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Radon Resistant Construction

Building radon resistance is cheaper

Building radon resistance into a new house is far less costly than radon mitigation after construction. The passive system outlined below is 50%–70% of the cost of a retrofitted radon mitigation system, which is about $1,200 to install and can have significant operating costs.

If indoor radon is elevated, a fan-powered mitigation system (the only thing that will work as a retrofit) can cause withdrawal of conditioned air via cracks and openings through the slab behind finished walls. The energy for the fan, plus heating of the cold outdoor air infiltrating to replace air withdrawn from the home, can cost $200 per year in northern climates.

Studies across the country and in Wisconsin show that passive stacks in properly built and sealed new construction typically reduce the radon in indoor air by 50%, compared to the radon measured with the stacks capped.

Check out Slipstream to learn best practices in radon controls for new homes

Environment Protection Agency's (EPA) five features

EPA lists five features to be installed as new construction is built to constitute a proper system for controlling radon. Although techniques and materials may vary, these are features that builders should include to prevent radon from entering new homes.

  1. Gravel: Use a 4-inch layer of clean, coarse gravel below the “slab,” also called the "foundation." This layer of gravel allows naturally occurring soil gases, which include radon, 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.
  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.
  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.

Other standards

Additional resources

Check radon levels after home is completed

Since the radon in a home may still be elevated despite these precautions (although it is significantly less likely), a radon measurement is needed after the home is finished. If the radon is elevated, installing a fan in the stack, in space originally provided for it in the attic, ensures adequate control at a low additional cost. The fan must not be located in conditioned air; for example, not in the basement.

Workers doing this work must understand that the stack goes through a heated, interior partition, that space for installing a fan must be left in the attic, and that sealing of the floor-wall joints must be done before any finished basement walls are installed.

Last revised April 7, 2023