Moisture is one of those unseen threats that can quietly wreak havoc on a building. Left unchecked, it leads to rotting wood, mold growth, electrical failures, and even serious structural damage. All it takes is one bad leak to cause thousands in repairs, and if moisture continues to creep in over time, it can slowly break down a building from the inside out.
But here’s the thing—moisture doesn’t just come from the usual suspects like leaky roofs or heavy rainstorms. It can also creep in from below, seeping up from the ground and into a building’s crawl space. And because crawl spaces are often out of sight, they’re out of mind—until the damage is already done.
Why Crawl Space Moisture is a Problem
Most of the time, crawl spaces are just there—used for storage or simply ignored. But the problem? Dirt floors are common in crawl spaces, and they’re a prime source of moisture infiltration. If left unaddressed, this moisture can cause a ripple effect of issues:
- Structural damage—moisture weakens wood framing and supports.
- Electrical shorts—high humidity can corrode wires and connections.
- Pipe erosion—constant exposure to damp conditions accelerates wear.
- Insulation degradation—fiberglass and other insulation materials lose effectiveness.
- Poor indoor air quality—mold spores and dust mites thrive in damp environments.
The good news? A crawl space vapor barrier is a simple and effective solution to combat these issues before they start.
What is a Crawl Space Vapor Barrier?
A crawl space vapor barrier is a heavy-duty membrane that prevents moisture from seeping up from the soil. When paired with a comprehensive waterproofing system, you can block both liquid water and water vapor before they ever reach the building.
How Do Vapor Barriers Work?
Think of vapor barriers as a protective shield for your crawl space. These thick plastic sheets are laid across the ground, creating a continuous layer that stops moisture migration. But keep in mind—they only block ground moisture. If there’s runoff or a plumbing leak, you’ll need additional waterproofing measures to keep the space dry.
Do You Really Need a Vapor Barrier?
If you’re building in a dry climate, you might think a vapor barrier isn’t necessary. But don’t be so sure. Even in areas like Arizona, the ground holds surprising amounts of moisture. In fact, a study by Advanced Energy found a 15% annual energy savings in buildings with sealed crawl spaces, proving that controlling moisture also improves efficiency.
Bottom line: if there’s a crawl space, a vapor barrier is worth considering—no matter where you’re building.
How Thick Should the Barrier Be?
The PERMINATOR® underslab vapor barrier comes in 10 and 15-mil thickness options. The choice depends on the level of protection required. Since crawl spaces don’t have the added protection of a concrete slab, durability is key. The standard for plastic vapor retarders is ASTM E1745, and PERMINATOR exceeds those requirements, ensuring you get the best protection possible.
Where to Buy Crawl Space Vapor Barriers
PERMINATOR underslab vapor barriers are available across the U.S. and Canada, as well as other international locations. To find a local distributor, visit our distributor locator.
Prepping Your Crawl Space for Installation
Before installing a vapor barrier, make sure your crawl space is ready:
- Clear out any stored items to get full access to the ground.
- Dry out the space—remove standing water, wet insulation, and debris.
- If mold is present, consider professional remediation.
Once the crawl space is clean and dry, gather your tools:
- PERMINATOR® Vapor Barrier
- PERMINATOR® Tape
- TERMINATION BAR
- PERMINATOR® BUTYL TAPE
- Shovel, utility knife, hammer drill, reciprocating saw
- Measuring tape, screwdrivers, wire staples
- Respirator, vacuum, towels
Installing Your Crawl Space Vapor Barrier
Now that your crawl space is prepped and dry, it’s time to install your vapor barrier. Follow these steps for a clean, effective installation:
- Check Local Building Codes – Before you start, verify the required gap to leave unsealed from the top of the foundation wall (typically 3”).
- Apply PERMINATOR BUTYL TAPE – Run a continuous strip of PERMINATOR BUTYL TAPE around the foundation wall where the vapor barrier will attach.
- Lay Out the PERMINATOR Vapor Barrier – Unroll the PERMINATOR underslab vapor barrier across the crawl space floor, ensuring complete coverage. Extend the material up the foundation walls, pressing it firmly against the BUTYL TAPE you applied earlier.
- Secure the Vapor Barrier with the TERMINATION BAR – Install the TERMINATION BAR over the top of the PERMINATOR barrier at the foundation wall, in line with the BUTYL TAPE, to keep everything locked in place.
- Seal All Seams and Penetrations – Use PERMINATOR Tape to fully seal overlaps, penetrations, and column wraps, ensuring an airtight barrier.
- Adjust for Full Coverage – Make sure the vapor barrier is spread evenly across the crawl space floor and flush against all surfaces.
- Overlap and Seal Seams – Check local building codes for the minimum required overlap. Some may call for at least 6 inches, while others require up to 12 inches. Overlap the seams accordingly and seal them with PERMINATOR Tape to maintain an effective moisture barrier.
Improving Crawl Space Ventilation
PERMINATOR is a top-tier solution for moisture and even soil contaminants like radon. But for maximum effectiveness, consider additional waterproofing strategies:
- Enclose the crawl space to prevent external moisture intrusion.
- Use HVAC-supplied air to quickly evaporate any residual moisture.
- Install a dehumidifier and proper exhaust ventilation.
At the end of the day, protecting your commercial buildings from moisture damage starts from the ground up. A quality vapor barrier like PERMINATOR can make all the difference in extending the lifespan and durability of any structure.
Crawl Space Vapor Barrier Products & Accessories

PERMINATOR
PERMINATOR underslab vapor barrier is a new generation of polyolefin-based resin/chemical technology. PERMINATOR provides the vapor barrier industry with a…

PERMINATOR TAPE
PERMINATOR TAPE is a self-adhesive tape, used in conjunction with the application of PERMINATOR underslab vapor barrier. It is for…

TERMINATION BAR
TERMINATION BAR is a multi-purpose, preformed, professional way to attach a wide variety of construction waterproofing, drainage boards, and flashing…

PERMINATOR BUTYL TAPE
PERMINATOR BUTYL TAPE is a double-sided, reinforced, aggressive, black, butyl rubber tape used in all installations of PERMINATOR EVOH. PERMINATOR…
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