Passive Radon System in a New Lincoln Home: Does It Work?
September 1, 2026
A passive system is the plumbing for a radon fan without the fan. Under Nebraska's 2019 law most new Lincoln homes have one. It lowers radon; it does not promise a reading under 4, and the test after move-in is what decides whether the fan goes on.
What the 2019 law actually requires
In May 2019 Nebraska enacted section 76-3507, which pulled the radon-resistant construction provisions of the International Residential Code into the state building code. Cities and counties that adopt or conform to the state code enforce them, and Lincoln does. The result is that a house permitted in Lincoln since then generally has radon-resistant features built into the foundation.
The law also required the state to publish county radon averages annually, which is where Lancaster County's 3.6 pCi/L figure comes from. The two provisions were passed together for a reason: the data justified the code.
What is under the slab
A passive system has four parts. A gas-permeable layer, usually four inches of clean gravel, under the slab. A sealed polyethylene vapor retarder over the gravel. A vent pipe, typically 3 or 4 inch PVC, that starts in the gravel, runs up through the house and exits above the roof. And an electrical junction box near the pipe in the attic or garage, ready for a fan.
With no fan, the system relies on the stack effect: warm air rising in the pipe draws a little soil gas up and out. That works, modestly. It is not depressurization; it is a gentle chimney.
- Gravel layer: lets soil gas move toward the pipe instead of the slab cracks.
- Vapor retarder: seals the slab from below; every penetration should be taped.
- Vent pipe: continuous from gravel to roof, labeled, no traps or horizontal runs.
- Junction box: the tell that the builder planned for fan activation.
Why a passive system can still read high
New homes are tight. Less air leaks in, so the small pressure difference between the house and the soil pulls harder on every remaining gap, including the ones the vapor retarder missed. Add a finished basement with a bedroom and the lowest floor is also the most occupied one.
A passive stack also depends on temperature difference. In summer, with the attic hotter than the basement, the draw can reverse. That is why post-occupancy readings in new Lincoln homes come back above 4 often enough that activation is a routine service call.
What activation involves
A licensed mitigator cuts the vent pipe in the attic or garage, installs an inline fan rated for the pipe diameter, wires it to the junction box, adds a manometer on the pipe where it can be read, and confirms suction at the slab. Because the pipe route and the gravel already exist, there is no drilling and usually no new penetrations.
The system then runs continuously as an active sub-slab depressurization system. A post-mitigation radon test after at least 24 hours of fan operation, and within 30 days, documents the drop.
What to check before buying new
Ask the builder for the location of the vent pipe and junction box and for any pre-drywall photos of the vapor retarder. Confirm the pipe is labeled as a radon vent at every accessible point. Then test after move-in, in the heating season if possible, with the house closed up and lived in normally.
For families moving into a new build who want to know whether a Lincoln radon system is already working for them, the honest answer is that the passive part is already there, and the test tells you whether it needs the fan.
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Quick Answers
Do all new Lincoln homes have a passive radon system?
Homes permitted under the current state building code generally do, since the 2019 law added the radon-resistant provisions. Homes built earlier, and some built under older local codes, may not. The vent pipe and junction box are the visible evidence.
Can a homeowner install the fan?
In Nebraska, radon mitigation work must be performed by a state-licensed mitigation business, and the fan installation is mitigation work. Licensed activation also brings the retest and the paperwork.
Where does the fan go?
Outside the living space: the attic, the garage, or outdoors on the vent pipe. Fans are not installed in basements or occupied rooms, because the pipe downstream of the fan is under positive pressure and a leak there would push radon into the house.