If you're buying or selling a home in Oakland County, Michigan, radon is one of the few inspection-related issues that can reach into a home's basement and quietly affect the health of every person who lives there. It's also one of the easiest issues to test for and, if elevated, to fix. This guide walks you through everything an Oakland County buyer or seller actually needs to know — what radon is, what the EPA's zone designation actually means for our area, how testing works, what the results mean, and what mitigation actually costs in Michigan.
Radon is a colorless, odorless, tasteless radioactive gas. It is produced naturally by the radioactive decay of uranium in soil and rock. Because it's a gas, it seeps up through the ground and accumulates in enclosed spaces — basements, crawl spaces, slab-on-grade ground floors. Outdoors it dissipates harmlessly. Indoors it doesn't.
According to the EPA, long-term exposure to elevated indoor radon is the leading cause of lung cancer among non-smokers in the United States, and the second leading cause of lung cancer overall after smoking. Because the gas is invisible and produces no symptoms in the short term, the only way to know if a home has a radon problem is to test for it.
The EPA Map of Radon Zones classifies every U.S. county into one of three tiers based on the predicted average indoor radon concentration in that county:
Here is the actual EPA zone designation for the six counties we serve in Southeast Michigan:
The reason any part of Lower Michigan shows elevated radon at all is geological — the bedrock and glacial soils across the region contain uranium-bearing minerals. As that uranium naturally decays, it produces radon, which migrates upward through soil and enters homes through cracks in the foundation, gaps around pipes and conduits, sump pump openings, and porous concrete.
Radon is measured in picocuries per liter of air (pCi/L). Here's how to think about the numbers:
The EPA estimates that long-term exposure at 4 pCi/L corresponds to a meaningful increase in lifetime lung cancer risk — comparable, by the EPA's own published estimate, to smoking roughly half a pack of cigarettes a day. That's why testing matters even in Zone 2 and Zone 3 counties: you're committing to potentially decades in the home, and the test is inexpensive insurance.
There are two categories of test, both of which we offer as part of a home inspection in Oakland County:
Short-term radon tests typically run 48 to 96 hours and measure the average radon concentration over that period. We use continuous radon monitors (CRMs) that take an hourly reading, calculate the average, and provide a tamper-evident chain-of-custody record so the results are defensible in a real estate negotiation.
During the test, the home must be kept under "closed-house conditions" — windows and exterior doors closed except for normal entry and exit. We place the monitor in the lowest livable level of the home, away from drafts, exterior walls, and HVAC vents. The test follows EPA Protocols for Real Estate Transactions.
Long-term tests run for 90 days to a year and provide a more accurate picture of average year-round exposure, since radon levels swing seasonally (typically higher in winter when homes are sealed up). For real estate purposes the short-term test is standard; long-term tests are more appropriate after move-in to validate or monitor over time.
Don't panic. Radon mitigation is a mature, well-understood, and reasonably affordable retrofit. The standard approach in Michigan is called Active Sub-Slab Depressurization (ASD), and it works by installing a sealed pipe that runs from below the basement slab up through the home and out the roof, with a continuously running fan that pulls radon out from under the foundation before it can enter the home.
An ASD system installed by a licensed Michigan radon mitigation contractor typically reduces indoor radon levels by 50–99%, regularly bringing homes from 10+ pCi/L down to under 1 pCi/L. After installation, a post-mitigation test confirms the system is performing.
As of 2026, a typical residential radon mitigation system in Oakland County costs $1,200 to $2,500 installed, depending on:
In a real estate transaction, mitigation cost is almost always negotiable. If a buyer's inspection reveals elevated radon, the seller will frequently agree to either install mitigation before closing or credit the buyer the cost at closing. We've seen this go both ways — be prepared to negotiate, and don't walk away from an otherwise good house over a $1,500 fix.
Yes. A mitigation system can fail — the fan can die, the pipe can develop leaks, sub-slab conditions can change. Always test even if a system is in place.
For peace-of-mind testing in your own home, yes — DIY charcoal canister kits are inexpensive and reasonably accurate. For real estate transactions, no. EPA Protocols for Real Estate Transactions require a chain-of-custody continuous radon monitor placed and retrieved by a certified professional.
Yes. New homes can and do test high. In fact, well-sealed modern construction sometimes traps radon more efficiently than older, leakier homes. Always test, regardless of the home's age.
No. Radon mitigation is not covered by standard homeowner's insurance — it's considered a maintenance issue. That's part of why catching it during the inspection contingency, when the seller may pay, matters so much.
Test every house. Oakland County's EPA Zone 1 designation means the predicted county-wide average is already above the 4 pCi/L action level, but individual homes still vary widely from that average — some test low, plenty test much higher — and we regularly find Oakland County homes well above the action level. The test is inexpensive (typically $150–$200 added to your home inspection), the results are conclusive, and if a problem exists, it's fixable for a few thousand dollars — almost always negotiable with the seller. Skipping radon testing in a Zone 1 county is the inspection equivalent of skipping a smoke detector because there hasn't been a fire yet. Don't do it.
When you book a home inspection with us, we offer EPA-protocol continuous-monitor radon testing as an add-on. Schedule it together with the inspection so the test runs during the inspection contingency window and you have full negotiating leverage.