Q & A Under slab Vapor Barriers For Commercial Buildings and Homes

Question:  If the soil is dry, is it necessary to put an under slab 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: What is radon, and why is it a concern in homes?

Answer:  Radon is a radioactive gas that can seep into homes from the ground. It's colorless, odorless, and tasteless, making it imperceptible. Prolonged exposure to high radon levels can pose health risks, including an increased risk of lung cancer.

Question : How does radon enter homes, and why is the under-slab area significant?

Answer: Radon is produced naturally in the soil and can enter homes through cracks or openings in the foundation. The under-slab area is crucial because it provides a direct pathway for radon to infiltrate indoor spaces. Installing a vapor barrier in this area helps mitigate radon intrusion.

Question: What is the purpose of an under-slab vapor barrier in radon mitigation?

Answer: An under-slab vapor barrier acts as a protective barrier between the soil and the indoor environment. It helps prevent the upward movement of radon gas, reducing its entry into the home. Additionally, it aids in controlling moisture, which can contribute to other issues like mold growth.

Question: Can any type of plastic sheeting be used as an under-slab vapor barrier for radon mitigation?


Answer:  Not all plastic sheeting is suitable for radon mitigation. It's essential to use a specifically designed radon barrier, typically made of high-density polyethylene (HDPE) or other materials that resist radon gas penetration. These barriers are engineered to meet specific standards for radon resistance.

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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