Is radon a problem in the Chicago south suburbs?

Yes. The south and southwest suburbs of Chicago — including Will County communities like Frankfort, New Lenox, Mokena, and Homer Glen, as well as southwest Cook County — sit on geological formations that produce elevated radon. Illinois IEMA data shows roughly 40% of Illinois homes test above the EPA action level of 4.0 pCi/L. Testing every home is strongly recommended.

How much does radon mitigation cost in Illinois?

Radon mitigation for a standard Illinois single-family home typically costs $800 to $1,500 installed. The system uses sub-slab depressurization — a fan and PVC pipe that draws radon from beneath the foundation and exhausts it outside. Always use an IEMA-licensed contractor.

What radon level is safe in an Illinois home?

The EPA recommends action at 4.0 pCi/L or above. However, the EPA also states that any radon exposure carries some risk, and recommends considering mitigation even at 2.0–4.0 pCi/L. A properly installed mitigation system in Illinois typically reduces levels to below 2.0 pCi/L.

Should I walk away from a home with high radon in Illinois?

Not necessarily. Elevated radon is extremely common in Illinois and is fixable. A mitigation system installed for $800–$1,500 resolves the issue in the vast majority of cases. The more important questions are whether the seller will address it and whether the system performs as expected post-installation.

Radon in Illinois Homes: What Every Buyer Needs to Know

Radon is the second leading cause of lung cancer in the United States — and Illinois is one of the higher-risk states in the country. The south and southwest suburbs sit in geological zones where elevated radon is common. Yet most home buyers think little about it until their inspector flags it. This guide covers what radon is, why Illinois buyers need to take it seriously, and what to do when a test comes back elevated.

What Is Radon?

Radon is a naturally occurring radioactive gas produced by the decay of uranium in soil and rock. It seeps upward through the ground and can accumulate in homes — particularly in basements and lower floors where ventilation is limited. It is colorless, odorless, and tasteless. You cannot detect it without a test.

Radon is measured in picocuries per liter (pCi/L). The EPA action level is 4.0 pCi/L — at or above this level, the EPA recommends mitigation. The average indoor radon level in the U.S. is 1.3 pCi/L. Many Illinois homes, particularly in the south and southwest suburbs, test well above 4.0.

Illinois Radon Risk: Why It Matters Here

Illinois is classified by the EPA as having significant radon potential. The Illinois Emergency Management Agency (IEMA) — which oversees the state’s radon program — reports that approximately 40% of Illinois homes test above the 4.0 pCi/L action level.

The south and southwest suburbs sit on glacial till deposits that concentrate radon-producing uranium and radium. Will County, southern Cook County, and surrounding areas show consistently elevated readings compared to national averages. Buyers in communities like Frankfort, New Lenox, Mokena, Homer Glen, Orland Park, and Tinley Park should treat radon testing as essential — not optional.

Radon Testing During a Home Purchase

Radon testing is typically performed as part of the home inspection process. There are two primary methods:

Short-term test (48–96 hours): A charcoal canister or electronic monitor placed in the lowest livable level of the home during the inspection window. Most common for real estate transactions due to time constraints. Results in 2–5 business days.
Long-term test (90+ days): More accurate representation of year-round average levels, but impractical for most purchase timelines.

For real estate transactions, the short-term test is standard. Closed-house conditions (windows and doors closed for 12 hours before and during testing) are required for accurate results. If the seller opens windows during the test period, results may be artificially low — your inspector should verify compliance.

What Happens If the Test Comes Back Elevated

If results are at or above 4.0 pCi/L, you have options:

Request mitigation as a condition of closing: The most common approach. Ask the seller to install a radon mitigation system before closing. This is a reasonable, standard request in Illinois.
Negotiate a credit: The seller provides a closing cost credit and you install mitigation after closing. Gives you control over contractor selection and system design.
Walk away: If the seller refuses to address elevated radon and your contract includes an inspection contingency, you can exit and recover your earnest money.

Radon Mitigation in Illinois

Radon mitigation in Illinois homes almost always uses a sub-slab depressurization (SSD) system — a PVC pipe installed through the basement floor slab connected to a continuously running fan that draws radon from beneath the slab and exhausts it outside above the roofline. It is highly effective, relatively unobtrusive, and durable.

Key facts about Illinois radon mitigation:

Cost: Typically $800–$1,500 for a standard single-family home with an accessible basement. Homes with complex foundations or multiple foundation types may cost more.
Effectiveness: A properly installed SSD system reduces radon levels by 80–99% in most cases, typically bringing levels well below 2.0 pCi/L.
Illinois contractor licensing: Illinois requires radon mitigation contractors to be licensed through IEMA. Always verify your contractor’s license before hiring.
Post-mitigation testing: Test again after installation (typically 24–48 hours) to verify the system is working. Reputable contractors include this in their service.
Ongoing maintenance: The fan runs continuously and should be checked annually. Fan replacement may be needed every 5–10 years. Average fan cost: $150–$300.

New Construction and Radon

Illinois does not require radon-resistant new construction techniques as a statewide code requirement, though some municipalities and builders include passive radon systems voluntarily. Even new homes can accumulate elevated radon. Test any home — new or existing — before assuming it’s radon-free.

For new construction, ask whether the builder installed a passive radon rough-in (a capped pipe beneath the slab). If present, activating it with a fan is significantly cheaper than full installation. See our Illinois New Construction Buying Guide for more on what to ask your builder.