Radon-resistant new construction means building a home with features that help keep radon out and make it easy to lower radon later if needed. All the materials are commonly used in home construction, and no special skills are required (EPA). There’s no reliable way to test the ground for radon in advance (Pennsylvania DEP), so these features are installed before anyone knows what the level will be.
Every new home should still be tested after you move in, even if it was built radon-resistant (EPA, Citizen’s Guide).
The five features
| Feature | What it does |
|---|---|
| Gas-permeable layer | Usually 4 inches of clean, coarse gravel under the slab, so soil gas can move freely beneath the house. Perforated pipe or a collection mat may be used instead in some regions. |
| Plastic sheeting or vapor retarder | Heavy-duty sheeting on top of the gravel helps keep soil gas out, and keeps wet concrete from clogging the gravel. |
| Vent pipe | A 3-inch or 4-inch solid PVC pipe runs from the gravel layer through the house and roof to vent soil gas outside. It should be labeled “Radon System”. |
| Sealing and caulking | Openings, cracks and crevices in the foundation floor and walls are sealed, including the crack around the slab edge. |
| Junction box | An electrical box in the attic is ready to power a fan if a test later shows you need one. |
From EPA. Details vary by foundation. In a crawl space, for example, there’s no gravel layer, and sheeting with sealed seams goes directly over the crawl space floor. EPA also says a second junction box belongs in the living space, to power the alarm that’s installed with a fan (EPA, Home Buyer’s and Seller’s Guide).
What is a passive radon system?
A passive system is these same features with no fan. It relies on the natural upward flow of air to carry radon out through the pipe (Oakland County, Michigan). An active system adds a fan to the pipe, which lowers radon further.
Don’t assume a passive system has solved the problem. Michigan says one typically reduces radon by about 50% (Michigan EGLE), and WHO says passive systems can reduce indoor levels by more than 50%, with fans reducing them further (WHO). So a home with a high starting level can still test high with a passive system in place.
What it costs
Michigan estimates the average cost of installing a passive system at $350 to $500 (Michigan EGLE). EPA says the builder’s cost can vary widely, but is typically less than the cost of mitigating the home after construction (EPA). For comparison, see what radon mitigation costs in an existing home.
Building the pipe in during construction also keeps it inside the house. Without one, a high test later may mean a system on the outside of the home (Pennsylvania DEP).
EPA also says these features, installed properly and completely, may help lower moisture levels and can make a home more energy efficient (EPA, Home Buyer’s and Seller’s Guide).
After you move in: test, and add a fan if needed
- Test as soon as possible after you move in (EPA, Home Buyer’s and Seller’s Guide). See how to test for radon.
- If the result is 4 pCi/L or more, have a qualified mitigator add a vent fan, which makes the system active (EPA, Citizen’s Guide). See how radon fans work.
- Test again after the fan goes in, to confirm it’s working and that levels are below 4 pCi/L (Boulder County, Colorado).
Is it required where you’re building?
Building codes in your state or local area may require these features (EPA, Citizen’s Guide), and the rules vary a lot. Three examples, which aren’t a full list:
- Michigan: required in nine counties: Branch, Calhoun, Cass, Hillsdale, Jackson, Kalamazoo, Lenawee, St. Joseph and Washtenaw. The state recommends the techniques for all homes statewide (Michigan EGLE).
- Massachusetts: homes built after January 2015 in Worcester, Middlesex and Essex counties must have these features under the state building code (Massachusetts DPH).
- Nebraska: a law effective in September 2019 requires a passive system in new homes and new commercial buildings, enforced by local governments whose building codes adopt or generally conform to the state code (Nebraska DHHS).
Where it isn’t required, EPA still recommends these features for new homes in high radon potential (Zone 1) areas (EPA, Citizen’s Guide), and you can ask your builder to include them (EPA). Your state radon program or local building department can tell you what applies.
What to ask your builder
- Is the home radon-resistant? Ask whether they follow a recognized approach. EPA gives International Residential Code Appendix F, ASTM E 1465-08 and ANSI/AARST RRNC 2.0 as examples (EPA, Home Buyer’s and Seller’s Guide).
- Does it have all five features? Use the table above as a checklist.
- Where does the pipe run? It should go from under the slab through the house and roof, and be labeled.
- Is a junction box in place in the attic? That makes adding a fan easier.
- Has it been tested? If the home is already occupied, ask for the result, and test it yourself after you move in. See radon inspections.
Radon is found in new homes as well as old ones (EPA, Citizen’s Guide), so a new build isn’t a reason to skip the test. Already living in your home? See how radon mitigation systems work.