Washington has meaningful radon risk, with approximately 25-30% of Washington homes estimated to have levels above the EPA action level of 4.0 pCi/L. The state’s geology — including granitic rock in the Cascade Range and Okanogan Highlands, uranium-bearing basalt formations in eastern Washington’s Columbia Basin, and glacial outwash deposits across the Puget Sound region — creates radon potential across significant portions of the state. The Department of Health administers radon program resources for Washington residents.
EPA Radon Zone Designation
Zone 1 in eastern Washington and portions of the Cascade Range, Zone 2 across western Washington.
Highest-Radon Areas in Washington
Eastern Washington counties overlying the Columbia Plateau basalt and Okanogan granite formations — Okanogan, Ferry, Stevens, Pend Oreille, and Spokane counties — are Zone 1. The greater Seattle area (King, Pierce, Snohomish counties) is Zone 2. The Spokane metropolitan area (Spokane County) is Zone 1 with elevated radon potential.
Radon Contractor Requirements in Washington
NRPP or NRSB national certification. Washington has no separate state radon licensing statute. The Department of Health maintains radon program resources. Verify contractor credentials at nrpp.info or nrsb.org before engaging any radon professional for measurement or mitigation work.
Radon Disclosure in Washington
Washington’s seller disclosure law requires disclosure of known material defects through the Washington Seller Disclosure Statement. Known elevated radon conditions are material information. Radon testing is recommended statewide and is common in eastern Washington transactions.
Testing Resources for Washington Residents
Contact the Department of Health for the most current list of certified radon professionals, any available test kit programs, and jurisdiction-specific requirements that may have been updated since this page was last reviewed. The national NRPP contractor directory (nrpp.info) is searchable by zip code and provides real-time certification verification.
Frequently Asked Questions
Is the Seattle area high in radon?
The greater Seattle area (King, Pierce, Snohomish counties) is Zone 2 with moderate radon potential. Testing is still recommended for all Seattle metro homes, particularly those with basements. Eastern Washington (Spokane area) has higher radon concentrations.
Does Washington require radon contractor licensing?
NRPP or NRSB national certification is required. No separate Washington licensing statute. Verify credentials at nrpp.info or nrsb.org before hiring.
What parts of Washington have the highest radon?
Eastern Washington counties — Okanogan, Ferry, Stevens, Pend Oreille, and Spokane — overlying Columbia Plateau basalt and Okanogan granite have the highest potential. The Spokane metropolitan area is Zone 1 with elevated risk.
Spokane and Eastern Washington Radon
Spokane County is Zone 1 — the highest-radon area in Washington State. The Spokane area’s geology includes granitic basement rock, Columbia River Basalt, and glacial outwash that create elevated radon conditions. The city of Spokane and its suburbs (Spokane Valley, Liberty Lake, Cheney, Medical Lake) all have elevated radon potential. Pend Oreille County and Stevens County in the northeastern corner of Washington overlie the Selkirk Mountains granitic geology with very high radon potential. Ferry County (Republic area) and Okanogan County in north-central Washington also show Zone 1 characteristics.
Puget Sound Region Radon
The greater Seattle area — King, Pierce (Tacoma), and Snohomish (Everett) counties — is Zone 2 with moderate but meaningful radon risk. Kitsap County (Bremerton, Bainbridge Island) and Thurston County (Olympia) are Zone 2. The Puget Sound lowlands’ glacially deposited soils have lower radon production than eastern Washington’s bedrock geology, but Zone 2 represents thousands of homes with elevated concentrations. South King County (Auburn, Kent, Renton) and Pierce County’s Puyallup Valley communities show moderate radon levels. Snohomish County communities closer to the Cascade foothills (Monroe, Snohomish, Granite Falls) show higher readings than lowland communities.
Washington Testing Resources
The Washington State Department of Health (DOH) Office of Radiation Protection administers the state radon program. DOH provides certified contractor information, county-level radon survey data, and educational resources. Washington participates in EPA’s SIRG program. Contact DOH for the current certified contractor list. The Washington State Geological Survey provides detailed geological radon potential information for homeowners seeking sub-county context. Search nrpp.info by zip code for certified Washington radon contractors.
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