Choosing the right crawl space vapour barrier thickness makes a big difference to how long it lasts. A 6 mil sheet is often treated as the basic minimum, but it tears easily during installation and later maintenance. A 10 to 12 mil barrier is a good balance of strength and cost for most Lower Mainland homes, while a reinforced 15 to 20 mil liner suits crawl spaces used for storage or with a furnace or water tank that needs service. Learn what thickness of crawl space vapour barrier to use.