Is Radon a Problem in Indianapolis, and Should Buyers Test?
Quick answer: Radon is a real consideration for Indianapolis buyers because every Indiana county is rated EPA radon Zone 1 or Zone 2. Mark Dietel Realty suggests most buyers in Marion and Johnson County, Indiana, order a radon test during the inspection period, using a tester certified by the Indiana Department of Health, and plan for mitigation if results reach 4 pCi/L.
What we analyzed: U.S. EPA radon guidance and its Indiana zone map, the American Lung Association's Radon in Indiana page, the Indiana Department of Health radon certification rule (410 IAC 5.1) and Indiana's home inspector statute (IC 25-20.2-2-7), as published in October 2026.
Key takeaways
- Radon is a colorless, odorless gas from soil. The only way to know a house's level is to test it.
- EPA recommends fixing a home at 4 pCi/L or higher, and considering a fix between 2 and 4 pCi/L.
- Indiana requires radon testers and mitigators to be certified by the Indiana Department of Health (410 IAC 5.1).
- A standard Indiana home inspection does not include radon. You add it.
- A high result is fixable, and it is usually handled as a negotiation item.
Is radon actually a problem in Indianapolis?
Radon can be a problem in any Indianapolis house, regardless of age, basement or price. The American Lung Association reports that every Indiana county falls in EPA radon Zone 1 or Zone 2, meaning moderate to high potential. EPA defines Zone 1 counties as having a predicted average indoor screening level above 4 pCi/L.
What most buyers miss: Indiana's home inspector law keeps radon out of the standard inspection report, so in Marion and Johnson County a radon result only exists if the buyer orders the test inside the inspection window. Below we show how that test works and the four ways a high result usually gets settled.
A county zone tells you the odds for an area. Southside Indianapolis has many slab ranches and older basements, and Johnson County subdivisions add crawl spaces and poured basements. Radon can enter through any of them, and two homes on one street can test very differently. That is why EPA and the Indiana Department of Health both point to testing the specific house.
EPA treats radon as a long-term exposure risk, which is why it is worth knowing the level before you own the house. Questions about a test on a house you are buying? Call Mark Dietel Realty at (317) 426-9911.
Should buyers test for radon during the inspection period?
In most Central Indiana purchases, yes. The inspection period in your purchase agreement is the window where a radon result can change the deal, because you can still ask the seller to mitigate or credit the cost. Testing after closing still protects your health, but you will be paying for any fix yourself.
Radon is not part of the standard Indiana home inspection. Indiana Code 25-20.2-2-7 requires the inspector's report to state that it does not address environmental hazards, and radon is named among them. So the test has to be ordered as an add-on.
Ask about it when you book the inspector; some inspectors are also certified radon testers.
How does a radon test work in a real estate sale?
A certified tester places a continuous radon monitor or passive test kit in the lowest livable level of the house, usually for at least 48 hours under closed-house conditions. Windows and outside doors stay shut except for normal coming and going. The tester then reports an average reading in picocuries per liter, written as pCi/L.
Indiana's radon rule, 410 IAC 5.1, requires anyone doing radon testing or mitigation for others to be certified by the Indiana Department of Health. Check that your tester appears on that list.
What happens if the radon level comes back high?
If the result is 4 pCi/L or higher, the usual path is to get a written estimate from an Indiana-certified radon mitigator and include it in your written inspection response. Most buyers ask the seller either to install a mitigation system before closing with a post-mitigation retest, or to give a credit.
Options for handling a high radon result
- Seller installs mitigation before closing
- How it works: Seller hires a certified mitigator; system installed and retested before closing.
- Trade-offs for the buyer: Fixed before you move in; you have less say in contractor and fan placement. Ask for the retest result in writing.
- Seller credit or price change
- How it works: The amount is negotiated in your inspection response; you hire the mitigator after closing.
- Trade-offs for the buyer: You choose the contractor; the work happens after you own the house. Lender approval of credits varies.
- Buyer accepts and mitigates later
- How it works: No change to the contract; buyer budgets for the system.
- Trade-offs for the buyer: Keeps a competitive offer intact; the cost is yours.
- Cancel under the inspection contingency
- How it works: Only if your purchase agreement allows it and you act inside the deadline.
- Trade-offs for the buyer: Rarely necessary for radon alone, because it is a fixable condition.
What does this look like in Central Indiana?
For example, here is a hypothetical. A buyer is under contract at $310,000 on a 2004 two-story with a finished basement in Greenwood (46143). The radon monitor averages above 4 pCi/L. The buyer gets a written estimate from a certified mitigator and asks the seller to install a system before closing, with a retest showing the level below 4 pCi/L.
The seller agrees, because neither side wants to restart the sale over a fixable item. The system goes in before closing, the retest comes back below 4 pCi/L, and the closing date holds.
When this doesn't apply (or who this isn't for)
- Homes with an existing mitigation system: Ask for the original paperwork and run a fresh test. Check that the fan is running and the manometer shows suction.
- Buyers who waived inspections: You can still test after closing for your own health. You lose the ability to negotiate the cost.
- Buyers competing with several offers: Some buyers shorten or skip add-on tests to keep an offer simple. That can help win the house, and the trade-off is that any mitigation becomes your cost after closing.
Test now, or after closing? Testing inside the inspection window keeps your right to ask the seller for mitigation or a credit. Testing after closing keeps your offer simpler, and you pay for any fix yourself. For most buyers in Marion and Johnson County, the window is the better time.
This is general information, not medical or legal advice. For health questions, the Indiana Radon HelpLine is 1-800-272-9723.
What to do next
When you book your home inspector, ask whether they are an Indiana-certified radon tester. If not, line one up before you write an offer. If your test comes back high and you want help reading the result or planning a response, call Mark Dietel Realty at (317) 426-9911. We have offices in Southside Indianapolis, Greenwood and Bloomington.
Frequently asked questions
Do Indiana sellers have to disclose radon?
The Indiana Seller's Residential Real Estate Sales Disclosure, State Form 46234, asks owners to report known conditions, and a seller who knows of a radon test result should answer accurately. Indiana does not require a seller to test. If the seller has a past result or a system, ask for the paperwork.
Is a short-term radon test reliable enough for a home purchase?
A short-term test of at least 48 hours under closed-house conditions is the standard approach in real estate because the timeline is tight. Radon levels vary by season and weather, so EPA notes that long-term testing gives a better year-round average. Many owners retest after moving in.
Can I do my own radon test kit when buying?
You can buy a kit, but in a sale the seller and lender usually expect a result from a tester certified by the Indiana Department of Health. A certified tester's report carries more weight in your inspection response. Do-it-yourself kits are useful for owners testing their own home later.
Does radon matter if the house has no basement?
Yes. Radon enters through the ground contact of any foundation, including slabs and crawl spaces. Slab ranches on the Southside and crawl-space homes in Johnson County can test high. The foundation type changes how a mitigator designs the system. Testing makes sense for every foundation type.
This is general information, not legal or tax advice. Confirm your situation with a real estate attorney, your lender or a certified radon professional.
Mark Dietel Realty — offices in Indianapolis (Southside), Greenwood and Bloomington, Indiana.
