eliminating or reducing those gives you some immediately obvious advantages. Basically, though, the advantages are that the house is more comfortable, durable, healthful, and efficient.
Keeping the crawl space at temperatures and humidity levels closer to those in the house than the outdoors means greatly improved comfort. No more cold floors or muggy air in the house. In a house with a typical vented crawl space, when the outside temperature is 30 degrees, the crawl space temperature is going to be not much higher than that. If the floors in that house are uninsulated or poorly insulated, that means a lot of heat loss through the floors.
In contrast, we see crawl space temperatures within 5 or 10 degrees of the house temperature after they're encapsulated. In a recently completed project, the outdoor temperature was 29 degrees when we checked up on the house. The indoor temperature was about 74 (the homeowner likes it really warm), and the crawl space temperature was 70 degrees.
As for durability, when the humidity of the air around the floors is kept low, the moisture content of the wood goes down, making it less appetizing to termites, mold, and wood decaying fungus. (Treating microbial infestations such as mold without reducing the source of moisture makes little sense and is just an invitation for further problems.) Also, we treat the wood that is near the foundation walls with borate to reduce problems from wood destroying insects, wood decaying fungus, and mold.
Indoor air quality improves because less moisture in the crawl space means you're not growing as many things down there. Also, you're not bringing in all that outside air, with its dust and pollen. The infiltration rate in the home is reduced because of the air sealing. And you don't have all those critters creating waste down there.
The efficiency improves because of the temperature differences explained above, but also many crawl spaces have duct work. Bring those ducts inside the building envelope, and the heating and air conditioning system won't have to work so hard.
Finally, although this list isn't exhaustive, one more benefit is that an encapsulated crawl space is suitable for storage (see photo at right). You don't want to put lawn mowers and pesticides there, but other objects will remain in good shape when stored in a this type of crawl space.
The Method. The next page in this series of articles describes how Energy Vanguard encapsulates crawl spaces using methods and materials that ensure the job is done right and will last a long time.
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CAUTION: Encapsulating a crawl space can create new problems if it's not done correctly. In some cases, a crawl space should not be encapsulated. Two big issues that must be looked at carefully are bulk water problems and the possibility of backdrafting combustion appliances in the crawl space. Pest control also places some restrictions on the details of encapsulation. For the best info available on this topic, go to Advanced Energy's website and download their guidelines, titled "Closed Crawl Spaces: An Introduction for the Southeast." Crawl space encapsulation is not suitable as a DIY project in most cases, so learn what you can and then call in a professional.