What is a Vapor Barrier? What does a Moisture Barrier do? 

A vapor barrier is a building material also called a vapor retarder whose function is to retard water vapor that can come through the floor, walls, or ceiling. It therefore resists moisture movement at a lever that sufficiently complies with a specific building code. Plastic sheeting or foil will regulate the flow of water from crossing the moisture/vapor barrier.  Crawl space vapor barriers are often used in basements to retard the moisture from coming up into the basement. 

Do moisture barriers STOP all moisture from coming through the barrier? No. Very few materials can accomplish this.

Where should a vapor barrier be placed?

A moisture retarder should be placed anywhere moisture can enter a wall, floor or ceiling and thus cause damage. Moisture can seep up through concrete foundations from the earth below.

Do I really need a Moisture Barrier?

The problem with moisture entering your home is bigger than it seems on the onset. Water over time can cause structural damage to the home's structure and cause health problems for the residents. The crawl space under you home comes in contact with the ground thus allowing moisture into that area. Little by little, mold and mildew accumulate which can cause asthma or allergies. In some cases rats, mice and other critters may seek refuge and be drawn to the water.

Can You Use 4 mil Plastic for a Vapor Barrier?

NO. In our professional opinion, if you are serious about stopping the moisture from entering your structure you need to use a proven product that is engineered for this purpose. Don't take our word for it, check with your local building codes, the International Building Codes, or the U.S. Department of Energy.

The way to select a vapor retarder is based on its perm rating.  A perm rating is a unit that indicated the mass rate of water vapor flowing through one square foot of material. Put another way, a perm measures the relative ease in which moisture or water vapor will pass through material.  In the United States, one perm is 1 grain of water vapor per hour, per square foot of mercury.  The 4 mil polyethylene sheeting does not have a perm rating.

What's better a smaller perm rating or  larger perm rating?

The lower the perm number the greater the material's resistance to moisture movement.  And the winner is....

Vapor barriers with a perm rating of less than 1 make good vapor barriers.

IBC International Building Code & IRC International Residential Code Vapor Retarder Specifications

Vapor retarder class shall be defined using the desiccant method* of ASTM E 96 as follows:

• Class I vapor retarder: 0.1 perm or less.
• Class II vapor retarder: 0.1 < perm <1.0 perm.
• Class III vapor retarder: 1.0 < perm <10 perm.

Don't forget to consider your climate! 

Below are some vapor barrier for your consideration.

• Poly Scrim Crawl Space Vapor Barrier:  String reinforced Crawl Space Liners
• Enkavent 6128- Radon Control
• Crawlspace 2000 : A white 20 mil string reinforced liner  12' x 100'
• Poly Scrim 12 Antimicrobial: 12 mil liner  12' x 100'

Recommended Tapes:

• • Ultra Perm Tape:  Exceptionally aggressive all weather tape
  • Butyl Seal Tape-Double Sided Tape Used to attach the plastic to the foundation walls of  the crawl space.
  • Vapor Seaming Tape Used to seam the vapor barrier plastic together in the crawl space. Minimum overlap of 6 inches.