Your builder may have done half the job
Many newer Sioux Falls homes have a radon pipe that's ready for a fan but doesn't have one yet.
The capped pipe in your utility room
Walk into the mechanical room of a lot of newer homes around the Sioux Falls metro and you’ll find a vertical PVC pipe that doesn’t seem to do anything. It comes up out of the slab, sometimes wears a label like “RADON,” and disappears toward the roof. In the attic, that same pipe runs to a vent, with a straight section left empty, waiting.
That’s a passive radon rough-in. The builder ran the vent path while the walls were open, when it was cheap and easy, so it wouldn’t have to be retrofitted later. Gravel and a soil-gas collection point under the slab, a sealed pipe through the house, out the roof. Everything a mitigation system needs except the fan.
Rough-ins show up often in subdivisions built over the last couple of decades, but not reliably. It was the builder’s call, so presence varies house to house and year to year. If you’re not sure what you have, does my new home have a radon system? shows exactly where to look and what the pipe should look like.
Activation: finishing the builder’s sentence
A passive pipe works by natural draft. Warm soil air rises up the pipe on its own, and in some houses that’s enough to keep levels down. In many houses here, it isn’t. The house tests high anyway, and the pipe needs a motor.
Activation typically means adding an inline fan to the existing run, usually in the attic section, along with a u-tube gauge downstairs so you can see the system pulling. The pipe path, the roof penetration, and the slab work are already done. What took a crew a day on a retrofit is mostly already in the walls.
That’s why activation is usually the most direct route to a working system when a newer home tests high. The disruptive parts of a full mitigation install, coring the slab and finding a pipe route through finished space, were handled before the drywall went up. What remains is the fan, the wiring, the gauge, and then the part that actually matters: a follow-up test showing the house came in below the action level of 4 picocuries per liter.
What a rough-in doesn’t promise
Two honest caveats, because this page would be easier to write without them.
A rough-in doesn’t mean your levels are low. Homes with passive pipes still test high all the time. Until a test says otherwise, assume nothing.
And activation doesn’t guarantee the rough-in was built right. A pipe that dead-ends into dirt instead of a proper collection point, or a slab seal that leaks, can hobble the system no matter what fan goes on top. The assessment checks what’s actually under the cap, and the retest proves the finished system performs. When a rough-in turns out to be a dud, the answer is a conventional install — what mitigation involves covers that path.
Found the capped pipe? Start with an assessment
Frequently Asked Questions
My home has a rough-in — am I already protected?
Not necessarily. A passive pipe moves some soil gas by natural draft, but plenty of homes with rough-ins still test at or above the action level. The pipe is a head start, not a system. Test the house; the number decides.
What does activation actually involve?
Typically a fan spliced into the existing pipe run — in the attic on most rough-ins — plus a gauge, a wired connection, and a follow-up test to verify the level came down. It's usually the quickest version of mitigation there is.
Do all newer homes around Sioux Falls have one?
No. Whether a house got a rough-in depends on the builder and the year, and two homes on the same street can differ. The new-home guide on this site shows where to look and what the pipe is labeled.
Can the fan go outside instead of the attic?
Sometimes, depending on how the rough-in was routed. Where the fan can safely and quietly live is exactly what the assessment sorts out before anything is cut.