Crawl Space and Sump Pit Radon in Older Lincoln Homes
September 1, 2026
In an older Lincoln house the radon question is usually not the slab. It is the dirt-floor crawl space under the addition and the open sump pit in the corner of the basement, and each needs its own treatment.
Lincoln's mixed foundations
Much of Lincoln's housing east of 27th Street and around the university and the Near South was built before the 1960s and has been added onto since. The typical result is a full basement under the original house, a crawl space under a later addition, and a sump pit installed when the basement started taking water. Each is a different radon pathway.
A mitigation system designed for a basement slab alone can leave the crawl space and the pit untouched, and the post-mitigation number does not move the way it should. Crawl space and sump mitigation exists because those two features change the design.
The crawl space: seal the soil, then depressurize
Exposed soil in a crawl space is an open door. Radon does not need a crack when the floor is dirt. The fix is a sub-membrane depressurization system: a heavy polyethylene membrane sealed to the foundation walls and piers, with the suction pipe run under it so the fan pulls soil gas from beneath the sheet rather than from the crawl space air.
The membrane does double duty by cutting moisture, which is why crawl-space radon work often improves musty odors and humidity at the same time. It is also why a torn or poorly sealed membrane quietly defeats the system.
- Membrane: sealed at walls, piers and every seam; the seal is the system.
- Suction: one or more pipes under the membrane, tied into the main vent stack.
- Access: the membrane has to survive service visits to the furnace or plumbing above it.
- Combination: crawl space and basement usually share one fan through a manifold.
The sump pit: cover it, then use it
An open sump pit is a direct connection between the soil under the house and the basement air, and it is often the single largest entry point in a home that has one. The mitigation approach turns the liability into an asset: seal the pit with an airtight, gasketed lid, then use the pit itself as the suction point for the system.
The lid has to leave the pump serviceable and the discharge line intact, and it has to hold under the fan's suction. A pit that was sealed with a loose plywood cover is not sealed.
When the basement slab still needs its own suction
If the slab is large, if the sub-slab material is tight clay, or if the pit sits at one end of a long basement, one suction point may not extend the low-pressure field under the whole floor. A licensed installer tests that with a diagnostic: drill a small test hole, run a vacuum at the proposed suction point, and measure whether pressure drops at the far end.
That diagnostic is the difference between a system that reads 1.5 after install and one that reads 3.9. It is part of a proper mitigation installation on an older, patched-together foundation.
What to expect from the number
Sub-membrane and sump-based systems routinely bring older homes from the high single digits or higher to under 2 pCi/L. The post-mitigation test, run after the fan has been on at least a day and within a month, is the proof. The manometer on the pipe is the ongoing check that the fan is still pulling.
For owners of older houses considering radon mitigation for a Lincoln home with a crawl space or sump, the first question to ask any installer is how they will treat each foundation type, because a one-size answer usually means one of them was skipped.
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Quick Answers
Does covering the sump pit interfere with the pump?
No. Radon-rated sump lids are gasketed and include sealed pass-throughs for the discharge pipe, power cord and any float switch, plus a clear window or removable section for inspection. The pump runs normally.
Can a crawl space just be vented instead?
Venting a crawl space to outdoors dilutes radon somewhat but does not control it, and in Nebraska winters it freezes pipes and raises heating bills. Sub-membrane depressurization is the method licensed mitigators use because it removes the gas at the source.
How do you know the crawl space is the problem?
A short-term test in the lowest lived-in level gives the house number. If the house has a crawl space, the installer inspects it directly and may test under the membrane after install to confirm suction. The system design is based on the foundation, not on guessing which part leaks.