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Do landlords have to test for radon?

DoorKeeping team

4 min read

There is no federal law requiring landlords to test for radon, and most states do not require it either. Some states require disclosure instead: Illinois landlords must give tenants in units below the third story a radon guide and any records showing a radon hazard, without being required to test. The EPA still says all homes should be tested and recommends fixing a home at 4 pCi/L or more, so testing ground-floor and basement units is a sensible owner habit.

Why radon matters

Radon is a radioactive gas that comes from the ground and collects indoors. The EPA estimates it causes about 21,000 lung cancer deaths a year, about 2,900 of them among people who never smoked, and calls it the number one cause of lung cancer among non-smokers. It recommends fixing a home when radon is at 4 pCi/L or more (EPA, Health Risk of Radon).

The EPA's radon home page says plainly that all homes should be tested (EPA, Radon). Its zone map shows which counties have the greatest potential for high levels, but it is not meant to decide whether one building needs a test: no matter where you live, the EPA says, test (EPA, radon zones).

Illinois: disclosure, not testing

Illinois is a useful example of how a state rule can work. According to the Illinois Emergency Management Agency and Office of Homeland Security (IEMA-OHS), for units below the third story the lessor must (IEMA-OHS):

  • Give the IEMA-OHS pamphlet "Radon Guide for Tenants" on application, before a lease is signed, or during the lease if asked.
  • Give copies of any records or reports on radon in the unit that show a radon hazard.
  • Give the "Disclosure of Information on Radon Hazards to Tenants" form.

The landlord is not required to test. The tenant may test within 90 days of the lease start and must give the landlord the results within 10 days of getting them. If the results show a hazard, the landlord may hire a radon contractor to test within 30 days of being told, and use those results to dispute it. Results are good for 2 years unless the building is renovated or modified. If a tenant's test is above the state's recommended action level and the landlord chooses not to mitigate, the tenant may end the lease.

Other states have their own rules, and some have none. Check with your state radon program and your attorney.

Which units to test

Because radon comes from the soil, the units most worth testing are the ones in contact with or closest to the ground: basement and garden units and the first floor. The Illinois rule's focus on units below the third story follows the same logic. Upper-floor units in a tall building are much less likely to have high levels, though shared shafts and stairwells can carry air between floors.

Example a made-up 36 unit building has 6 garden units, 6 first-floor units and 24 above. The owner buys 12 short-term test kits at $20 each, $240 in total, and tests the 12 lowest units in the same week in winter with windows shut. Two garden units read above 4 pCi/L. A mitigation contractor quotes $2,800 for a sub-slab system serving that end of the building. The owner retests both units after installation.

Running a test program

  1. Pick the units: every basement, garden and first-floor unit, plus any finished lower-level common room.
  2. Give the entry notice your state requires; tenants need to know not to move or open the device.
  3. Follow the kit or professional's instructions on closed-house conditions and test length.
  4. Record each unit, the dates and the result.
  5. For any unit at 4 pCi/L or more, get a mitigation quote from a qualified professional. The EPA lists how to find test kits and professionals on its radon pages.
  6. Retest after mitigation and on a regular schedule, and keep the reports, since Illinois-style laws ask you to share records that show a hazard.

If you test, you may have to share it

Some owners avoid testing for fear of what they will have to disclose. That is a bad trade. In Illinois a tenant can test on their own within 90 days and end the lease if the result is high and you choose not to fix it, so not knowing does not protect you. Knowing lets you fix the problem on your own schedule, budget for it as a capital item and tell tenants the building has been tested.

Radon records in DoorKeeping

DoorKeeping records the cost of test kits and any mitigation system in that property's own books, so a mitigation system shows up as an improvement rather than a repair. Keep each test report in the property's documents, so the results are on file by building. DoorKeeping gives no legal advice; your state's radon program and your attorney decide what you must disclose.

Sources

  1. EPA, Health Risk of Radon, read Oct 29, 2026
  2. EPA, Radon, read Oct 29, 2026
  3. EPA, Map of Radon Zones and Supplemental Information, read Oct 29, 2026
  4. Illinois Emergency Management Agency and Office of Homeland Security, Radon: Lessors and Tenants, read Oct 29, 2026

Questions

Is radon testing required for rentals?
Not by federal law, and not in most states. Some states require disclosure. Illinois requires landlords of units below the third story to give tenants a radon guide and any records showing a hazard.
What radon level is too high?
The EPA recommends fixing a home when radon is 4 pCi/L or more.
Do upper-floor apartments need radon testing?
They are much less likely to have high levels because radon comes from the ground. Start with basement, garden and first-floor units.

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