Illinois Radon Disclosure Rules for Home Sellers

A house can look immaculate, appraise well, and still have a radon concern that no walkthrough will reveal. That is why Illinois radon disclosure is part of the real estate conversation before a buyer commits. It gives buyers information the seller already has, but it does not answer the larger question of what the radon level is today.

For buyers, sellers, and agents in Southern Illinois, the distinction matters. Radon is common, odorless, and invisible. A clear disclosure process, paired with a properly conducted test when appropriate, helps everyone make decisions based on facts rather than assumptions.

What Illinois Radon Disclosure Requires

Illinois law requires sellers of most residential real property to provide prospective buyers with a radon disclosure before the buyer is bound by a contract. The required disclosure is intended to alert buyers to radon hazards and their opportunity to test the property.

In practical terms, the seller should provide the state-required radon information and disclose what they know about the home’s radon history. That can include known elevated radon levels, prior test results, and whether a radon mitigation system has been installed. If records are available, providing them is the clearest way to document what was found and what was done.

This is a disclosure requirement, not a guarantee that the home is safe from radon. A seller may have no knowledge of a radon issue because the property has never been tested. That does not mean radon is absent. It simply means there is no known result to report.

Some transfers may be exempt from the standard residential disclosure requirements, and transaction circumstances can differ. Sellers and agents with questions about their specific legal obligations should rely on the current state forms and seek legal guidance when needed. An inspector can explain testing and mitigation findings, but cannot provide legal advice.

Disclosure Is Not the Same as Radon Testing

This is the point that often gets lost in a fast-moving transaction. A seller’s statement tells a buyer what the seller knows. A radon test measures the property under current conditions.

Radon levels can vary with weather, ventilation, building use, foundation conditions, and changes to the heating or cooling system. A test performed years ago can still be useful background information, especially if it led to mitigation, but it is not always a reliable substitute for current testing.

Buyers should also recognize that a neighbor’s test result does not establish the radon level in the home they are purchasing. Two houses on the same street can produce different readings because their foundations, soil contact, and airflow patterns are different.

A professional radon test is commonly conducted over at least 48 hours under controlled, closed-house conditions. The goal is to obtain a dependable snapshot of the air in the lowest livable level of the home. The report should identify the testing device, test period, result, and any conditions that could affect interpretation.

The U.S. Environmental Protection Agency recommends taking action when a home’s radon level is 4.0 picocuries per liter of air (pCi/L) or higher. Lower readings are not zero-risk readings, so a buyer can still choose to discuss mitigation or additional testing based on the result, the property, and their comfort level.

What Sellers Should Disclose About Radon

A good disclosure is direct and supported by documentation. Sellers should avoid guessing, minimizing, or relying on verbal recollections when records can provide a clearer answer.

If the home has been tested, disclose the result and the approximate date of the test. If a mitigation system was installed, disclose that fact and provide available paperwork, such as installation records, warranty information, or follow-up test results. If the system has been serviced or altered, that information may also matter to a buyer evaluating its condition.

A working mitigation system is generally a positive feature, not a defect to hide. It shows that a radon concern was identified and addressed. Still, buyers are reasonable to ask whether the system is operating properly and whether a post-mitigation test confirmed a lower radon level.

Sellers who have never tested should say so honestly through the required disclosure process. Trying to treat a lack of information as proof of a low radon level can create confusion and erode trust later in the transaction.

How Buyers Can Use the Disclosure

Start by reading the disclosure alongside the other property documents, not as an isolated form to sign and forget. If it identifies a prior elevated result, ask whether mitigation was completed and whether a follow-up test was performed. If a system is present, look for the visible components, such as a vent pipe and fan, but do not assume appearance alone proves performance.

A buyer may decide to include radon testing as part of the inspection period. This is especially practical when there is no recent test result, the house has a basement or lower-level living space, or the existing documentation is incomplete. In areas around Marion, Carbondale, and the rest of Southern Illinois, local geology can make radon testing a sensible part of due diligence, but every property should be evaluated on its own merits.

The purchase contract determines what happens if testing identifies a higher result. Depending on the terms negotiated, the buyer may request mitigation, seek a credit, renegotiate, accept the condition, or exercise any available inspection contingency. There is no single right response. The age of the home, the test result, the cost of work, and the overall strength of the deal all affect the decision.

Illinois Radon Disclosure Questions Agents Often Hear

Does a seller have to test for radon before listing?

Disclosure and testing are different duties. The disclosure process requires sellers to provide radon hazard information and report known information as required. It does not automatically mean every seller must conduct a new radon test before listing. A pre-listing test can still be a practical choice because it gives the seller time to understand the result, address an issue if needed, and avoid a last-minute surprise during the buyer’s inspection period.

Does an existing mitigation system eliminate the need for testing?

Not necessarily. A mitigation system should reduce radon, but its effectiveness should be confirmed with testing. Fans can fail, piping can be damaged, and changes to the home can affect performance. A current test provides evidence that the system is doing its job.

Is a low test result permanent?

No. A radon result reflects conditions during a specific test period. It is valuable information, but a future result could differ. Retesting is particularly worth considering after major renovations, foundation work, HVAC changes, or alterations to a mitigation system.

Keep the Decision Grounded in Documentation

Radon should be handled with the same practical mindset as any other inspection finding. Get the required disclosure. Review the records. Test when the transaction and available information warrant it. If mitigation is needed, ask for a defined scope of work and a post-mitigation test rather than relying on a promise that the issue has been fixed.

Miller Home Inspection helps clients understand radon testing results in plain language so they can discuss next steps with their agent, seller, and qualified mitigation professional. The goal is not to create alarm over a manageable issue. It is to replace uncertainty with documentation before the keys change hands.