Yes, radon travels upstairs. While concentrations are typically highest in basements and ground floors where the gas first enters from the soil, radon readily moves to second floors and beyond through several well-documented mechanisms. In some homes, upper-floor levels can be high enough to exceed the EPA’s action level of 4 pCi/L.
How Radon Moves Between Floors
Radon enters most homes through cracks and gaps in the foundation, then rises through the building driven by basic physics. The most powerful force is called the stack effect: warm air inside your home rises naturally, creating lower pressure near the ground floor and pulling soil gases (including radon) in through the foundation. That same upward airflow carries radon to every level of the house. Research from the National Institute of Standards and Technology found that even in large buildings, the stack effect can push radon as high as the twelfth floor when outdoor wind speeds are low.
The greater the temperature difference between inside and outside, the stronger this effect becomes. In winter, when your home is significantly warmer than the outdoor air, the pressure difference at the basement level increases, pulling in more radon and driving it upward more aggressively. This is one reason radon levels often spike during cold months.
Forced-Air Systems Spread Radon Quickly
If your home has a forced-air heating or cooling system with ductwork running between floors, radon can be distributed throughout the entire house. The EPA specifically notes that forced-air systems move radon gas efficiently from lower levels to upper living spaces. Your HVAC return vents on the lower level pull radon-laden air into the system, and supply vents on upper floors blow it right back out. This can partially equalize radon concentrations across all floors, sometimes bringing upper-floor levels surprisingly close to basement readings.
Structural Pathways That Act as Conduits
Beyond general airflow, specific structural features in your home create direct vertical channels for radon movement. Plumbing chases, the open cavities in walls where pipes run between floors, function like chimneys for soil gas. Gaps around water lines, gas lines, and electrical conduits that penetrate through the foundation give radon a way in, and the vertical chases these utilities run through give it a way up.
Homes built with concrete block foundations are especially vulnerable. The hollow cores inside those blocks connect directly to the soil and allow radon to fill the cavities, then travel upward through any gaps or cracks in interior wall surfaces. Sump pump pits and floor drains that aren’t properly sealed create additional direct pathways from the soil into your living space, feeding radon into the same airflow patterns that carry it upstairs.
Stairwells also play a role. Open staircases between floors allow warm air to rise freely, and radon moves with it. Homes with open floor plans or two-story foyers may see more radon reaching upper levels than homes with doors separating each floor.
Upper-Floor Radon Sources
Soil gas traveling upward isn’t the only source of radon on upper floors. Building materials themselves emit low levels of the gas. According to the CDC, materials made from sandstone, concrete, brick, natural stone, gypsum, and granite contain naturally occurring radioactive elements that decay into radon. Granite countertops, stone accent walls, and concrete structural elements on any floor can contribute small amounts of radon directly to the air in that room.
That said, the CDC notes these contributions are typically minor compared to what enters through the foundation. The primary concern remains soil gas, but building materials can add to the total, particularly in tightly sealed upper-floor rooms with limited ventilation.
How Much Lower Are Upper-Floor Levels?
As a general pattern, radon concentrations drop with each floor above the basement. A common rule of thumb in radon measurement is that levels decrease by roughly 25 to 50 percent per floor, though this varies widely depending on your home’s construction, airflow patterns, and ventilation. A basement reading of 8 pCi/L might correspond to 4 to 6 pCi/L on the first floor and 2 to 4 pCi/L on the second floor. But homes with forced-air systems, open stairwells, or particularly tight construction on upper floors can show much less of a drop.
The EPA recommends taking action at 4 pCi/L, while the World Health Organization sets a preferred reference level of 2.7 pCi/L. Both organizations acknowledge that no level of radon exposure is truly risk-free. If your basement tests high, your upper floors may still exceed these thresholds, which is why testing on the lowest lived-in level is standard practice. If you spend significant time on an upper floor, testing there separately gives you a clearer picture of your actual exposure.
Mitigation Works for the Whole House
The good news is that the most common fix, active subslab depressurization, addresses radon at its source and reduces levels throughout the entire home, not just in the basement. This system uses a pipe and fan installed through or alongside the foundation slab to pull radon from beneath the house and vent it above the roofline before it ever enters your living space. The EPA reports that this method reduces indoor radon by 50 to 99 percent, and it works best when the material beneath your slab allows air to flow freely.
Because the system intercepts radon before it enters the building, it prevents the gas from reaching any floor. Sealing cracks in the foundation, covering sump pits, and sealing gaps around utility penetrations can improve the system’s performance further. If your upper-floor radon levels are elevated due to forced-air distribution, cutting off the supply at the foundation solves the problem everywhere at once.