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Thinking About A Crawl Space Vapor Barrier? Read This First.

Crawl Space
Crawl Space

Crawl Space Moisture Isn’t Harmless

Are you thinking about installing a crawl space vapor barrier? If so, you’ve landed on the right page. We’re going to talk about the definition of a crawl space vapor barrier, why you might – or might not – need one, the difference between a vapor barrier and crawl space encapsulation and other ways you can keep moisture out of your crawl space.

Moisture in your home’s crawl space isn’t harmless. It can negatively affect both your physical health and your home’s structural integrity.

Crawl space moisture comes mainly from the ground, and if it isn’t controlled, it will rot wood beams and joists and contribute to the growth of mold and mildew. Wood rot can, of course, compromise the structural integrity of your home. However, most homeowners don’t know that a certain percentage of crawl space air makes its way into the home’s living area. If this air is full of mold and other allergens because the crawl space is damp, the air quality inside the home will suffer.

Crawl space humidity also contributes to higher humidity in the home’s living area, which means higher heating and cooling costs. Therefore, getting the moisture in the crawl space under control is essential if you want a healthy, energy-efficient home.

For more information see The Importance Of Proper Foundation Drainage Around Your Home.


What Is A Crawl Space Vapor Barrier?

You can think of a crawl space vapor barrier as a big plastic sheet placed on the crawl space floor to prevent moisture in the soil from getting into the crawl space. (Vapor barriers are also used to control moisture in basements, walls, and other areas.)

Crawl space vapor barriers are also called vapor diffusion retarders or just vapor retarders. The term “retarder” refers to the fact that they slow down the ability of water vapor to pass through a material. They’re rated in units of permeability called “perms.” The International Residential Code lists three classes of vapor barrier:

Class 1 materials like glass and sheet metal. These are impermeable.
Class 2 materials such as plywood and polystyrene. These are semi-impermeable.
Class 3 materials include gypsum board, unfaced fiberglass insulation, and brick. These are semi-permeable.
Crawl space vapor barriers come in two varieties: membrane or coating. Membranes are usually thin, flexible, and come in rolls. An example of a crawl space membrane vapor barrier is polyethylene sheeting. Thicker membranes are also available.

Vapor barriers must be installed correctly if they’re going to be effective. They need to be sealed without gaps or openings that could allow moisture from the soil to escape into the crawl space.

Note: A crawl space vapor barrier prevents vapor, not water, from entering your crawl space. Water can get into a crawl space from elsewhere. Examples include water intrusion from a high water table, clogged gutters, improper grading around the home, leaky pipes (water or drain), etc. If there’s a problem with these, installing a crawl space vapor barrier is rather pointless. On the other hand, if these problems are fixed, a vapor barrier helps a lot.

Crawl Space Encapsulation Vs A Vapor Barrier

Encapsulation is when we wrap a vapor barrier around the inside of a crawl space. A vapor barrier is the material we use to encapsulate a crawl space.

As we noted above, a crawl space vapor barrier prevents moisture in the soil from entering the crawl space. However, if there’s excess water in the ground to begin with, that needs to be addressed via waterproofing with a drain tile system.

A drain tile system will channel excess water in the soil away from the foundation, and encapsulation, which covers the crawl space walls and floor, ensures that the air stays clean and dry. The bonus is the fact that you can use an encapsulated crawl space for storage.

Waterproofing and encapsulation is the best way to protect the crawl space and ensure that the air entering the home is clean and dry. In other words, the two should be used together.

Do You Need A Crawl Space Vapor Barrier?

Not necessarily. It depends on the climate where you live and how your home is constructed. There are a couple of reasons you might want to install one though:

You’re having problems with high humidity and mold growth in your crawl space.
You want to create additional storage space. In this case, encapsulation (covering the crawl space floor and walls with a vapor barrier ) along with a drain tile system and a dehumidifier is the way to go.

Other Ways To Keep Moisture Out Of Your Crawl Space

other ways to keep moisture out of your crawl space

Getting groundwater under control is the best way to keep water out of a crawl space or basement. Here are some methods for doing that:

Regrade your yard, if necessary – Your yard should slope away from the foundation. If it doesn’t, water will pool around the foundation and get into the crawl space. If you’re not up to doing this job yourself, a landscaper or foundation repair contractor can help you out.

Clean your gutters regularly – If your home’s gutters are clogged, water will spill over the side of the house and into the soil around the foundation. This is where you don’t want it.

Install downspout extensions, if necessary – Sometimes, downspouts are too short and release water next to the foundation where it sinks into the soil. Downspout extensions are inexpensive, easy to install, and will channel water away from the foundation before releasing it.

Install a drain tile system – When it comes to waterproofing, a drain tile system is a gold standard. Unlike other waterproofing solutions, a drain tile system doesn’t simply create a barrier to prevent water from entering the crawl space. Instead, it removes excess moisture in the soil. If the water isn’t there to begin with, it can’t get into your crawl space.

A crawl space vapor barrier can go a long way toward making your home healthier and more comfortable, provided you don’t have any unaddressed drainage issues. If you’re thinking about a crawl space vapor barrier and you’re in our service area in Nebraska, Iowa, Kansas, and Missouri, contact us today for a repair estimate.


Dave Epp

Dave is the President at Epp Foundation Repair with over 27 years of experience in the industry. Dave has worked on thousands of foundation, basement, concrete, and crawl space repair projects since 1993. Dave is involved in several civic and church organizations and enjoys coaching youth sports, mainly football, golfing, and elk hunting.



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