There are several options on how to handle the foundation type of a home with a crawl space, whether you own one currently, or are thinking of buying/building one. Generally, crawl spaces are vented to the outside, but more recently, over the last decade at least, more energy efficient homes have been encapsulating the crawl spaces. This technique has become popular because it is generally considered to be the best way to prevent the moisture problems of vented crawl spaces. This is particularly impactful in humid climates. In dry climates, encapsulating the crawl space may not be worth the money.
Read the full article here: Five Ways to Deal with Crawl Space Air