A vapor barrier, sometimes called a moisture barrier, is the foundation of a dry crawl space. It stops moisture in the soil from evaporating into the space under your house. Here's how barriers compare, what thickness to look for, and when you need more than a barrier alone.
Vapor barrier vs. full encapsulation
| Vapor barrier only | Full encapsulation | |
|---|---|---|
| Floor covered | Yes | Yes |
| Walls covered | Usually not | Yes |
| Seams and edges sealed | Sometimes | Yes |
| Vents and gaps sealed | No | Yes |
| Humidity control | No | Usually a dehumidifier |
| Typical liner | About 6 mil | About 10 – 20 mil, often reinforced |
| Best for | Mild dampness | Musty odors, mold, high humidity |
What thickness to look for
- 6 mil: a basic ground cover. Inexpensive but easy to tear.
- 10 to 12 mil: a common middle ground for many encapsulation jobs.
- 15 to 20 mil, reinforced: the heavy-duty choice. It holds up to foot traffic, storage and service visits.
Heavy 20 mil liner material typically costs about $0.40 to $0.70 per square foot before labor, according to This Old House and HomeAdvisor. See the full encapsulation cost guide.
Need a new vapor barrier or a full encapsulation? Call for a quote.
Call: (317) 426-0557Signs your vapor barrier isn't working
- Tears, gaps or sections that have pulled away or shifted.
- Water pooling on top of the plastic.
- Musty odors in the house despite having a barrier.
- Condensation on pipes, ducts or the underside of the floor.
- Exposed soil around the edges and piers.
What a good installation looks like
- Liner overlaps at the seams, and seams are taped.
- Liner runs up the foundation walls and is fastened and sealed at the top.
- Piers and posts are wrapped and sealed.
- Any water problems are fixed before the liner goes in.
Frequently asked questions
What thickness vapor barrier should I use in a crawl space?
Basic ground covers are often 6 mil polyethylene. For encapsulation, contractors commonly use 10 to 20 mil liners, often reinforced, because they resist tearing and hold up better if anyone crawls or stores items on them.
Is a vapor barrier the same as encapsulation?
No. A vapor barrier usually just covers the floor. Encapsulation covers the floor and walls, seals seams, vents and gaps, and adds humidity control.
How long does a crawl space vapor barrier last?
A heavy, well-installed liner can last many years, often backed by long manufacturer warranties. Thin plastic can tear, shift or degrade much sooner, especially if the space is used for storage.