A vapor barrier (also called a vapor retarder) is required by the International Residential Code (IRC R506.2.3) and the Residential Edition of the Florida Building Code for concrete floor slabs on grade at the heated areas of a home. It is not required at driveways, patios, and other areas that are not likely to be enclosed in the future. But a vapor barrier is required under the floor slab of an attached garage because it has the potential for conversion to living space. See our article Where is a 6-mil polyethylene (Visqueen) vapor retarder not required under a concrete floor slab on grade? for a full list. 

    The vapor barrier is necessary because, contrary to what the average person thinks, concrete itself is not a waterproof material. Water can move upward through a concrete slab by capillary action, the same way that a sponge will suck water up out of a puddle, just much slower. 

    For more on this subject, see our articles Why does my concrete floor slab sweat and get slippery? 

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Here’s links to a collection of some of our other blog posts about CONCRETE:

• How can I tell if cracks in the garage floor are a problem or not?

• Why is the concrete window sill cracking?

• There's cracks running along the home's concrete tie beam. What's wrong?  

• What is fiber reinforced concrete? 

• What is concrete spalling?  

• Why is there a "WARNING! POST-TENSION SLAB" sticker in my house?

• How can I identify a home as ICF (Insulated Concrete Form) construction?

• How can I tell if cracks in the wall or floor are getting worse or staying the same?

• What does concrete spalling look like?

• What is the average life expectancy of a concrete driveway? 

• What is the average life expectancy of a concete walkway?

• How does concrete spalling cause structural failure if not repaired?

• What is the difference between a control joint and an expansion joint?

• What causes honeycomb in concrete? 

• Why does concrete shrink as it sets and hardens?

    Visit our CONCRETE AND CONCRETE BLOCK page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.