Idaho Radon Zones and Risk Levels
The EPA classifies Idaho counties into three radon zones based on predicted indoor radon levels. Most of Eastern Idaho falls in Zone 1, the highest risk category with predicted levels above 4 pCi/L (the EPA action level). This does not mean every home has dangerous radon — it means testing is essential because the probability is high.
| County | EPA Zone | Risk Level | Major City |
|---|---|---|---|
| Bonneville | Zone 1 | High | Idaho Falls |
| Madison | Zone 1 | High | Rexburg |
| Bannock | Zone 1 | High | Pocatello |
| Bingham | Zone 1 | High | Blackfoot |
| Jefferson | Zone 1 | High | Rigby |
| Fremont | Zone 1 | High | St. Anthony |
| Blaine | Zone 1 | High | Sun Valley |
| Twin Falls | Zone 2 | Moderate | Twin Falls |
Radon levels can vary dramatically between neighboring homes due to differences in soil composition, foundation construction, and ventilation. The only way to know your home's radon level is to test it. Do not assume your home is safe because a neighbor tested low.
Testing Methods
Radon testing is simple, affordable, and should be done before any basement finishing work begins. There are three main testing approaches.
Short-Term DIY Kit
$15–$30 · 2-7 days
Accuracy: Moderate
Charcoal canister or alpha track detector placed in the basement. Mail to a lab for results. Good for initial screening.
Long-Term DIY Kit
$25–$50 · 90+ days
Accuracy: High
Alpha track detector left in place for 3-12 months. Provides the most accurate annual average. Best for decision-making.
Professional Test
$150–$300 · 48 hours
Accuracy: Very High
Continuous radon monitor (CRM) placed by a certified tester. Hourly readings detect tampering and provide detailed data.
For basement finishing projects, we recommend a professional test or a short-term DIY test followed by a long-term test. Place the test in the lowest livable area of the basement, away from windows, doors, and exterior walls, at least 20 inches off the floor. Keep windows and doors closed (except for normal entry/exit) for 12 hours before and during the test.
Mitigation Systems
If your radon test shows levels at or above 4 pCi/L, the EPA recommends mitigation. The most common and effective method is sub-slab depressurization (SSD), which creates negative pressure beneath the foundation slab to prevent radon from entering the home.
An SSD system works by drilling a 4-inch hole through the basement slab, inserting a PVC pipe, running it up through the house and out the roof, and attaching a continuously running radon fan. The fan creates suction that draws radon from beneath the slab and vents it harmlessly above the roofline. A properly installed system reduces radon levels by 80 to 99 percent.
Install during finishing, not after. If you are finishing your basement and need mitigation, installing the system during construction is significantly easier and cheaper. The PVC pipe can be routed inside a wall cavity, the slab penetration can be hidden, and the system integrates cleanly with the finished space. Retrofitting after finishing means exposed pipes or cutting into finished walls.
Mitigation cost in Idaho: $800 to $1,500 installed. This is a one-time cost, and the system runs continuously with minimal maintenance (fan replacement every 5-10 years, about $100-$200). This is a small price for peace of mind, and many Idaho real estate transactions now require radon testing and disclosure. See our waterproofing guide for related sub-slab systems.
Radon FAQ
Does Idaho have high radon levels?
Yes. Much of Idaho, particularly Eastern Idaho, falls in EPA Zone 1 (highest radon potential) with predicted average indoor levels above 4 pCi/L. Bonneville County (Idaho Falls), Madison County (Rexburg), Bannock County (Pocatello), and Bingham County (Blackfoot) all have elevated radon risk. Testing is the only way to know your specific home's levels.
How much does radon testing cost?
A DIY short-term test kit costs $15 to $30 (available at hardware stores or free from some county health departments). A professional radon test costs $150 to $300 and provides more accurate results with calibrated equipment and proper protocols. Long-term test kits (90+ days) cost $25 to $50 and give the most accurate annual average.
How much does radon mitigation cost?
A standard sub-slab depressurization system — the most common mitigation method — costs $800 to $1,500 installed in Idaho. This includes drilling through the slab, installing a PVC vent pipe through the roof, and adding a radon fan. The system runs continuously and typically reduces radon levels by 80-99%. Annual electricity cost for the fan is about $50-$75.
Should I test for radon before finishing my basement?
Absolutely. Testing before finishing is critical because mitigation is far cheaper and easier to install before walls and ceilings are completed. If radon levels are above 4 pCi/L, install a mitigation system during the finishing process — the piping can be hidden inside walls, and the system integrates seamlessly with the finished space.
Does finishing a basement affect radon levels?
Finishing a basement can either increase or decrease radon depending on how it is done. Sealing the floor with a vapor barrier and covering cracks reduces radon entry points. However, spending more time in the basement increases exposure. A sub-slab depressurization system provides active, reliable radon reduction regardless of finishing details.
Related Guides
Making your whole property healthy? Visit Idaho Sprinkler Systems and Idaho Yard Pros for outdoor improvements.