Radon Testing in Illinois Homes: What Sellers and Buyers Should Know
Illinois law requires sellers to give buyers a radon disclosure form and the state's radon pamphlet before the buyer is obligated under a purchase contract. It does not require you to test, and it does not require you to mitigate. But if you know about elevated radon, you must disclose it. And interfering with a radon measurement is illegal in Illinois.
That last sentence deserves attention. Opening a window during a buyer's radon test is not a negotiating tactic. It is against the law.
This is also the right time of year to be reading about it. Accurate short-term testing requires closed-house conditions, and those are far easier to maintain once heating season starts.
Questions this guide answers:
- Am I required to test before selling?
- What exactly do I have to give the buyer, and when?
- What happens if the test comes back high?
- Who pays for mitigation?
- What are closed-house conditions?
- Can a seller affect the test result?
- Does a mitigation system hurt my sale?
- Should I test before I list?
George Kolar and Chicago Suburb Living have specialized in Chicago suburban 55+ and active adult real estate since 2005, helping more than 350 clients buy and sell homes. George holds the SRES designation, the National Association of REALTORS credential for working with clients aged 50 and above.
George is a licensed REALTOR, not an attorney or a licensed radon professional. Radon disclosure is a legal obligation and testing is a licensed activity in Illinois. This guide explains the landscape so you know what to ask your attorney and your inspector.
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What Illinois Actually Requires
Two statutes govern this: the Illinois Radon Awareness Act and the Illinois Real Property Disclosure Act.
| Requirement | Does Illinois Require It? |
|---|---|
| Provide the IEMA pamphlet "Radon Testing Guidelines for Real Estate Transactions" | Yes, before the buyer is obligated under a contract |
| Provide the Illinois Disclosure of Information on Radon Hazards form | Yes, same timing |
| Disclose known elevated radon concentrations | Yes |
| Provide existing radon records and reports you have | Yes, where applicable |
| Test the home before selling | No |
| Mitigate if levels are elevated | No |
Read that carefully. The obligation is disclosure, not testing and not mitigation.
The Radon Awareness Act took effect January 1, 2008, so any Illinois transaction since then has carried this requirement.
The Timing Matters
The disclosure and pamphlet must reach the buyer before the buyer becomes obligated under any contract.
If they were not provided before an offer was made, the seller generally must complete the disclosure and give the buyer an opportunity to review the information and potentially amend the contract.
Practically, this means the paperwork belongs in your listing package from day one, not scrambled together after an offer arrives.
What the Disclosure Form Asks
The state form uses initialed statements. In substance, the seller indicates whether elevated radon concentrations are known to be present in the dwelling, whether the seller has provided the buyer with current records and reports, or whether the seller has no knowledge of elevated concentrations.
That middle option is why finding your old test results matters. If you tested in 2014 and have the report in a drawer, that report is part of what you may owe the buyer.
The Rule Nobody Mentions
Interference with the successful completion of a radon measurement is illegal in Illinois.
During a buyer's radon test, a seller cannot open windows, run fans that bring in outside air, move the device, or otherwise affect the reading.
This comes up more than it should, usually not out of malice. A seller airs out the house before a showing, or a family member opens a window because the basement feels stuffy. The test is compromised, the buyer's inspector notices, and the transaction takes on a bad odor that has nothing to do with radon.
If a radon test is running in your home, tell everyone with a key. Contractors, cleaners, family, your agent.
Closed-House Conditions, and Why Fall Matters
Short-term radon tests are the norm in real estate because they fit transaction timelines. Any test lasting less than a week requires closed-house conditions.
| Closed-House Condition | Detail |
|---|---|
| Windows | All closed |
| Doors | Closed except for normal entry and exit |
| Fans and machines drawing outside air | Not operating, with limited exceptions |
| When to begin | At least 12 hours before the test starts |
| How long to maintain | The entire duration of the test |
Exceptions generally include fans that are part of a radon reduction system and small exhaust fans running briefly.
Here is the seasonal point. Maintaining closed-house conditions in July, in a house without central air or with someone who likes the windows open, is genuinely difficult. In October it is the default state of the house.
Fall and winter testing is easier to execute correctly, and results during heating season tend to reflect the conditions you actually live in for much of the Illinois year.
Common Test Types
Devices used in real estate testing generally include activated charcoal canisters, charcoal liquid scintillation vials, electret ion chambers, and continuous radon monitors.
