All crawl spaces are a little different. Most crawl spaces are either dirt or covered with gravel. The old code was to have airflow from the outside into the crawl space. That has been changed because outside humidity has entering the area and causing mold issues. Now it is recommended to cover the area with a heavy vapor barrier and seal it to the walls.
Crawl spaces with dirt and gravel floors are good radon entry points. Once the vapor barrier is applied and suction under the vapor barrier from a radon fan is introduced, the radon along with musty smell and other contaminates are removed and vented above the roof. Homeowners usually notice a fresh smell and no more musty odors.
We recommend a 12 mil white jacket as a vapor barrier, it holds up well and looks nice. Different than plane 6 mil plastic that cracks over time plus not have enough to crawl on without tearing.
Our photo gallery shows numerous crawl space covers.
