Radon testing in apartments measures the concentration of a naturally occurring radioactive gas that can seep into living spaces from the ground below. The EPA recommends action when indoor radon levels reach 4 pCi/L (picocuries per liter) or higher, and suggests considering mitigation even at levels between 2 and 4 pCi/L, because there is no known safe level of exposure. For apartment renters, testing raises unique questions about who’s responsible, which units are most at risk, and what your options are if levels come back high.
How Radon Gets Into Apartment Buildings
Radon is a colorless, odorless gas produced by the natural breakdown of uranium in soil and rock. It seeps into buildings through cracks and openings in foundations. Outdoors, it disperses harmlessly into the air. Indoors, it can accumulate to concentrations high enough to significantly increase lung cancer risk over years of exposure. Radon is the second leading cause of lung cancer after smoking.
In apartment buildings, radon enters the same way it does in single-family homes, but the risk isn’t evenly distributed across units. Ground-floor and basement-level apartments are far more likely to have elevated levels because they sit closest to the soil where the gas originates. Upper-floor units generally have lower concentrations, though building design, ventilation systems, and construction materials can all influence how the gas moves through a structure. Two apartments in the same building can have very different radon levels.
What the Test Actually Involves
Radon testing is straightforward. The most common approach for individual renters is a small test kit that you place in the lowest lived-in area of your apartment, typically a main living space rather than a closet or bathroom. You leave it undisturbed for a set period, then mail it to a lab for analysis. Kits cost between $10 and $30 and are available online, at hardware stores, or through regional radon information centers run by state health departments.
There are two main types of passive test kits. Short-term tests measure radon levels over two to four days. They give you a quick snapshot and are useful as an initial screen. Long-term tests run for a minimum of 91 days, typically six to twelve months, and provide a much more accurate picture of your actual average exposure. Since radon levels fluctuate with weather, soil moisture, and ventilation patterns, a long-term test is the better tool for deciding whether mitigation is truly needed.
Consumer digital radon monitors, which cost $100 to $200, offer continuous readings but come with a caveat. Most are not approved by the National Radon Proficiency Program or National Radon Safety Board because they can’t be calibrated and don’t meet quality assurance standards. Some have shown decent accuracy in research, while others have not. These monitors are not considered reliable enough for making mitigation decisions or for use in real estate transactions.
For multi-family buildings, professional testing by a certified radon measurement specialist is often the better route. A professional can test multiple units systematically and produce results that carry more weight with landlords, property managers, or housing authorities.
Which Units Should Be Tested
Not every apartment in a building needs to be tested, but a single test in one unit doesn’t tell you much about the building as a whole. The priority is units at, below, or near ground level, since those have the highest risk of radon accumulation. In a large apartment complex, a representative sample of ground-contact units gives the most useful picture. HUD recommends following the testing standards developed by the American National Standards Institute and the American Association of Radon Scientists and Technologists, which outline protocols specifically for multi-family buildings.
If you live on an upper floor, your risk is lower but not zero. Radon can travel through elevator shafts, utility chases, and shared ventilation systems. If your building has tested high at ground level, it’s worth testing your unit regardless of floor.
Who Is Responsible for Testing
This is where things get complicated. There is no federal law requiring landlords to test for radon or disclose known radon levels to tenants. HUD guidance encourages radon consideration in federally assisted housing projects and requires mitigation plans when levels at or above 4 pCi/L are documented, but the agency’s general policy notice stops short of imposing mandatory testing requirements on all properties.
At the state level, only a handful of states require landlords to disclose radon information to tenants. Colorado, Florida, Illinois, and Maine have disclosure laws on the books. In the vast majority of states, landlords have no legal obligation to test for radon or tell you about past test results. That means in most of the country, radon testing in a rental apartment falls to you as the tenant.
If you want to test, check your lease first. Some leases restrict modifications or testing without landlord approval, though placing a passive test kit in your apartment typically doesn’t require permission since it involves no changes to the unit. If you get results at or above 4 pCi/L, notifying your landlord in writing creates a record. Many landlords will address the issue voluntarily once they’re aware of documented high levels, partly because of liability concerns.
What Happens If Levels Are High
Radon mitigation in apartment buildings usually involves a sub-slab depressurization system: a pipe and fan setup installed beneath the building’s foundation that pulls radon gas from the soil and vents it above the roofline before it can enter living spaces. These systems are effective, often reducing indoor radon levels by 80% or more. In a multi-family building, one well-designed system can protect multiple units.
The challenge for renters is that mitigation requires building modifications that only the property owner can authorize and pay for. If your landlord is unresponsive, your state’s radon program (typically housed within the health department or environmental agency) can sometimes intervene or provide guidance. In states with disclosure laws, a documented high test result may trigger a legal obligation for the landlord to act.
If mitigation isn’t happening and your levels are significantly elevated, improving ventilation in your apartment can help reduce concentrations in the short term. Opening windows, running exhaust fans, and sealing visible cracks in floors or walls won’t solve the problem, but they can lower your exposure while you work toward a permanent fix.
Why Testing Matters Even in Apartments
There’s a common assumption that radon is only a concern for homeowners with basements, but apartments on or near ground level face real risk. Radon exposure is cumulative. The longer you breathe elevated levels, the greater your lung cancer risk. If you spend most of your time in your apartment (sleeping, working from home), your exposure hours add up quickly. A $15 test kit and a few days of patience can tell you whether you’re living with a fixable hazard or breathing easy.