The timeline is the problem
Inspection periods run days, not weeks. A short term test needs 48 hours minimum plus lab time if it is a charcoal kit. That is why transaction testing is almost always done with a continuous monitor: the result is available immediately when the device is picked up.
Practical consequence: order the radon test at the same time as the home inspection, not after you see the inspection report. Waiting is how buyers run out of contingency period.
Who does the test matters
In a transaction, neither the buyer nor the seller should place the detector. Testing is done by a neutral certified professional, for a reason that is not hypothetical: results get tampered with. Opening a basement window for a day drops a reading substantially, and continuous monitors exist partly to catch exactly that. They log movement, and they log sudden pressure and humidity changes.
Who pays
Usually the buyer pays for the test, because it is their due diligence. If the result comes back above 4.0, mitigation gets negotiated, and in this market it commonly ends as a seller credit or a seller paid installation before closing. A system costs a fraction of a typical price reduction, which is why most sellers take that trade.
If you are selling
Consider testing before you list. Two reasons, and the second is the one that surprises people:
- A known result removes a surprise that can stall a deal at the worst moment.
- An already installed and documented system stops being a defect and becomes a feature. Buyers in a Zone 1 county understand what it means.
Washington does not require radon testing to sell a home, but it does require disclosing what you know. If you have tested and the result was high, that is a known material fact.
If you are buying
- Ask whether the house has ever been tested, and for the result in writing.
- If there is already a system, ask for the post mitigation test and check the manometer during your walkthrough.
- New construction is not exempt. Radon resistant construction reduces risk but does not guarantee a low number, and it still has to be tested.