Continuous monitors are frequently used in transactions because they record hourly readings, which makes it possible to see whether conditions were disturbed during the test.
That capability is worth knowing about on both sides. A buyer's inspector can often tell when a window was opened.
Radon testing and mitigation are licensed activities in Illinois. Use licensed professionals, and confirm licensing before hiring.
What If the Test Comes Back High?
The EPA action level is 4.0 picocuries per liter. Results at or above that generally prompt mitigation.
The good news is that radon is one of the more solvable problems a home inspection can surface.
| Compared With | Radon Mitigation |
|---|---|
| A failing roof | Far less expensive |
| A foundation issue | Far less expensive and far faster |
| A sewer line replacement | Generally less disruptive |
| Timeline | Typically installed in about a day |
| Result | A permanent system with a verifiable post-mitigation test |
A typical system vents soil gas from beneath the slab to above the roofline using a fan and piping. After installation, a follow-up test confirms the reduction.
That post-mitigation test is the part sellers should care about, because it converts an open question into documented proof.
Who Pays?
Illinois law does not assign responsibility. It is negotiated, like any other inspection item.
| Scenario | Common Outcome |
|---|---|
| Buyer tests during inspection, result elevated | Frequently negotiated, with the seller paying or crediting |
| Seller tested before listing and mitigated | Seller paid, and it is marketed as a feature |
| Competitive market, multiple offers | Buyer may absorb more of the cost |
| Slower market | Seller more likely to pay in full |
| Seller knew and did not disclose | A legal problem, not a negotiation |
The last row is the one to avoid. Failing to disclose known elevated radon can create liability that lasts well beyond closing.
Should You Test Before Listing?
This is the real decision, and it has arguments on both sides.
The Case For Testing Early
- You find out on your own schedule, not during attorney review.
- You can get multiple mitigation quotes instead of accepting the buyer's number under deadline pressure.
- A mitigated home with a clean post-mitigation test removes the issue entirely from negotiation.
- Some buyers see an existing system as reassurance rather than a red flag.
- It avoids a late renegotiation that can cost more than mitigation would have.
The Case Against
- Once you know, you generally have to disclose. You cannot unlearn it.
- You may spend money on mitigation a particular buyer would never have requested.
- A buyer will often test anyway, and their test governs.
How It Usually Shakes Out
The disclosure objection matters less than it sounds. Buyers in Illinois test routinely, and whatever is in your home will surface during their inspection. The difference is whether you learn about it with months of runway or with a contract deadline in six days.
George's general view for sellers of older Chicago suburban homes, particularly those with finished basements, is that testing early is usually the lower-stress path. Ask your attorney how disclosure applies before you order a test.
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Does a Mitigation System Hurt Resale?
Generally no, and often the opposite.
A visible mitigation pipe sometimes worries sellers who think it advertises a problem. In practice, a documented system with a passing post-mitigation test tells a buyer the issue was identified and permanently solved.
The alternative is an untested home where nobody knows, which is not actually more attractive once a buyer thinks about it.
Keep the installation paperwork and the post-mitigation test results. Those documents are worth more at the closing table than the system's appearance costs you at a showing.
Buyers: What to Do
- Test. The state agency recommends that all homebuyers have a radon test performed before purchase or occupancy.
- Use a licensed professional and confirm the license.
- Read the disclosure carefully. Ask whether prior tests exist and request the reports.
- Ask about closed-house conditions and who is responsible for maintaining them.
- Check for an existing system. If one is present, ask for installation records and the post-mitigation test.
- Test even if there is a system. Fans fail. A system with no recent test is an assumption.
- Build it into your inspection timeline. Short-term tests take days, and attorney review windows are short.
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Radon in 55+ Communities and Newer Homes
Two assumptions worth correcting.
New construction is not exempt. Radon enters through the slab, foundation joints and sump openings. A home built in 2015 can test higher than one built in 1975. Many newer homes are built with passive radon-resistant features, which are helpful but are not a substitute for testing.
Attached homes are not exempt. Townhomes, villas and coach homes sit on slabs or above basements like anything else. If you are buying in a 55+ community, test the specific unit.
If you are purchasing in an association, ask whether the association has any role in mitigation on attached buildings, since a system may involve shared structure. That question belongs in your document review alongside the reserve study.
