What Exactly Is a Dry Space Vapor Barrier?

Imagine a robust, heavy-duty liner specifically designed to separate your home from the damp earth below. That’s essentially what a crawl space vapor barrier is. More than just a simple tarp, it’s typically a thick, durable sheet of polyethylene plastic (often 10-20 mil thick, much thicker than standard construction plastic) that is meticulously installed across the entire floor of your crawl space.

Its primary purpose is elegantly simple yet incredibly powerful: to block moisture evaporation from the soil. The ground beneath your home naturally releases moisture into the air. Without a barrier, this moisture rises, creating the humid, damp environment we discussed earlier. A vapor barrier acts as an impermeable shield, preventing this ground moisture from ever becoming airborne within your crawl space.

When properly installed, the vapor barrier covers 100% of the crawl space floor, and often extends several inches up the foundation walls. All seams are meticulously overlapped and sealed with specialized tape, creating a continuous, protective membrane. This transforms your crawl space from an open, earth-exposed area into a much drier, more controlled environment, directly addressing the root cause of many common crawl space issues. It’s the foundational step towards a truly healthy and dry crawl space.