Your Home Inspection Turned Up High Radon. What Happens Next in the Sale

A home sale is the moment a lot of people meet radon for the first time. The buyer's inspector runs a short-term test, and a few days later a number lands in everyone's inbox: 6.1, or 8.4, or 12. The EPA's action level is 4.0 pCi/L (picocuries per liter), so anything above that gets flagged — and suddenly a deal that was cruising along has a new line item nobody planned for.

If that's where you are right now, take a breath. A high radon result is one of the most routine, most fixable things that turns up in a home inspection. It very rarely kills a sale. It's a negotiation, not a disaster.

Why radon gets tested during a sale at all

Radon is a naturally occurring radioactive gas that seeps up out of the soil and collects inside houses. You can't see it, smell it, or taste it, and the EPA estimates it's the second leading cause of lung cancer in the country — behind smoking — accounting for roughly 21,000 deaths a year. Because the only way to know a house's level is to test, radon has become a standard part of a lot of real-estate inspections, especially in regions known to run high.

During a sale the test is almost always a short-term test — a small monitor or kit left in the lowest livable level of the house for a couple of days, under "closed-house" conditions. It's quick because the closing calendar is quick. It's not as precise as a long-term test, but for a go/no-go decision on whether the house needs a fix, it does the job.

Who pays for the fix?

There's no law that assigns it — it's whatever the two parties negotiate. In practice it usually goes one of three ways: the seller agrees to install a mitigation system before closing, the seller gives the buyer a credit to handle it afterward, or they split it. A radon mitigation system — essentially a sealed pipe and a continuously running fan that pulls the gas out from under the slab and vents it above the roofline — typically runs somewhere in the four-figure range for a standard house, which in the context of a home price is small. That's a big reason it rarely derails a deal: the fix is cheap and it's permanent.

Get the fix done by a certified pro — and re-test

Whoever pays, the installation should be done by a certified radon mitigation contractor, not a weekend handyman running a pipe out a wall. A properly designed system routinely pulls a house from double digits down under 4.0, and a good installer will run a post-mitigation test to prove the number actually dropped. Get that follow-up test result in writing — it's the document that closes the loop for the buyer, the seller, and the next owner after them.

If you're the seller reading this before you list

You can get ahead of the whole thing by testing before you list. If your house is high, fixing it on your own timeline — with your own choice of contractor, without a closing clock ticking — is almost always cheaper and calmer than doing it under deadline pressure during escrow. And a house that's already mitigated, with paperwork to show for it, is one less thing for a nervous buyer to flinch at.

The EPA's Home Buyer's and Seller's Guide to Radon walks through the whole process from both sides of the table and is the single best free thing to read if you're staring at a high number mid-sale.

Bottom line

A radon number over 4.0 on an inspection is a speed bump, not a wall. It's cheap to fix, the fix is permanent, and a re-test proves it worked. Whether you're buying or selling, treat it like what it is — a normal, negotiable repair item — and read the EPA's guide so you know what a fair resolution looks like before anyone starts haggling.