How to Install a Construction Slab Vapor Barrier

Vapor barriers are placed on top of the ground before a concrete slab is poured to prevent moisture from the ground passing into the bottom of the slab and exiting from the top of the slab, damaging flooring and creating humidity problems in a building. They are used under house and building foundation slabs, as well under concrete sidewalks. These barriers are an effective, quick and inexpensive way to safeguard against water vapor problems in the future. The most commonly used vapor barriers are rolls of 6-millimeter-thick plastic sheeting, also known as "6 mil."

Things You'll Need

• Termite treatment
• Tape measure
• 6 mil plastic sheeting
• Utility knife

Instructions

1. Hire a termite treatment company to treat the soil under the slab for termites before installing the plastic.

2. Measure the length and width of the slab, and multiply the two to determine the square footage of plastic sheeting needed. Add 10 percent for waste and overlap.

3. Starting in one corner of the slab, roll out the vapor barrier all the way to the other end.

4. Cut the sheeting off when you reach the other end. Start a new row, overlapping the previous row by 3 inches.

5. Continue laying rows of sheeting until you cover the area of the slab. Any excess sheeting on the last row can be cut off or folded over into the area of the slab.

Tips & Warnings

• If a roll of sheeting runs out in the middle of a row, simply start a new roll and finish the row. Overlap the ends by 3 inches, just like with the sides.