Crawl Space Vapor Barriers: What Atlanta Homeowners Need to Know

A vapor barrier is the foundation of any crawl space moisture control system. But not all vapor barriers are equal, and a poor installation can actually make things worse. Here's what you need to know about vapor barriers—including common mistakes that waste money.

What a Vapor Barrier Actually Does

A crawl space vapor barrier is a sheet of plastic laid over the dirt floor of your crawl space. Its job is straightforward: block moisture from the ground from evaporating into the crawl space air. Without a barrier, your crawl space's exposed soil constantly releases moisture vapor. In Atlanta's humid climate, this ground moisture combines with already-humid outdoor air entering through vents, creating the perfect environment for mold, wood rot, and pest infestations. A properly installed vapor barrier eliminates the largest single source of crawl space moisture.

Thickness Matters: Understanding Mil Ratings

Vapor barriers are measured in "mils" (thousandths of an inch). A 6-mil barrier is the bare minimum code requirement—it's thin, tears easily, and degrades within a few years. We don't recommend it. A 12-mil barrier is a decent mid-range option. For full crawl space encapsulation, 20-mil is the industry standard—it's puncture-resistant, won't degrade for decades, and provides a true sealed environment when combined with wall coverage and sealed seams.

Ground-Only vs. Full Encapsulation

There's a big difference between laying plastic on the dirt and full encapsulation. A ground-only vapor barrier covers just the floor—it helps with ground moisture but doesn't address moisture entering through walls, vents, or the air. Full encapsulation covers the floor AND walls, seals all vents and seams, and typically includes a dehumidifier. For Atlanta's humidity levels, full encapsulation provides dramatically better results.

Common Installation Mistakes

The quality of installation matters as much as the material. Common mistakes include not overlapping seams enough (should be at least 12 inches and sealed with tape), not extending the barrier up foundation walls, leaving gaps around piers and support columns, not securing the barrier properly, and failing to address existing water intrusion before installing. The worst mistake: laying a vapor barrier over standing water or saturated soil. The barrier traps the water underneath and creates a breeding ground for mold. Water issues must be resolved first.

Do You Need a Dehumidifier Too?

In Atlanta, almost always yes. Even with a perfect vapor barrier, moisture enters crawl spaces through foundation walls, air leaks, and seasonal humidity changes. A commercial-grade crawl space dehumidifier maintains humidity below 60% year-round—the threshold below which mold cannot grow. Residential dehumidifiers from hardware stores are not sufficient for crawl spaces—they lack the capacity and aren't designed for the conditions.

Cost Expectations

A basic ground-only vapor barrier installation costs $1,500 to $3,000 for most Atlanta homes. Full crawl space encapsulation with 20-mil barrier, wall coverage, vent sealing, and dehumidifier typically costs $5,000 to $12,000 depending on crawl space size and condition. While the upfront cost is higher, encapsulation pays for itself through reduced energy bills, eliminated mold remediation costs, extended HVAC lifespan, and preserved structural integrity. At Reliable Solutions Atlanta, we assess your crawl space and recommend the level of protection your home actually needs. Call 770-895-2039 for a free inspection.