My neighbor tested low. Are we just unlucky?
Why two neighbors can read so differently
Slab and foundation differences
Two homes built from the same plans usually do not have identical foundations. One pour happens on a colder day and ends up with more cracking. One slab gets a penetration for a sump pit and the other does not. The cold joint where the slab meets the wall is sealed differently on different jobs. None of that is visible from the curb, but all of it changes how easily soil gas gets in.
House pressure differences
A home with a tighter envelope and a larger furnace can pull harder on the basement than a leaky home next door. A home with a basement bathroom exhaust fan that runs often, an open-combustion water heater, or a kitchen range hood that vents outside all create negative pressure in the lower level. That pressure pulls more soil gas in.
HVAC and sealing differences
Sealed sump covers, intact slab penetrations, and well-maintained drain tile all reduce soil-gas entry. A home where the sump cover cracked five years ago and never got replaced reads higher than the same home next door whose cover is intact.
Within-Rochester variation
The MDH 2014 to 2023 data tracks 28 Rochester census tracts. Median radon by tract ranges from 2.2 to 5.3 pCi/L. The highest tract sits at about 2.4 times the lowest. That is just the citywide picture. Within any one tract, the spread between individual homes is even wider. We have walked basements on the same block where one home tested 1.8 and the next tested 6.2.
See the full Rochester data set for the tract-by-tract picture.
What does correlate, weakly
- Year built. Post-2009 Minnesota homes have a passive radon-control layout in place. Pre-2009 homes do not. The passive layout reduces the average by some amount but rarely brings the home below 4 on its own.
- Foundation type. Full basements tend to read higher than walkouts. Walkouts tend to read higher than slab-on-grade. Homes with crawl spaces vary widely.
- Builder package. Subdivisions where one or two builders did most of the work tend to have similar foundation details. Indoor numbers still vary, but the starting line is closer.
- Neighborhood geology. A neighborhood on shallow limestone (more common in Rochester's south and east tracts) tends to read higher on average than a neighborhood with thicker glacial cover (more common in the central and west).
None of these correlations are strong enough to skip testing your own home. They tell you a baseline. They do not tell you your home's radon level.
The other half of this question
The other version of this call is: "My test came back high. My neighbor's came back low. I think mine must be wrong." Almost always, the test is right. The neighbor's home is different from yours in some way you cannot see from outside.
If you want a sanity check, the right move is a long-term test (90 days or more) in your home. The long-term number averages across seasons and weather and gives a more honest read than a single short-term result. If both the short-term and long-term tests come back high, the picture is real.
What changes the answer
- How the tests were run. A neighbor who tested in July with windows open will read low, even if their house actually runs high. A test on the second floor reads lower than a test in the basement.
- How long ago the neighbor tested. Radon can shift over time as homes get renovated, slabs settle, and HVAC systems change.
- Whether the neighbor has mitigated. A neighbor with a system in place reads low for a different reason than a neighbor who never needed one.
- How the homes differ. Walkout versus full basement, finished versus unfinished basement, slab versus slab-plus-crawl, sealed sump versus open sump. Any one of these can flip the comparison.