A crawl space drain is a system that drains excess water out of a crawl space, thereby preventing mold and wood rot. Crawl space drains may use different technology depending on the size and material of the crawl space floor and walls.
In crawl spaces with packed dirt floors, a drainage system often consists of a perforated or "d" shaped pipe line running along the walls just below the elevation of the floor. Excess moisture from the walls and floor collects in the pipe. Usually, the pipeline drains into a small tank or pit located at the lowest point in the crawl space, and the collected water is intermittently pumped outside the house.