Overview
A crawl space is an unoccupied, unfinished, narrow space within a building, between the ground and the first (or ground) floor. The crawl space is so named because there is typically only enough room to crawl rather than stand; anything larger than about and beneath the ground floor would tend to be considered a basement.
Uses
A crawl space is often built when building a basement would be impractical. A crawl space can also substitute for a concrete slab foundation that would hinder building inspections.
The crawl space's functions include providing access to repair plumbing, electrical wiring, and heating and cooling systems without the need for excavation. Building insulation can also be installed in a crawl space. 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. Crawl spaces are also sometimes used for storage of items such as canned goods that are not particularly susceptible to destruction by mildew or unstable temperatures.
A crawl space foundation can be used to elevate the lowest floors of residential buildings located in Special Flood Hazard Areas above the Base Flood Elevation. The Federal Emergency Management Agency recommends that the floor of the crawlspace be at or above the lowest grade adjacent to the building.
From Wikipedia (CC BY-SA 4.0).