In North Carolina, where I live and work, enclosed crawlspace foundations with small vent openings are very common. Most of those crawlspaces experience high humidity, and many have problems with mold and rot.
My contracting firm, The Healthy Building Company, specializes in sealed and insulated crawlspaces, which the newest version of the International Residential Code now allows. Instead of vents, a sealed crawlspace has a continuous vapor barrier to keep ground moisture out of the space.
to read the full article.