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There’s a process that must be followed when it comes to installing a crawl space vapor barrier. In this guide, we’ll cover how you can install a crawl space vapor barrier in your home. We will assume that your crawl space has already been inspected and you are able to encapsulate the crawl space.

How To Install A Crawl Space Vapor Barrier

  • Moisture is a common problem with many crawl spaces around the country. What you don’t want is water coming into the crawl space. You need to add perimeter drains to ensure that there will be no water drainage in your crawl space. Make sure you do slope your outside drains appropriately so water can run and drain as needed.
  • Once that is done, you need to clean your crawl space floors. Make sure you get all objects out of the way. If you have a crawl space that has sharp objects in the dirt and they won’t come out, you’ll likely need a 2o mil crawl space vapor barrier. If you will have heavy foot traffic or storage on the crawl space floor, we’d also recommend using a 20 mil vapor barrier size. If the crawl space is smooth, we’d recommend using a 12 mil size. Due to our experience working with crawl space vapor barriers, if you do use a 12 mil or 20 mil, we would recommend the SilverBack crawl space vapor barrier brand.
  • When laying your vapor barrier on the floor, you want to make sure you overlap all seams. The recommended length is at least 12 inches. Each seam should then be taped using crawl space seal tape. Do make sure you’re using the right tape and make sure you don’t do a sloppy job here. Make sure the liner is clean and tape each seam. The correct tape to use is waterproof seam tape.

  • We do recommend using insulation on your crawl space foundation walls. We recommend using rigid foam as it soaks up less moisture than other insulation types. Once the insulation has been added, you can add your 12 mil liner on the outside. If you don’t add insulation on the foundation walls, it’s going to be tough to maintain the home environment.
  • You also want to use new insulation for your rim joist. If the crawl space wasn’t sealed prior, chances are this insulation (if you had insulation there prior) contains moisture. Take this down, make sure the space is dry and insert the new insulation.
  • If you need a more detailed approach and step-by-step direction that includes measuring the crawl space, we suggest this article by Matt Leech of  How To Install A Crawl Space Vapor Barrier
  • Once the crawl space is sealed, you will then need to condition the air. There’s a few ways that you can do this. The most common way and the most efficient is adding a crawl space dehumidifier. The dehumidifier will turn moisture vapor to liquid vapor. Due to this, you’ll need sump pump to remove the water.


You don’t hear about 6 and 8 mil crawl space vapor barriers as much as you do the 12 and 20, but it doesn’t mean they’re less important. We commonly hear about the 12 mil vapor barrier and 20 mil vapor barrier when we’re discussing crawl space encapsulation. What you don’t hear about is the 6 mil liner and 8 mil liner. But why?

For one, most crawl spaces are large and require a thicker vapor barrier. For two, crawl space floors are often tough. Due to this, it’s recommended to at least use a 12 mil vapor barrier for your flooring.

You can also find this brand in a 6 mil, the 6 mil DiamondBack vapor barrier.

We’ve learned that the 8 mil liner is great for encapsulating walls and piers. Again, rarely do we use 8 mil liners on the floor. Even with no storage on the vapor barrier, it would be best to use a 12 mil vapor barrier at the least and a 20 mil vapor barrier if you’ll have heavy traffic and storage.