Radon

Key Takeaways

• Radon is a naturally occurring radioactive gas with no color, odor, or taste, so testing is the only way to find it.
• Radon gas is named in the environmental section of Washington's seller disclosure statement, Form 17, under RCW 64.06.020.
• Delivery of the seller disclosure statement must occur no later than five business days after mutual acceptance unless the parties agree otherwise, and RCW 64.06.030 then gives the buyer three business days from receipt to rescind.
• RCW 18.86.030 requires a broker to disclose existing material facts the broker knows and that are not apparent or readily ascertainable, and does not require the broker to investigate matters the broker has not agreed to investigate.

What It Means

Radon is a radioactive gas that occurs naturally in soil and rock. It has no color, no smell, and no taste, so nobody walks into a house and notices it. The gas moves with soil gas through cracks in a slab, gaps around pipes, sump openings, and crawl space floors, then collects in the lowest occupied levels of a building. Concentration is what matters. Outdoors the gas disperses into open air. Indoors it can build up, and long exposure at high levels is a recognized health risk.

Because the senses are no help here, the only way to know is a measurement. A test device is placed in the lowest lived-in level of the house and read after a set exposure period, and longer tests give a better picture of the yearly average than short ones. In a purchase, testing normally happens inside the inspection period, alongside the Home Inspector's work, because that is the window in which the buyer still holds the leverage of a Contingency. If a reading comes back elevated, mitigation is an engineering problem with established fixes, and it usually turns into a negotiation over who pays for the system.

How It Works in Washington

Washington approaches radon through disclosure rather than a testing mandate. RCW 64.06.020 sets out the seller disclosure statement known in the trade as Form 17, and its environmental section asks whether there are any substances, materials, or products in or on the property that may be environmental concerns, such as asbestos, formaldehyde, radon gas, lead-based paint, fuel or chemical storage tanks, or contaminated soil or water. The statute says delivery of the disclosure statement must occur not later than five business days, unless otherwise agreed, after mutual acceptance of a written contract to purchase. RCW 64.06.030 then gives the buyer three business days from receipt, or as otherwise agreed, to rescind.

The broker's duty is separate and comes from the agency law. RCW 18.86.030 requires a broker to disclose all existing material facts known by the broker and not apparent or readily ascertainable to a party, and the same section says a broker is not required to investigate matters the broker has not agreed to investigate. A prior radon test result sitting in your file is a Material Fact you disclose. Hunting for radon nobody has measured is not part of the job. Those broker duties are administered by the Washington State Department of Licensing. Our walkthrough of the 2026 Form 35 inspection changes shows where the testing window sits in a live transaction.

Example

Luis and Rosa Alvarado go under contract on a 1978 rambler in Spokane Valley at $415,000, with an inspection contingency on NWMLS Form 35. The seller's Form 17 marks "don't know" on the environmental question that lists radon gas, and it is delivered three business days after mutual acceptance, inside the five-day window in RCW 64.06.020. During the inspection period the buyers pay $185 for a radon test placed in the finished basement. The reading comes back elevated, so they ask for a mitigation system. The seller's listing broker, who has a two-year-old test report from a deal that fell through, discloses it under RCW 18.86.030 rather than waiting to be asked. The parties settle on a $2,900 seller credit at closing and the buyers hire the mitigation contractor themselves.

Common Mistakes and Exam Traps

• Radon has no odor. An exam answer that describes a smell is describing a different hazard.
• Form 17 records what the seller knows. It is not a test, not an inspection, and marking "don't know" is not the same as answering no.
• The five business days in RCW 64.06.020 is the seller's deadline to deliver the disclosure statement. The three business days in RCW 64.06.030 is the buyer's window to rescind after receiving it.
• A broker's duty is to disclose known material facts, not to test for radon. RCW 18.86.030 does not require a broker to investigate matters the broker has not agreed to investigate.