Updated · Rapid City, South Dakota

New does not mean low. Test after occupancy under normal living conditions. If a passive stack exists, activating it with a fan is often straightforward when results are high.

RRNC and passive systems

Radon-resistant new construction typically includes a layer of gas-permeable material under the slab, plastic sheeting, sealed sumps, and a vertical PVC stack. Without a fan, that stack is passive. Passive systems help some homes and fail to fully control others—measurement decides.

Why Energy-Efficient Building Envelopes Trap Soil Gas

Modern residential construction in Pennington County emphasizes thermal performance—incorporating advanced spray foam insulation, continuous exterior air barriers, and multi-pane low-E windows. While these innovations drastically reduce heating and cooling utility costs during harsh South Dakota winters, they also dramatically decrease natural air exchange rates (measured in Air Changes per Hour, or ACH).

In older, leakier homes, infiltrating outdoor air continually dilutes soil gas entering the basement. In an airtight new construction home, any radon entering through foundation cold joints or unsealed plumbing penetrations becomes trapped, concentrating rapidly to hazardous levels. For this reason, new builds with passive vent stacks frequently test above the 4.0 pCi/L action level until an active inline fan is installed.

When to test a new home

After you move in and the house operates normally through a representative weather period. Real estate short-term tests still apply if you are purchasing a speculative build.

Activating a rough-in

Many activations add an inline fan and verify performance with a manometer plus air testing. See how mitigation works.

Sources

  1. U.S. EPA. Building Radon Out: A Step-by-Step Guide on How to Build Radon-Resistant Homes (EPA 402-K-01-002). epa.gov/radon/building-radon-out
  2. ANSI/AARST. Reducing Radon in New Construction of One & Two Family Dwellings (CC-1000-2023). standards.aarst.org
  3. International Code Council (ICC). International Residential Code (IRC) Appendix F: Passive Radon Gas Systems. codes.iccsafe.org
  4. South Dakota Department of Health. Radon in New Home Construction Guidelines. doh.sd.gov/programs/radon

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Need a local next step? Call (605) 600-6282 to talk through testing, real estate timing, or mitigation for your Rapid City–area home.