Radon-Resistant Construction Requirements

Washtenaw County enforces Appendix F of the 2015 Michigan Residential Building Code. This appendix requires residential construction projects to be built using methods that limit the entry of radon gas into the structure.

Why is this required in Washtenaw County?

In the 1990s, the EPA and other federal and state agencies conducted studies on radon potential across the United States. These studies looked at test results of indoor air in homes, soil studies, and geologic formations. The EPA developed a county-by-county map that indicated the potential for radon to be found in homes and other buildings. In Michigan, nine counties were categorized as "Zone 1," meaning that radon is more likely to be elevated in these areas. The Zone 1 counties include Branch, Calhoun, Cass, Hillsdale, Jackson, Kalamazoo, Lenawee, St. Joseph, and Washtenaw. 

What does "radon resistant" mean?

Building a home to be radon resistant means using methods that limit the entry of radon gas into the living spaces of the structure. This is considered a "passive" system, since no fans or electricity is needed to operate the system, as it relies on the natural upward flow of air to exhaust the radon. The main components of a typical passive radon system include the following features. Please review Appendix F of the 2015 Michigan Residential Building Code for full details and requirement, including requirements for homes with soil floor crawl spaces.

  • Gas permeable material must be placed under the concrete slab, which could be a minimum of 4 inches of clean aggregate, or a minimum of 4 inches of sand or native fill under a layer of soil gas collection matting.
  • Soil-gas retarder must be placed on top of the gas-permeable layer, before pouring the slab or placing the floor assembly. The soil-gas retarder must be at least 6-mil (0.15 mm) thick polyethylene or equivalent, must cover entire subfloor areas,and sheets must overlap by at least 12 inches. 
  • Vent pipe must be a minimum of 3 inches in diameter PVC that is embedded vertically into the sub slab aggregate before the slab is poured, or inserted into an interior perimeter tile loop, or through a sealed sump cover. Vent pipe must extend through the conditioned space of the building and extend 12 inches above the surface of the roof, exhausting at least 10 feet away from any window and door openings. Vent pipe must be labeled "Radon Reduction System."
  • Seal concrete joints, openings around pipes and wires, and any other objects that penetrate the concrete slab. Sumps must be covered with a gasketed or sealed lid.
  • Power source and access must be located in the attic near the anticipated location of a future radon fan, if needed.

See drawings of different foundation types with these features.

Radon in Washtenaw County

Radon is a tasteless, colorless, odorless gas that can seep into homes through cracks in the foundation, sump pump crocks, hollow block walls, or other openings. Long-term exposure to radon is the second-leading cause of lung cancer in the United States. Washtenaw County has been designated a "Zone 1 County," meaning homes built here have the highest potential for elevated radon levels due to the County's geology and soil composition.

Appendix F requirements have been shown to help lower indoor radon levels, protecting the public from exposure to this potentially deadly gas.

Radon-Resistant Construction