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Building a new home?

New homes can be built with a radon reduction system already installed. This is called Radon Resistant New Construction (RRNC). The most common RRNC method is to install a passive radon reduction system. Typically, passive radon reduction systems are very similar to mitigation systems described within this document, but do not have a fan installed. Adding radon-resistant features to a new home while it is under construction is generally much cheaper than installing a mitigation system after the home is built. Passive radon reduction systems can also be incorporated into the building design and hidden from view, making the home more aesthetically pleasing.

Just because a house is built radon resistant does not mean radon levels could not become elevated. It is suggested that a test be performed every two years to ensure concentrations are maintained at a low level. If the passive RRNC features do not reduce the radon concentrations below 4 pCi/L, a fan can easily be added to the existing system at relatively inexpensive cost. For more information on RRNC please visit:

While the techniques may vary for different house foundations and building site requirements, the five basic features that builders should include to prevent radon from entering a home are:

  1. Gravel: Use a 4-inch layer of clean, coarse gravel below the “slab,” also called the foundation. This layer of gravel allows the soil gases, which includes radon, that occur naturally in the soil to move freely underneath the house. Builders call this the “air flow layer” or “gas permeable layer” because the loose gravel allows the gases to circulate. NOTE: In some regions of the country, gravel may be too expensive or unnecessary. Alternatives are allowed, such as a perforated pipe or a collection mat.
  2. Plastic Sheeting or Vapor Retarder: Place heavy duty plastic sheeting (6 mil. polyethylene) or a vapor retarder on top of the gravel to prevent the soil gases from entering the house. The sheeting also keeps the concrete from clogging the gravel layer when the slab is poured.
  3. A Vent Pipe: Run a 3-inch or 4-inch solid PVC Schedule 40 pipe, like the ones commonly used for plumbing, vertically from the gravel layer (stubbed up when the slab is poured) through the house’s conditioned space and roof to safely vent radon and other soil gases outside above the house. (Although serving a different purpose, this vent pipe is similar to the drain waste vent, DWV, installed by the plumber.) This pipe should be labeled “Radon System.” Your plumber or a certified radon professional can do this. For more information visit:
  4. Sealing and Caulking: Seal all openings, cracks, and crevices in the concrete foundation floor (including the slab perimeter crack) and walls with polyurethane caulk to prevent radon and other soil gases from entering the home.
  5. Junction Box: Install an electrical junction box (outlet) in the attic for use with a vent fan, should, after testing for radon, a more robust system be needed.
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