Over 25 million homes in the U.S. are built over exposed dirt crawlspaces. The U.S. Department of Energy and independent building science research groups have found exposed dirt crawlspaces cause moisture problems, pests, and high energy bills. Basically, what is under the house should be treated as part of the house. The environment under the house effects the indoor environment. Leaving the crawlspace exposed causes problems such as high humidity, rotting wood floor joists, mold, mildew and pests. If we know leaving a dirt crawlspace as is isn't an option, you need to do something about it.
There are two approaches to fixing the problem: installing a plastic liner and encapsulating the crawlspace or pumping a concrete floor into the crawlspace. While concrete may fix the aesthetic problems of exposed dirt crawlspaces, it does not fix the moisture problems. Concrete is porous meaning moisture can travel through it. Researchers found installing a plastic liner system in the crawlspace and closing the vents is a better option to solving humidity problems. Advanced Energy's ground-breaking research in 2005 changed the building codes regarding vented crawlspaces in North Carolina. The study proved that closed crawlspaces using a plastic liner system solves the humidity problem in crawlspaces and leads to better energy efficiency. The Department of Energy has since adopted the new found knowledge saying a properly sealed and insulated crawlspace will save energy costs and improve comfort levels and durability of a home. It will reduce moisture, radon, and other pollutants and pests that often enter the home through an exposed dirt crawlspace.