Whether entering from vents, plumbing leaks, or through porous block walls, water in the crawl space is never a good sign. Moisture and standing water attract bugs and other pests, leads to wood rot and weakening support systems, and contributes to mold and mildew growth on insulation and throughout the crawl space and home.
Humidity is another culprit that can wreak havoc on your living environment. The ideal range for humidity in your home is 35 to 40 percent. If it is above 50 percent, you need to take action such as running a dehumidifier. (Source: Bob Vila).
It is common for crawl spaces to have high relative humidity and moisture, which promotes mold growth, especially on organic materials like wood and insulation. The moisture that accumulates in a crawl space may also enter another part of the building and contribute to mold growth there. Moisture can pass from a crawl space into a building through cracks in walls, floors and ceilings. (Source: EPA)