Radon Testing and Mitigation Guide for Homeowners

What Is Radon

Radon is a naturally occurring radioactive gas produced by the decay of uranium in soil and rock. It is colorless, odorless, and tasteless. Radon enters homes through cracks in the foundation, gaps around pipes, and porous concrete. It is the #1 cause of lung cancer among non-smokers and the #2 cause overall (after smoking). The EPA estimates radon causes 21,000 lung cancer deaths per year in the US. Every home should be tested — radon levels vary house to house, even on the same street. The only way to know is to test.

Radon Levels

Radon is measured in picocuries per liter (pCi/L). EPA action level: 4.0 pCi/L (mitigate at or above this level). WHO recommends action at 2.7 pCi/L. Average indoor level in the US: 1.3 pCi/L. Average outdoor level: 0.4 pCi/L. There is no safe level of radon (any exposure increases risk), but practical mitigation targets reducing levels to below 2.0 pCi/L. Approximately 1 in 15 US homes has elevated radon (above 4.0 pCi/L). High-risk zones: the northern US, Rocky Mountain states, Appalachian region, and upper Midwest. But elevated levels can occur anywhere.

Testing Methods

Short-term test kits: Charcoal canister or alpha track detector. Placed in the lowest lived-in level for 2-7 days. $10-$30 (includes lab analysis). Available at hardware stores or free from many state radon programs. Good for: initial screening. Downsides: results vary with weather and ventilation conditions. A single short-term test is a snapshot, not an average.

Long-term test kits: Alpha track detectors placed for 90+ days. $20-$40 (includes lab analysis). More accurate than short-term tests (averages seasonal variation). Recommended: if initial short-term test is between 2-4 pCi/L, follow up with a long-term test.

1. Continuous radon monitors (CRM): Electronic devices that measure radon continuously. Professional-grade CRMs: used by licensed testers. Consumer devices (Airthings Wave, Ecosense): $100-$
2. 2
3. 0
4. Provide real-time and historical radon data. The best option for ongoing monitoring. Airthings Wave Plus: $230 (also monitors humidity, CO2, VOCs).

How to Test

Place the test in the lowest lived-in level (usually the basement or ground floor). Keep windows and doors closed for 12 hours before and during the test (except normal entry/exit). Do not place near drafts, high humidity, or high heat. Place at least 20 inches off the floor, away from walls. Short-term test: 2-7 days. Send to lab. Results in 1-2 weeks. If the result is 4.0+ pCi/L: do a second short-term test or a long-term test to confirm. If confirmed above 4.0: mitigate.

Mitigation Systems

Sub-slab depressurization (SSD): The most common and effective system. A pipe is inserted through the basement slab into the gravel or soil below. A radon fan (mounted outside or in the attic) draws radon from under the slab and vents it above the roofline. Reduces radon by 80-99%. Cost: $800-$2,500 installed. The gold standard for radon mitigation.

Sub-membrane depressurization (crawl spaces): For homes with crawl spaces instead of basements. A heavy plastic membrane is sealed over the crawl space floor. A pipe and fan draw radon from under the membrane. Cost: $1,000-$3,000.

Heat recovery ventilator (HRV): Increases ventilation to dilute indoor radon. Less effective than SSD (typically reduces radon by 25-50%). Higher operating cost (increases heating/cooling load). Used when SSD is not practical.

Sealing cracks: Sealing foundation cracks, gaps, and penetrations. By itself: NOT sufficient for mitigation (radon finds other pathways). Used as a supplement to SSD systems (improves their efficiency).

Costs

Short-term test kit: $10-$30.

Long-term test kit: $20-$40.

Consumer CRM (Airthings): $100-$200.

Professional radon test: $125-$250.

SSD mitigation system: $800-$2,500.

Crawl space mitigation: $1,000-$3,000.