Radon and Real Estate Closings: What Buyers and Sellers Need to Know

Radon comes up in a huge number of home sales, often at the least convenient moment: during the inspection period, with a closing date already on the calendar. Understanding how it typically plays out can save both buyers and sellers a lot of stress.

Is radon testing required to sell a home?

In most states, radon testing is not a legal requirement to sell a home, but disclosure rules often require sellers to share what they already know. If a seller has a past radon test result on file, many states require disclosing it to a buyer, even if the number was fine at the time. Separately, most conventional home inspections in radon-prone regions include an optional radon test as part of, or alongside, the standard inspection, because buyers' agents and lenders are used to it coming up.

How the timeline usually works

• Inspection period. The buyer (often through their inspector) places a radon test kit in the home, typically a short-term test since closing timelines don't allow for a 90-day long-term test.
• Results come back. This usually takes 2 to 5 days depending on the lab.
• Negotiation, if needed. If the result comes back at or above 4.0 pCi/L, the buyer typically has a window (defined in the purchase contract) to request mitigation, a credit toward mitigation, or in rare cases to walk away from the deal.
• Mitigation scheduling. If the parties agree the seller will handle mitigation, a licensed contractor needs to be scheduled, and closing is often delayed a few days to a couple of weeks to accommodate installation and a confirming retest.

Who typically pays?

There's no universal rule, it's a negotiated point in the contract like any other repair request. That said, a few common patterns show up:

• In a buyer's market, sellers more often agree to pay for or credit the cost of mitigation to keep the deal moving.
• In a seller's market, buyers sometimes accept the radon result as-is and plan to handle mitigation themselves after closing, especially if the cost is modest relative to the purchase price.
• Some contracts split the difference, with the seller paying up to a capped dollar amount and the buyer covering anything beyond that.

Why closing delays happen

The most common friction point isn't disagreement over who pays, it's the calendar. A licensed mitigation contractor needs time on their schedule, the installation itself typically takes half a day to a full day, and then a confirming test needs to sit for at least 48 hours before it's read. If the original closing date didn't build in that buffer, everyone ends up asking for an extension at the last minute. Buyers and agents who know a radon test is coming can save real time by scheduling the mitigation contractor's estimate visit as soon as the elevated result comes in, rather than waiting for negotiations to fully wrap up first.

What sellers can do proactively

• If you already know your home has tested high in the past, consider mitigating before listing. It removes a negotiation point entirely and can be a selling feature ("radon mitigation system already installed") rather than a red flag.
• If you're not sure, a cheap short-term test before listing gives you time to plan rather than reacting under a closing deadline.
• Keep any documentation of a prior mitigation system, including the contractor's paperwork and the post-installation test result. Buyers and their inspectors will want to see it.

What buyers should know

• An elevated radon result is common and very fixable. It's rarely a reason to walk away from an otherwise good house, and it's one of the more affordable repair items compared to, say, a roof or foundation issue.
• If the seller has already installed a mitigation system, ask for the post-installation test results and confirm the system's fan is still running (the pressure gauge makes this a 30-second check during a walkthrough).
• A home with an existing radon system isn't a red flag by itself. Many buyers actually prefer it, since it means the issue was already identified and addressed rather than left unknown.

After the sale

Whether mitigation happens before or after closing, it's worth retesting every couple of years, and definitely after any major renovation that disturbs the foundation or slab. New owners unfamiliar with an existing system should locate the pressure gauge and get a quick explanation from the seller or their agent about how to do a basic visual check that the fan is still running.

If you need a licensed or certified mitigation contractor to meet a closing deadline, our state directory lists contractors sourced from official state licensing records, so you can verify credentials before scheduling.