For Builders: Getting Passive Systems Right
Wondering what the new rule means for your next pour? Here’s the short version for new construction radon systems.
Iowa HF 2297 made passive radon systems standard in new single-family homes and duplexes as of July 1, 2026. The rule is simple. The details under the slab are where systems work or fail.
According to Iowa HHS, the state code points to the passive methods in Appendix AF of the 2021 International Residential Code. Before the change, 11 jurisdictions already required them, including Polk County and Altoona. Crews in those areas know the routine.
A June 30, 2026 construction law update added one caution. The Iowa Department of Inspections, Appeals, and Licensing (DIAL) issued enforcement guidance on June 25, and the code amendment itself was still being finalized. Check with your local building department before you lock in plans.
| Component | What it does | Common mistake we avoid |
|---|---|---|
| Gas-permeable aggregate | Lets soil gas move freely to the collection point | Fines or sand mixed into the gravel layer |
| Sub-slab T-fitting or perforated loop | Collects soil gas under the slab | Fitting crushed or buried in fines during the pour |
| Polyethylene soil-gas retarder | Blocks gas from rising through the slab | Unlapped seams and torn sheeting around plumbing |
| Sealed penetrations and joints | Closes the easy entry paths | Open gaps at plumbing stubs and sump basins |
| Passive vent stack | Carries soil gas up and out through the roof | Pipe routed through unconditioned space or with long horizontal runs |
| Attic junction box | Makes future fan activation fast and safe | No power left near the pipe in the attic |
Radon-resistant guidance from the Connecticut Department of Public Health lists the same basics:
- At least 4 inches of clean gravel with no fines
- 6 mil polyethylene sheeting between the gravel and the slab
- A vent pipe of at least 3-inch PVC running from the sub-slab gravel to the roof
- Room and a power source in the attic for a future fan
Here’s a pro tip on the sheeting. A Connecticut radon fact sheet from SOS Radon calls for 12-inch overlaps at seams, sealed with tape. That one step fixes the unlapped seams we see most often.
We work with builders across Polk and Dallas counties, from Waukee and Grimes to Ankeny and Altoona. Tell us your pour schedule and we’ll fit the work in around it.
For Homeowners: Should You Activate Your Passive Pipe?
If your home was built with a passive pipe, start with a test. A 48-hour continuous radon monitor test in the lowest lived-in level tells you where you stand.
The EPA recommends fixing a home at 4.0 pCi/L or higher and considering action between 2.0 and 4.0. Here’s how we read the results for a home with a passive pipe:
- Below 2.0 pCi/L: The passive system may be doing its job. Retest every two years.
- 2.0 to 3.9 pCi/L: Consider activating, especially if you plan to finish the basement.
- 4.0 pCi/L and above: Activation is recommended. It’s usually the fastest, simplest fix since the pipe is already there.
Many owners in growing suburbs like Waukee, Ankeny and the Easter Lake area assume a new home is radon proof. Testing is how you know. Polk County’s health department reports that more than 70% of Iowa homes test above the EPA action level of 4.0 pCi/L.
Our guide on how often to test for radon covers when to retest after you move in.
Why passive isn’t always enough
A passive stack depends on warm air rising in the pipe. On mild days, or when soil under the slab is tight, that draft is weak. An attic fan creates steady suction no matter the weather.
The gap can be big. One radon industry guide from Erase Radon puts passive systems at a 30% to 50% reduction, compared with 95% or more once a fan is running. If your test lands near or above 4.0, that difference matters.
What Activation Involves
Activation turns a passive pipe into an active soil depressurization system. We:
- Confirm the pipe is continuous from the slab to the roof and check for leaks.
- Install a radon fan in the attic on the existing pipe.
- Connect it to the attic junction box or add a dedicated circuit if one wasn’t left.
- Add a U-tube manometer in a visible spot so you can check suction any time.
- Run a post-mitigation test after the fan has run at least 24 hours.
Most activations are finished in a short visit. Because the pipe is already in place, a 2026 cost guide from InspectandTest says homes like yours often need only the fan and electrical work, typically $400 to $800.
Fans do wear out. Angi says most last five to 10 years, so jot down the install date and glance at the manometer now and then.
If testing shows a second slab section, like a slab-on-grade addition, needs its own suction point, we’ll explain why and quote it before doing the work.
Builder or Homeowner, Start Here
The EPA and CDC estimate radon causes more than 21,000 lung cancer deaths in the US each year. Whether you’re planning new construction radon systems or living with a passive pipe today, a little action now pays off.
Builders can request a quote with plans and the pour schedule. Homeowners can book a radon test or send us an existing result. If the result is high, see how our residential radon mitigation team handles homes that need more than a single fan. New to radon? Our overview of radon mitigation in Des Moines covers testing, systems and the warranty in one place.