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Where This Fits in Your Selling Timeline
| When | What to Do |
|---|---|
| 6 months before listing | Look for any prior radon test reports among your home records |
| 3 to 4 months before | Decide whether to test early. Ask your attorney about disclosure first |
| 3 months before | If elevated, get multiple mitigation quotes and schedule the work |
| After mitigation | Obtain and keep the post-mitigation test results |
| Before listing | Have the disclosure form and IEMA pamphlet ready in the listing package |
| Under contract | Maintain closed-house conditions during any buyer test. Tell everyone with a key |
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Frequently Asked Questions
Does Illinois require radon testing before selling a home?
No. Illinois requires disclosure, not testing. Sellers must provide the state radon disclosure form and the IEMA pamphlet before the buyer is obligated under a contract, and must disclose known elevated concentrations.
What exactly must a seller provide?
The IEMA pamphlet "Radon Testing Guidelines for Real Estate Transactions" and the Illinois Disclosure of Information on Radon Hazards, before the buyer becomes obligated under any purchase contract.
What if I already tested years ago?
Existing records and reports may need to be provided to the buyer. Find them before you list rather than after an offer arrives.
Am I required to mitigate if levels are high?
Illinois law does not require mitigation. Whether you mitigate is typically negotiated with the buyer.
Can a seller open windows during a radon test?
No. Interference with the successful completion of a radon measurement is illegal in Illinois, and continuous monitors often record when conditions were disturbed.
What are closed-house conditions?
Windows closed, doors closed except for normal entry and exit, and no fans or machines bringing in outside air, beginning at least 12 hours before a short-term test and maintained throughout.
Is fall or winter a better time to test?
Practically, yes. Closed-house conditions are far easier to maintain during heating season, which makes correct testing simpler.
What is the action level?
The EPA action level is 4.0 picocuries per liter. Results at or above that generally prompt mitigation.
How long does mitigation take?
A typical system is often installed in about a day, followed by a confirmation test.
Who pays for mitigation?
It is negotiated. Sellers frequently pay or credit, though market conditions affect the outcome.
Does a radon system hurt my home's value?
Generally not. A documented system with a passing post-mitigation test resolves the issue permanently, which most buyers prefer to an untested home.
Do new homes have radon problems?
They can. Age is not protective. Newer homes may include passive radon-resistant features, but testing is still the only way to know.
Should I test a townhome or condo in a 55+ community?
Yes. Attached homes are not exempt. Ask about the association's role if a system would involve shared structure.
Can George Kolar help with radon in my transaction?
George is a REALTOR, not an attorney or licensed radon professional. He can make sure the disclosure paperwork is in your listing package from the start, refer licensed testers and mitigators, and handle the negotiation if a test comes back elevated.
Why Work With George Kolar and Chicago Suburb Living
Radon is rarely the thing that kills a deal. It is usually the thing that kills a deal's momentum, because it surfaces late, during attorney review, when everyone is already tired.
George Kolar has worked in Chicago suburban real estate since 2005, has helped more than 350 clients buy and sell homes, and holds the SRES designation for working with clients aged 50 and above. His practice covers DuPage, Kane, Kendall, Will and McHenry counties.
On radon specifically, George can help with:
- Having the required disclosure and pamphlet in the listing package from day one
- Finding prior test reports in your home records before they are needed
- Deciding whether pre-listing testing makes sense for your home and timeline
- Referrals to licensed testers and mitigators
- Getting multiple mitigation quotes rather than accepting one under deadline
- Making sure closed-house conditions are maintained during a buyer's test
- Negotiating the credit or repair if a result comes back elevated
- Presenting an existing system as the resolved issue it actually is
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Final Thoughts
Illinois asks sellers for honesty, not perfection. You do not have to test. You do not have to mitigate. You do have to tell the truth about what you know, and hand over two documents before a buyer signs.
For most sellers the practical advice is simple. Find any old test reports now. Put the disclosure paperwork in the listing package before the first showing. If you test and the number is high, fix it, because it is one of the cheaper and faster problems a house can have.
And if a test is running in your home, leave the windows shut.
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George Kolar, SRES
Chicago Suburb Living | Brokered by eXp Realty
630-479-1400
George@ChicagoSuburbLiving.com
This article is provided for general real estate education and is not legal, health or environmental advice. George Kolar is a licensed real estate broker and is not an attorney, physician, or licensed radon measurement or mitigation professional. Statutory disclosure requirements, approved forms, testing protocols, licensing rules and action level guidance are set by law and by state and federal agencies, and they change. Confirm current requirements with the Illinois Emergency Management Agency and a licensed Illinois real estate attorney, and use licensed professionals for any radon testing or mitigation.
