What radon means for a builder
Radon is a naturally occurring radioactive gas that can enter a home from the ground and accumulate indoors. Testing measures the concentration; mitigation changes the building-to-soil pressure path so radon-laden soil gas is collected and exhausted outdoors. (EPA radon risks and solutions)
The health risk is not speculative. EPA calls radon the number-one cause of lung cancer among nonsmokers and the second-leading cause overall, estimating about 21,000 U.S. lung-cancer deaths each year. (EPA health risk of radon) Smoking and radon together create a higher risk, and neither should be treated as background noise.
Use 4 pCi/L as an action threshold, not as a safe-versus-dangerous cliff. EPA’s risk table says to fix a home at 4 pCi/L and to consider fixing between 2 and 4 pCi/L. (EPA health risk of radon) That corrects the tempting but inaccurate shorthand that every result below 4 is simply “routine.” The decision should account for the measured level, test quality, occupancy, and the fact that risk declines rather than vanishes below the action level.
Testing: measure before you prescribe
A radon result is useful only when the test was selected, placed, and handled correctly. EPA says many kits are sold online and in home-improvement stores and directs users to follow the package instructions for placement and return. (EPA radon testing) State radon programs may offer free or discounted kits and can help locate measurement professionals.
For a contractor or builder, the practical testing workflow is:
- Identify the decision. A routine homeowner screen, real-estate transaction, post-construction baseline, and post-mitigation verification may have different timing and professional requirements.
- Use the current instructions. Do not improvise the device location or exposure period. Follow the product protocol and any state real-estate rule.
- Record conditions. Preserve the device ID, room and elevation, start and stop time, weather or unusual building-operation notes, and chain-of-custody details when required.
- Interpret the number correctly. At 4 pCi/L, plan corrective action. Between 2 and 4 pCi/L, EPA says to consider fixing rather than declaring the building risk-free.
- Retest after work. A fan indicator is not a radon result. Confirm performance with a follow-up measurement.
When hiring help, EPA directs consumers to the state radon program for qualified professionals. EPA-funded state programs list providers credentialed through a state process or one of the nationally recognized proficiency programs named on the page. (EPA radon testing) Check the project’s state requirements before assuming a national credential replaces licensing.
Mitigation: collect, exhaust, and verify
What an active mitigation system does
Minnesota’s health department describes the core system clearly: a fan continuously pulls air from the soil and vents it outdoors through a pipe ending above the roof edge. The pipe may run inside or outside but must discharge away from windows and openings. (Minnesota Department of Health)
The collection detail changes with the foundation. Minnesota lists sub-slab suction, drain-tile suction, and sub-membrane systems among the common types. (Minnesota Department of Health)
- Sub-slab suction draws from below a slab.
- Drain-tile suction connects to the drain-tile system and uses sealed sump covers where applicable.
- Sub-membrane depressurization covers exposed crawlspace soil with sealed sheeting and draws from beneath it.
These are not interchangeable details. A professional may perform diagnostics to choose suction points and size the fan for the building. The sump-pump and basement-drainage guide is useful when a drain-tile or sump connection has to be coordinated without compromising drainage.
Sealing supports the pressure system
Foundation cracks and other foundation openings are sealed to limit radon flow and improve system efficiency. (Minnesota Department of Health) Sealing is supporting work, not the complete mechanism: the fan and collection point create the continuous pressure-driven exhaust path. The foundation-waterproofing guide helps distinguish water-control details from radon collection; the two can share penetrations and sequencing without serving the same purpose.
Verify operation and performance separately
A U-tube manometer visually indicates whether the fan is working. (Minnesota Department of Health) It does not report the indoor radon concentration. Minnesota advises a post-mitigation radon test after the new system has operated for at least 24 hours. (Minnesota Department of Health) Closeout should include that result, system labels, operating and maintenance instructions, warranties, and any required permit or inspection record.
Radon-resistant new construction
Radon-resistant new construction is easier to coordinate before the slab and finishes close access. EPA identifies five basic features:
- a gas-permeable layer, commonly clean coarse gravel or an allowed alternative, beneath the slab;
- heavy-duty plastic sheeting or another vapor retarder above that layer;
- a labeled solid PVC vent pipe from below the slab through the conditioned space and roof;
- sealing at foundation-floor and wall openings; and
- an attic junction box for a future vent fan if post-construction testing shows a stronger system is needed. (EPA radon-resistant construction)
EPA says the vent pipe should run through the conditioned space and roof to discharge soil gases outside above the house. (EPA radon-resistant construction) This pipe is not an attic-ventilation component. Keep it distinct from soffit, ridge, gable, and powered attic-ventilation paths; the attic-ventilation guide explains what those systems are designed to do.
The attic electrical provision does not mean every passive stack needs a fan immediately. Test after occupancy or completion under the applicable protocol, then activate the rough-in when the measured result calls for it. Also check adopted codes and state requirements: EPA’s details are a national technical reference, while enforceable construction and professional rules remain jurisdiction-specific.
Radon testing and mitigation FAQ
What radon level should be fixed?
EPA says to fix at 4 pCi/L and to consider fixing between 2 and 4 pCi/L. Four is an action threshold, not a zero-risk line.
Is a short-term store-bought kit acceptable?
EPA says many kits are available online and in home-improvement stores. Follow the package instructions for placement and return, and check whether your state or real-estate transaction requires a professional or specific protocol.
Does sealing foundation cracks solve radon by itself?
Sealing can reduce leakage and improve mitigation efficiency, but an active soil-depressurization system relies on a fan and collection point to pull soil gas and exhaust it outdoors.
What does the U-tube manometer prove?
It visually indicates that the fan is creating a pressure difference. It does not measure the indoor radon concentration, so verify performance with a post-mitigation radon test.
Where does a radon fan exhaust?
A common mitigation layout runs the discharge pipe outdoors above the roof edge and away from windows and openings. Exact termination rules depend on the applicable standard and jurisdiction.
What should be installed for radon-resistant new construction?
EPA’s basic package includes a gas-permeable layer, vapor retarder, labeled vent pipe through the roof, sealed openings, and an attic electrical junction box for a future fan.