How Much Vapor Barrier Do I Need for My Crawl Space?

There are so many benefits to encapsulating your crawl space—eliminating moisture damage, preventing deterioration and increasing energy efficiency, to name a few. Whether you are embarking on a DIY crawl space encapsulation project or installing a vapor barrier for a client, the first step is to determine how much vapor barrier material you’ll need to purchase.

Crawl spaces vary in size, but the minimum recommended height between the ground and the floor joists is 18 inches, with a maximum of approximately four feet. And while that may not sound nearly large enough for a full-grown human to enter—let alone, move around in—they don’t call it a “crawl space” for nothing.

In truth, there isn’t a one-size-fits-all vapor barrier, but we are here to help you determine just how much material you’ll need to get the job done.

Measure Twice, Cut Once

Before making a purchase, you must first determine what size vapor barrier you’ll need to encapsulate your space—and unless you’ve got the blueprint to your house handy, you’ll need to do some measuring. Fortunately, measuring for a crawl space vapor barrier is fairly straightforward. Grab a tape measurer, head into your crawl space (watch your head!) and measure the length, width and height of the walls. For odd-shaped foundations, you’ll want to measure by sections or rooms. Be sure to measure around any columns or piers, as they will need to be covered as well for optimum energy efficiency.

Calculating How Much Vapor Barrier You Need

Once you have the measurements of your crawl space, it’s time to calculate how much material you’ll need to cover the walls and floor. (Note: walls and floors should be calculated separately.)

The amount of material you need for the wall—also known as the perimeter—is calculated using the width, length and height of the crawlspace:

1. Add the length and width of the space.
2. Multiply that number by two.
3. Then multiply the results by the height. This will give you the square footage needed for the wall.

Since most walls are less than four feet, we typically recommend a four- or six-foot wide roll, which should give you more than enough length to overlap the wall vapor barrier with the floor panels.

Measuring the floor is also quite simple—

Just multiply the width by the length to get the total square footage needed for the ground. The wider the width of the material, the fewer seams you will require when overlapping panels, so often a 12’ wide roll works best for floors.

*Important note: You should account for an additional six inches or 10% of overlap between panels.

For more help, check out this video demonstration of how to measure your crawl space.

Seal the Job with Vapor Barrier Tape

Tape is an essential part of the vapor barrier installation process, as you’ll need it to overlap panels and seal the material to the wall. We generally recommend two types of tape for your crawl space application:

Vapor Tape can be used to create a waterproof seal and a clean finish. The general rule of thumb with vapor tape is one roll for every 1,000 square feet of vapor barrier.

Butyl Tape is an aggressive, self-healing, double-sided tape used to adhere the crawl space liner to the wall and seam the overlapping vapor barrier panels (where applicable). The amount of butyl tape you’ll need is based on the perimeter of the entire space, including any columns.

In addition to tape, you’ll need a fastener to keep the vapor barrier attached to the foundation wall. We recommend our Christmas Tree Ratchet Fasteners — they can be easily installed with a drill bit every 18-24 inches through the butyl tape, creating an airtight seal around the hole.

We’ve Got Crawl Spaces Covered

Americover is a leading source for high-quality, American-manufactured crawlspace vapor barriers and liners.  When installed properly, a top-quality vapor barrier can last you 20 years or more. Discover which size vapor barrier is right for your crawl space, and when you are ready to purchase, visit our online store to order yours and have it delivered right to your house or jobsite.