How to Install a Vapor Retarder in a Crawl Space

If you live in an older home with a crawl space and dirt floor beneath the house, you can benefit from installing a vapor retarder. This device reduces moisture buildup in crawl spaces, reducing or preventing damage to the wood understructure of your house.

Things You'll Need

• Shovel
• Polyethylene sheets
• Tape
• Pressure-treated furring strips and masonry nails
• Sand or concrete

Instructions

1. Check local building codes regarding crawl spaces. Meet all codes in regards to materials you're using to install a vapor retarder in the crawl space.

2. Dig a trench 2-inches deep around the perimeter of the crawl space. Lay down vapor retarder or sheets of polyethylene film, overlapping them at least 2 feet. Extend the edges of the sheets at least 12 inches on all 4 sides.

3. Cut sheets around any fixed objects in the crawl space such as floor beam supports. Tape all seams and around cut spaces. Fill in trench with soil that you removed to hold down vapor retarder.

4. Hold up excess edges against crawl space walls by using tape or furring strips made with pressure-treated wood nailed with masonry nails to the walls. Make sure vapor retarder extends above grade level.

5. Cover vapor retarder with a thin layer of sand, or pour a thin layer of concrete. This helps keep the plastic sheets from getting damaged when you walk on them.

Tips & Warnings

• You can make small holes in the sheets to help drain any water that might result from flooding or a burst or leaky pipe.

• Make sure you are meeting code requirements for headroom, if you are pouring a concrete slab.

• Don't cover vapor retarder with gravel or anything that can puncture the sheets.