My new house already has a radon pipe in it. Do I still need to do anything?

What Minnesota actually requires

Since the 2009 Minnesota Residential Code took effect, every new single-family home built in the state has had to include a passive radon-control system. That is a pretty specific package:

• A perforated drainage layer (gravel) under the entire slab.
• A continuous polyethylene sheet ("vapor retarder") between the gravel and the slab.
• A 3- or 4-inch PVC pipe running from inside the gravel layer, up through the slab, up through the conditioned space, and out the roof.
• A label near the pipe identifying it as a radon system.
• The plumbing rough-in for an electrical box near the pipe in case a fan is added later.

That layout is called passive because nothing pulls the air. It depends on the natural temperature difference between the basement and the outside (the "stack effect") to draw soil gas up the pipe and out above the roofline. When the math works, it works. In Minnesota, the math often does not work.

Why most new Rochester homes still test high

A passive layout works best when:

• The soil under the slab is permeable enough that air moves through it easily.
• The pipe run is short enough that natural stack effect can drive useful flow.
• The slab is well-sealed at every penetration.
• The home's overall pressure dynamics do not actively pull more soil gas in than the pipe can vent.

The Olmsted County radon picture is a textbook case for the active-fan upgrade. Roughly 42% of tested Olmsted County homes are at or above the EPA action level. Dodge County is worse, at roughly 60%. Many of those homes are post-2009 builds with a passive pipe already in place. The passive layout brought the number down some. It just did not bring it below 4 pCi/L.

Adding an inline fan to a builder-installed passive pipe is usually the cleanest mitigation path in the region. The infrastructure is there. The work is mostly running power and installing the fan and the gauge.

How to tell what your builder installed

What you have in the basement

Walk to the mechanical room. Look for a vertical 3- or 4-inch PVC pipe with a label that says something like "Radon" or "Radon Vent." Follow it up. If it just keeps going through the ceiling without anything attached, you have a passive system. If there is a fan on the pipe (often in the attic, sometimes outside the house) and a small U-shaped gauge with a colored fluid, you have an active system.

The gauge tells you if it is running

On an active system, the gauge is called a manometer. The two fluid levels should sit at different heights when the fan is running. If both levels are at zero, the fan is either off, dead, or never installed. A manometer at zero on an "active" system is the most common quiet failure we see on older mitigation work.

The pipe label is required

Minnesota code requires a label on the pipe. If the pipe is unlabeled, it may or may not be a radon pipe. We can tell on a walk-through.

Cities where this comes up most

The new-construction calls we get cluster in:

• Pine Island. About 22 properties a year tested across one census tract. Median 3.7 pCi/L. Most homes are post-2010 builds with the passive layout in place.
• Byron. Median 3.4 pCi/L, on the lower side for the area. Still well above the 2 pCi/L MDH guidance line.
• Kasson. Median 4.7 pCi/L. The newer Kasson subdivisions almost always have the passive pipe, and a fan upgrade is the typical path.
• Stewartville. Median 4.2 pCi/L, mostly driven by the south-side subdivisions which are post-code builds.

What the upgrade looks like

When a builder-installed passive pipe gets upgraded to active, the work is usually:

1. A short-term test to confirm where the home actually sits.
2. A diagnostic visit to measure suction across the slab and check the pipe routing.
3. Installing an inline radon fan, almost always in the attic or outside the conditioned space.
4. Adding a manometer gauge in the basement so you can confirm the fan is working at a glance.
5. A post-install short-term test to confirm the number is below 4 pCi/L (and ideally well under).

Because the pipe and the sub-slab gravel are already there, the upgrade is shorter and less invasive than a fresh install on an older home.

What changes the answer

• How the pipe is routed. A pipe that takes a long indirect path or shares a chase with HVAC ductwork can be harder to fan up.
• Whether the gravel layer is continuous. Some early post-2009 builds put the pipe in but skimped on the under-slab gravel. The fan still works; it just pulls harder.
• Slab penetrations. Sump covers, plumbing penetrations, and crack patterns shape how much suction the fan needs.
• House layout. Walkouts and homes with finished basements need their own thinking on where the gauge goes and how the fan is sized.