What Renters Moving Into Basement or Garden- Level Apartments Need to Know About Radon
Roughly one in every fifteen homes in the United States tests above the EPA's safety threshold for radon, and units sitting at or below ground level carry the highest odds of landing in that group. Radon in basement or garden-level apartments is a real, testable risk, not a footnote buried in a rental listing, and renters have more say in how it gets handled than most assume. Because radon is colorless, odorless, and tasteless, testing before or right after moving in is the only way to know what's actually in the air.
Radon is often found in at- or below-ground-level apartments.
Why Is Radon in Basement or Garden-Level Apartments More Common?
Basement and garden-level units sit closest to the soil radon comes from, which is why they consistently test higher than upper-floor apartments in the same building. Radon forms from the natural breakdown of uranium underground, then seeps upward through foundation cracks, gaps around pipes, and unsealed concrete joints.
A unit built partly or fully below grade has more surface area in contact with that soil than a third-floor apartment ever will. Below-grade units are also often sealed tightly for energy efficiency, so radon that does seep in has fewer ways to escape. None of this means every basement apartment has a problem: it means the odds are higher, which is why testing matters more here than it does upstairs.
What Should You Ask a Landlord Before Signing a Lease?
Before signing, ask directly whether the unit has been tested for radon and request copies of any results on file. A landlord's answer, or lack of one, says a lot about how the property has been managed.
Responsibility for testing varies by state and lease terms, but landlords of ground-level and basement units are increasingly expected to test before a new tenant moves in and disclose known results. Figuring out who is responsible for radon testing in a rental property, and when it needs to happen, usually comes down to those same two factors, plus how much initiative either side is willing to take.
How Does Radon Fit Into Your Broader Moving Checklist?
Radon testing belongs on the same checklist as everything else you research before committing to a new address, not treated as a separate, optional step. Rent, commute, and neighborhood safety usually get the attention; air quality inside the unit itself often doesn't.
Anyone in the middle of relocating to a new area is already comparing costs, researching neighborhoods, and visiting properties in person, which makes it a natural moment to ask about radon testing alongside questions about utilities and lease terms. A short-term test kit costs about $15 and takes only a few days to produce results, so there's rarely a good reason to skip the question during that same round of research.
Where Inside the Apartment Does Radon Actually Build Up?
Radon concentrates most heavily in the areas closest to the ground and farthest from ventilation, which in a basement or garden-level unit often means most of the living space. Utility closets housing a furnace or water heater tend to run especially high, since gaps around pipe fittings give radon an easy entry point, and poor airflow in those rooms gives it nowhere to go.
Knowing which rooms pose the highest risk also helps determine where to place a test kit for the most representative reading. The top four areas where radon can build up in the home are basements, the living space directly above them, utility rooms, and bathrooms, where cracks around tubs and toilet bases are easy to overlook.
Are Other Units in the Building at Risk Too?
Other units in the same building can absolutely share the risk, since radon doesn't stay confined to whichever apartment it enters first. Shared foundations, connected HVAC systems, and common basements or parking garages let radon migrate between units in ways a single test in one apartment won't catch, especially in older buildings where ventilation between floors was never designed with radon in mind.
This is especially relevant for renters in larger complexes, where radon mitigation in multi-unit residential buildings requires testing at multiple points throughout the structure rather than relying on one reading from a single unit to represent the whole building. A clean test in a neighboring apartment doesn't guarantee the same result in yours.
What Do the Health Risks Actually Look Like?
The health risks scale directly with radon concentration and how long someone breathes it in. According to the EPA's data on the health risks of radon, radon is the leading cause of lung cancer among people who have never smoked and the second leading cause overall, contributing to roughly 21,000 lung cancer deaths in the U.S. each year.
Those numbers reflect long-term exposure, not a single afternoon in a below-grade unit, which is exactly why testing early in a tenancy matters more than testing years into it.
Prolonged radon exposure can cause significant health issues.
Making Radon Part of Your Move-In Routine
Radon in basement or garden-level apartments isn't a reason to avoid renting one as plenty of below-grade units test well within safe limits but it is a reason to ask before you sign rather than after you've unpacked. A landlord who's already tested, a short-term kit picked up on your own, and a habit of asking the same radon questions you'd ask about rent and utilities cover most of what matters. Add radon to the list of questions for your next apartment tour, right alongside the ones about parking and lease length.