Crawl space

[1] The crawl space's functions include providing access to repair plumbing, electrical wiring, and heating and cooling systems without the need for excavation.

[2] The crawl space can provide a protective buffer between the damp ground and the wooden parts of a home and, with adequate sealing, help with radon mitigation.

The Federal Emergency Management Agency recommends that the floor of the crawlspace be at or above the lowest grade adjacent to the building.

[3] Crawl spaces are not usually an option in cold regions, such as the northern United States, where a full basement is needed to get the foundation below the frost line.

[5] However, in regions with a humid climate, vents to the outside can also allow moist air to come in, which can then condense if temperatures (e.g. on cooler surfaces such as ductwork) drop below the dew point, creating a damp environment that is hospitable to indoor mold growth as well as infestations by rodents and insects, possibly including wood-damaging ones such as termites[1] or carpenter ants.

Even without condensation, relative humidity above 80% can support mold growth and rot wooden structural materials such as floor joists.