How To Install Vapor Barrier In Crawl Space

Follow our DIY guide to installing vapor barrier in your home’s crawl space.

Required Tools And Materials

These tools are necessary for any DIY vapor barrier projects:

• Hammer.
• Utility knife.
• Caulk gun.
• Straightedge.
• Tape measure.

Have the following materials ready ahead of time:

• Caulk.
• Tape.
• Rigid insulation.
• 6-mil plastic.
• 1-1/2 in. rigid insulation.
• Landscape fabric stakes.
• Treated 1x4s.

Steps To Install A Polyethylene Vapor Barrier

Water collecting on pipes and concrete walls in a crawl space is an all-too-common issue for homeowners. Ventilation openings were designed to flush out moisture, but they struggle to do the job effectively in non-dry climates. Humid air carries moisture which condenses on cool walls, pipes, and the underside of flooring.

The best solution to this issue is to close up the vents with polyethylene vapor barrier. Make sure you get approval from your local building inspector before performing this task. Follow these steps below.

Step 1

• Make sure to create good drainage around your house to keep any rainwater from flowing in underneath the foundation.
• The best way to reduce crawl space moisture is to slop the soil away from your home at about 1/2 in. per foot.

Step 2

• Cover the dirt crawl space using a plastic moisture polyethylene vapor barrier.
• Overlap any seams by taping them.
• Bring the plastic approximately 6 in. up the wall and fasten it.
• Stake the plastic down using landscape fabric stakes to keep it in place.

Step 3

• Cover any exposed foundations walls with 1-1/2 in. of rigid, moisture-proof insulation at this time.
• This will not only insulate the walls, but it will also keep any dampness in the concrete from infiltrating the crawl space.
• Other types of vapor barriers (alternatives to polyethylene) can require drywall covering.

Step 4

• Insulate your rim joists.
• It’s recommended to use rigid insulation and caulk it in place to prevent any air leaks.

Step 5

• Cap the foundation wall interior with a 6-mil layer of plastic and galvanized flashing to serve as a termite barrier and prevent moisture buildup.
• Building codes may include different details for termite control based on your location.

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