Underslab Vapor Barriers For Commercial Buildings

Question:  If the soil is dry, is it necessary to put an underslab vapor barrier?

Answer:  Many builders believe a moisture barrier should be put down in every instance.  Concrete does a terrific job of pulling water from the soil below it through capillary action.  This will result in the building having a dampness inside. 

Question:  Are there other reasons to put down a vapor barrier beside blocking water transmission?

Answer:  In some parts of the country, radon is a much bigger problem than water.  Radon is an odorless, highly poisonous gas that can penetrate concrete.  Radon comes from the underground uranium deposits that are deep in the ground. In a commercial building that is virtually air tight, a vapor barrier that is engineered to block radon is a must!

Question:  Why do professionals state that a thicker vapor barrier is worth the added dollars compared to a thinner vapor barrier?

Answer:  Radon causes cancer and is a radio-active gas!  This is not the place to cut corners.  It's important that the liner withstand construction traffic and not be susceptible to any tears or pinholes. Pump hoses, reinforcing bar placement and other hazards can rip thinner liners.  Even though the EPA and ASTM have at one time claimed that 6-mil polyethylene sheets are adequate, but over time the industry has determined that 6 mil is not acceptable as an underslab gas barrier.

ASTM E 1745-09 "Standard Specification for Plastic Water Vapor Retarders Used in Contact with Soil or Granular Fill under Concrete Slabs" can be used as a starting point. This standard requires tensile strength of no less than 45.0 lb/in. and a puncture resistance of 2200 grams. To meet these requirements, most barriers are at least 10 mils thick and made with state-of-the-art resins to provide exceptional puncture strength. To learn more about what makes a liner "state-of-the-art" click here.

General facts about Radon

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