Seattle Metro, WA Radon Information

Radon levels in the Seattle Metro area are driven by the local soil and bedrock composition, which contains naturally occurring uranium. As uranium decays, it produces radon gas that migrates upward through the soil and enters homes through foundation cracks, sump pits, and gaps around pipes. Homes with basements and crawlspaces are especially susceptible because these below-grade spaces are in direct contact with the soil where radon concentrations are highest.

Professional radon mitigation in the Seattle Metro metropolitan area typically costs between $800 and $2,500, depending on the size and construction of your home. The most common approach is an active sub-slab depressurization system, which a certified contractor can usually install in a single day. Ongoing energy costs for the mitigation fan are minimal—roughly $5–$10 per month—and most systems reduce radon levels by 90% or more.

Radon testing and disclosure requirements vary by state and municipality. Some Washington jurisdictions require landlords to disclose known radon levels or test results, while others have no mandate. Regardless of local law, the EPA recommends radon testing for all residential properties—including rentals—since radon is the second leading cause of lung cancer in the United States.

Yes. High radon levels do not prevent a home sale, but buyers in the Seattle Metro market routinely request radon testing during the inspection period. If levels exceed 4.0 pCi/L, the buyer may negotiate for the seller to install a mitigation system before closing. Having a radon mitigation system already in place can actually be a selling point, demonstrating proactive home maintenance and providing documented proof of safe indoor air quality.