Radon exposure is an invisible but significant health concern across Washington, with an estimated 372 radon-related lung cancer deaths per year statewide. Radon is the second-leading cause of lung cancer in the US and the leading cause among non-smokers. The map below shows EPA radon zone designations for every Washington county, helping you identify higher and lower risk areas.
Radon in Washington by the Numbers
- 372 estimated radon-related lung cancer deaths per year in Washington (EPA / AARST)
- 39,537 homes in Washington have been radon-tested according to AARST state data
- $75M estimated annual medical cost burden from radon-induced lung cancer
- $78M estimated total annual economic burden (medical + productivity)
- The EPA action level is 4 pCi/L — any home in any zone can test above this threshold
EPA Radon Zone Distribution: Washington Counties
The EPA divides US counties into three radon potential zones based on geology, atmospheric conditions, and indoor radon measurements. Zone 1 counties have the highest predicted indoor radon potential; Zone 3 has the lowest. These designations are regional predictions, not measurements of individual homes.
| EPA Zone | Risk Level | Predicted Indoor Average | Washington Counties |
|---|---|---|---|
| Zone 1 | High | Greater than 4 pCi/L | 7 |
| Zone 2 | Moderate | 2 to 4 pCi/L | 14 |
| Zone 3 | Low | Less than 2 pCi/L | 18 |
Important: Homes in Zone 2 and Zone 3 counties can still test above 4 pCi/L. EPA zones reflect average geological potential, not individual home measurements. Testing is the only reliable way to know your radon exposure.
Washington Radon Policy and Regulations
Washington has some radon-related policies in place:
- ✗ State radon certification program
- ✗ Radon concentration standards
- ✓ Homebuyer disclosure required
- ✓ New home radon system required
- ✗ School radon testing required
- ✗ New school radon system required
Frequently Asked Questions
What is a safe radon level in Washington?
The EPA recommends taking action if radon levels reach 4 pCi/L or higher. The US national average indoor radon level is about 1.3 pCi/L. Levels between 2 and 4 pCi/L also merit consideration of mitigation. There is no established “safe” level — any radon exposure carries some cancer risk.
How do I test for radon in Washington?
Short-term radon test kits (2 to 7 days) are widely available at hardware stores and online for around $15 to $30. Long-term tests (90 or more days) provide a more accurate picture of your annual average exposure. The EPA maintains a national directory of certified radon professionals.
How much does radon mitigation cost in Washington?
Radon mitigation systems typically cost $800 to $2,500 installed, depending on foundation type and radon levels. Sub-slab depressurization is the most common approach and reduces radon by up to 99% in most homes. Given that Washington sees an estimated 372 radon-related lung cancer deaths per year, the cost is modest relative to the health benefit.
Explore the national US Radon Zones Map to compare Washington to every other state and see county-level EPA zone data across the country.
