A crawl space vapour barrier tossed loosely on the dirt won’t do much. A proper install starts by fixing drainage and gutter problems, then clearing sharp rocks, old wood and fallen insulation. The barrier is laid with generous taped overlaps, run up the foundation walls and sealed, and cut tightly around piers and pipes so it stays continuous. Insulating the walls and rim joists finishes the job. See the full crawl space vapour barrier installation steps.