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Crawl Spaces

Crawl spaces can be a major source of radon entry.

If your home has a crawl space and the floor is concrete, the crawl space is treated much like the basement floor would be.  Large cracks and opening would be sealed.

If the floor of your crawl is dirt or gravel and is accessible, then the floor is covered and sealed to block radon entry.

In Illinois when covering a crawl space floor, a minimum of 6 mil or 3 mil cross laminate polyethylene must be used.  At VSI we use 3.5 mil cross laminate because of the added strength over single polyethylene as shown below.  You can also use your crawl space for storage after we have sealed it, just be careful when storing objects with sharp edges.

Material Tensile
-Strength (PSI)
force (lb)
3.5 mil cross
7250 15.3
6 mil Poly 2705 6.4
10 mil Poly 2215 8.1


Plastic is laid out over the crawl space floor.

1″ by 3″ furring strips are used to attach plastic to walls, this gives a permanent physical attachment and helps prevent plastic from falling off or being torn off the wall.

Caulk is then applied to the top seam to make an air tight seal.

Seams in the plastic are overlapped and sealed.
Plastic can be laid out black or white side up.