Naperville's Radon Disclosure Doesn't Require a Test. Almost Every Sale Gets One Anyway

Every Naperville seller signs the same one-page form at some point before closing, usually without much discussion. It asks whether elevated radon has ever been found in the house, whether there are test records, and whether the seller has any reason to think otherwise. Most sellers initial the box that says they have no knowledge of a problem and move on to the next stack of paper. It feels like a formality, and legally, it is one. Illinois does not require anyone to test a home for radon before selling it.

What the law does not require and what actually happens in a Naperville transaction are two different things. The geology under this city makes radon common enough that buyers test anyway, almost as a matter of routine, regardless of whether the house was built in 1963 or finished last spring. The house's age tells you nothing about its risk. What decides how the radon conversation goes is not the form. It is whether the seller got ahead of the test or found out about it under contract, with a clock already running.

A disclosure that asks for nothing

The Illinois Radon Awareness Act, 420 ILCS 46, took effect in 2008 and set the rule that governs every Naperville sale today. A seller has to hand the buyer a state-approved pamphlet on radon and a signed disclosure form before the buyer is contractually obligated to purchase the property. That is the entire obligation. The Illinois Emergency Management Agency, which administers the act, is direct about what it does not ask for: nothing in the law requires the seller to test the home or fix anything the seller already knows about.

The disclosure form itself is mostly a set of boxes to initial. A seller can state that elevated radon is known to be present, that prior elevated levels were mitigated, or simply that there are no records either way. Checking the last box is not a workaround. It is the honest answer for most Naperville homeowners who have lived in a house for years without ever running a test, and the law was written with exactly that seller in mind.

Why the test happens anyway

None of that stops the test from happening. Radon comes from uranium decaying in soil and rock, and the ground under Naperville sits on glacial till over dolomite limestone bedrock, a combination that gives the gas a path upward into basements and lower levels. Radon testing companies working across DuPage County routinely report indoor readings that sit at or above the EPA and IEMA action level of 4.0 picocuries per liter, which is the threshold both agencies use to recommend mitigation. That pattern does not track with the age of the home, the foundation type, or the price point. A slab, a crawl space, and a full basement all sit on the same soil.

Because the exposure is regional rather than structural, buyers in this market treat a radon test as a normal part of due diligence, not an unusual request. A short-term test runs 48 hours with the house closed up, and it typically happens during the same inspection window as everything else on the punch list. The seller was never legally required to run that test first. In practice, almost nobody skips it, which means the disclosure form and the actual radon conversation in a Naperville deal are two separate events, and only one of them is optional.

Sixty years of foundations, one shared risk

Naperville's housing stock spans more construction eras than most western suburbs, largely because of how much of it one builder put up. Harold Moser's company, Macom Corporation, developed roughly a third of Naperville's homes before he retired in 1993, platting subdivisions across nearly 4,000 acres that included Cress Creek, Moser Highlands, Aero Estates, Maplebrook, and White Eagle. Cress Creek Country Club Estates, the golf-course community Moser built starting in 1963, was the first development of its kind in Illinois. Cress Creek Commons, a separate section of single-family homes and townhomes nearby, went up later, between the late 1970s and the mid-1980s. Decades after that, newer subdivisions like Ashwood Park started construction in the 2000s and, as Crain's Chicago Business documented, stalled for years after the 2006 housing crash before eventually building out.

That spread matters for one reason: none of it changes the radon math. A 1963 house in Cress Creek and a home finished decades later in Ashwood Park sit on the same regional soil profile. Buyers and sellers sometimes assume newer construction means fewer surprises, and for plenty of issues that is true. Radon is not one of them. The risk comes from what is under the slab, not what year the slab was poured.

What actually happens once the number comes back

The mechanics of a Naperville radon result follow a fairly consistent pattern once a buyer's test is in hand.

1. The seller delivers the IEMA pamphlet and signed disclosure form before the buyer is bound to the contract, satisfying the state requirement.
2. The buyer orders a radon test during the inspection period, usually alongside the general home inspection.
3. If the result comes back at or above 4.0 pCi/L, the buyer brings it back to the table as a negotiation item, the same way a roof or furnace finding would be handled.
4. The parties agree on a response: a credit, a price adjustment, or the seller arranging mitigation before closing. Illinois law leaves that response entirely up to negotiation.
5. If mitigation is the path, a licensed contractor installs a sub-slab depressurization system, drilling through the basement slab and running a vent pipe with a continuously operating fan to the roofline. Most installations take a single day, typically four to eight hours.
6. A follow-up test 24 to 48 hours later confirms the level dropped below the action threshold. Properly installed systems can cut indoor radon by up to 99 percent.

Cost estimates for mitigation in the Chicago suburbs have run in a fairly stable range for years, generally between $800 and $2,500 depending on the home's size and foundation complexity. That is a manageable number in the context of a Naperville transaction, but it becomes a much easier number to plan around when it is not a surprise sprung during a tight contract window.

Where sellers lose leverage on the clock

The disclosure law's timing requirement, that the pamphlet and form arrive before the buyer is contractually obligated, is a low bar. Most sellers clear it without thinking twice. The harder question is whether a seller finds out their radon number while they still have room to plan, or finds out because a buyer's inspector delivered it mid-contract with an offer deadline attached.

A seller who tests before listing walks into that conversation with information instead of reacting to someone else's number. If the result is clean, that is a point worth mentioning to a buyer who is going to test anyway. If it comes back elevated, there is time to get quotes, schedule the work on a normal timeline, and price the home with the fix already accounted for rather than negotiating it under pressure after an accepted offer. Given how often Naperville homes end up tested regardless of what the disclosure form requires, treating the test as inevitable and timing it on your own terms is the more useful way to think about it.

A few questions that come up

Does a home with an existing radon mitigation system still need to be retested for a sale? Yes. IEMA and licensed testers recommend retesting every two to four years, mitigated or not, since levels can shift with soil conditions and seasonal changes.

Is a newer Naperville home less likely to have elevated radon than an older one? Not based on what drives the exposure. The gas comes from the ground, not the building materials or the year of construction, so homes across every era, from 1960s Cress Creek to recently completed infill, carry the same underlying risk profile.

If my test comes back high, am I required to fix it before I can sell? No. Illinois law requires disclosure, not remediation. What happens next is a negotiation between buyer and seller, the same as any other inspection finding.

Radon is one of those details that rarely makes it into a listing conversation until it already needs an answer. If you are weighing when to list, what a pre-listing inspection should cover, or how a finding like this fits into pricing strategy for your specific Naperville property, Trevor Pauling Real Estate can walk through the timeline with you before it becomes something to react to. Let's Connect.