Radon-Resistant New Construction in Indiana — Builder and Buyer Guide

March 2, 2026

Indiana buyers of new homes frequently assume that modern construction means no radon problem. This assumption is wrong. A new home can have elevated radon regardless of construction quality — what matters is the soil beneath the foundation, not the age or build quality of the home. The good news: new construction is the best opportunity to address radon cheaply, and the industry has a well-established approach called Radon-Resistant New Construction (RRNC).

What Is RRNC?

Radon-Resistant New Construction (RRNC) is a set of building techniques that prevent radon from entering the home and provide a simple upgrade path if needed. The core components:

1. Gas-Permeable Layer A 4-inch layer of clean aggregate (gravel) under the foundation slab. This creates pathways for radon to move laterally rather than being forced up through the slab.

2. Plastic Sheeting (Vapor Barrier) A continuous polyethylene sheet over the gravel layer, under the slab. This blocks soil gases (including radon) from entering through the soil.

3. Sealing and Caulking All openings in the foundation floor and walls — cracks, utility penetrations, sump pits — are sealed with polyurethane caulk or foam.

4. Vent Pipe (Stub-Out) A 3- or 4-inch PVC pipe runs from the gravel layer through the home to the roof or exterior, creating a vertical pathway. In a passive system, natural stack effect draws some radon up and out. In an active system, a fan is added to create consistent negative pressure.

5. Electrical Outlet A junction box or outlet is installed in the attic or near the vent pipe termination point — so adding a fan later requires no electrical work, just plug-in installation.

A passive system (no fan) is standard in new construction. An active system (with fan) is installed when a post-occupancy radon test shows levels at or above 4 pCi/L.

Indiana Code Requirements

Indiana adopted the 2021 International Residential Code (IRC), which includes Appendix F: Radon Control Methods for buildings in EPA Zone 1 areas. Appendix F describes the RRNC components above and applies to all new residential construction in high-radon zones.

However, Appendix F is an appendix — local jurisdictions must explicitly adopt it. Enforcement is inconsistent across Indiana’s 92 counties:

• Larger jurisdictions (Marion, Hamilton, Allen counties and their cities) are more likely to have building inspectors who verify radon-resistant components.
• Rural counties often have limited building inspection capacity and may not verify RRNC compliance.

What this means for buyers: Do not assume your new Indiana home has radon-resistant features. Ask the builder directly:

• Was a gas-permeable layer installed under the slab?
• Is there a continuous vapor barrier?
• Is a vent pipe installed with an electrical stub-out?
• Was a post-construction radon test performed?

Request documentation. A reputable builder in an Indiana Zone 1 county should be able to provide it.

Testing a New Home

Whether or not RRNC was included, test your new Indiana home after occupancy. Radon levels in a new home can differ significantly from levels during construction (before the slab was poured, before the home was sealed).

Test 90 days after occupancy. A short-term test (48–96 hours) gives a faster result; a long-term test (90+ days) gives a more accurate picture of average exposure. Use a licensed Indiana radon tester for results that carry weight if you later negotiate with the builder.

Activating a Passive System

If your new home has a passive RRNC pipe and your post-occupancy test shows elevated radon, activating the system is straightforward:

1. A licensed Indiana radon mitigator installs an in-line fan on the pipe — typically in the attic or garage.
2. The fan creates continuous negative pressure under the slab, pulling radon out before it can enter.
3. A post-mitigation test (24–48 hours) confirms results.

Typical cost: $300–$600, since all the major components are already in place. Compare this to $1,200–$2,000 for a full installation in an existing home without RRNC features.

For Builders and Developers

Indiana builders working in Zone 1 counties — which is most of the state — should consider RRNC standard practice. The reasons are practical:

• A $400 cost addition during construction avoids a $1,500+ remediation request from a buyer who tests post-close
• Documented RRNC is increasingly expected by buyers using agents educated about radon
• Real estate transactions in Indiana’s major markets now routinely include radon test contingencies
• A passive system that tests under 4 pCi/L is a selling point; a home without one that tests high is a negotiating liability

The incremental cost of doing it right during construction is far less than the cost — and friction — of addressing it post-close.

What to Ask Your Builder

If you’re buying a new home in Indiana, ask these specific questions:

1. Does this home include a sub-slab depressurization-ready RRNC system? (Gas-permeable layer, vapor barrier, vent pipe, electrical stub-out)
2. Has a radon test been performed during or after construction?
3. If yes, what was the result and can you provide the report?
4. If no passive system, will you install one before closing?

Get answers in writing. In Indiana’s Zone 1 counties, this is standard due diligence.

Browse licensed Indiana radon mitigators on this site to find a contractor who can test your new home or activate a passive system already in place.