Radon-Resistant New Construction

Rutherford County is one of the fastest-growing counties in Tennessee, with new subdivisions filling in around Murfreesboro, Smyrna, La Vergne, and Rockvale. If you're building a home, or buying one before the foundation is poured, it's the cheapest moment you'll ever have to deal with radon. The EPA calls the approach radon-resistant new construction (RRNC). Here's what it involves and what to ask your builder.

Why build radon resistance in?

Every new house in a Zone 1 county like Rutherford has a real chance of testing high, and modern energy-efficient homes are tighter than older ones, which can let radon build up. Adding a mitigation system after the house is finished means coring the slab or lining a crawl space that's already full of ductwork and plumbing. Adding the key parts during construction is much simpler, because most of them go in before the slab is poured or the subfloor is built.

The core RRNC techniques

The EPA describes a set of standard features:

1. A gas-permeable layer

A layer of clean gravel, typically about 4 inches, under the slab, or a soil-gas collection mat. This lets soil gas move freely to a single collection point instead of pushing up through the slab.

2. Plastic sheeting

Polyethylene sheeting over the gravel, under the slab, or over the soil in a crawl space. It acts as a soil-gas retarder and helps keep the gravel layer clean when concrete is poured.

3. Sealing and caulking

Sealing of slab openings, cracks, and joints, and of penetrations through the floor, so soil gas can't take shortcuts into the house.

4. A vent pipe

A 3- or 4-inch PVC pipe running from the gravel layer, or from beneath the crawl space sheeting, up through the conditioned space to the roof. With no fan, this is a passive system: natural draft through the pipe can lower radon somewhat.

5. A junction box for a future fan

An electrical outlet in the attic near the vent pipe, so a fan can be added easily if a post-occupancy test shows radon at or above 4 pCi/L. Activating a passive system is usually a quick job.

Passive versus active

A passive RRNC system often reduces radon, but not always enough. An active system adds the fan from the start. Many radon professionals recommend at minimum roughing in for a fan and then testing once you've moved in. If the result is 2 pCi/L or higher, adding the fan is typically simple and effective.

Codes and builders

The International Residential Code includes an optional appendix on radon control methods. It applies only where a local jurisdiction adopts it, and adoption varies. Don't assume your house will get these features automatically. Ask your builder directly, in writing, before the foundation goes in. Some builders offer radon rough-ins as a standard feature or an option; others will do it if asked. Get any agreement into your contract.

Questions to ask your builder

1. Will there be a gravel layer or soil-gas mat under the slab, and plastic sheeting over it?
2. Will you install a vent pipe from beneath the slab or crawl space liner to above the roof?
3. Will there be an electrical outlet in the attic near the pipe for a future fan?
4. Will slab penetrations and joints be sealed?
5. For a crawl space home, will the vapor barrier be sealed at seams and walls with a suction connection?
6. Will the pipe be labeled so future owners and inspectors know what it is?
7. Can I have a radon test done before closing, and will you activate the system if needed?

Testing a new home

Even with RRNC, test once the home is finished and lived in, ideally a short-term test right away and a long-term test through the first winter. New-home buyers in Rutherford County can use the state's free kit or hire a certified measurement professional. If the passive system isn't enough, a certified mitigator can add a fan to the existing pipe.

Already built without RRNC?

Plenty of recently built homes don't have these features. That's fine; a standard mitigation system can be retrofitted to slabs and crawl spaces. It just involves more work than it would have during construction.

Cost context

Builders price RRNC features differently, and we don't have a reliable published average for Middle Tennessee construction, so ask for a line-item price. For comparison, a retrofit active system in an existing home has a typical national range of about $805 to $1,326 according to Angi's 2026 data. That's a national figure, not a local quote.

For builders

If you're a builder or developer in Rutherford County interested in adding radon-resistant features or post-construction testing, we can connect you with certified professionals who work with new construction. Call or use the form and choose "New construction / builder."

What fits new homes in Rutherford County

New subdivisions around Murfreesboro, Smyrna, and Rockvale are built on both slabs and crawl spaces. The EPA's techniques work for either:

• On slabs, the gravel layer and plastic go down before the pour, the vent pipe stub is set in the gravel, and the slab is sealed around penetrations.
• On crawl spaces, the plastic sheeting covers the soil with seams sealed, and the vent pipe connects beneath the sheeting.
• Shallow limestone or dense clay on some lots affects how freely gas moves under the slab, which is one more reason to test after move-in and be ready to add a fan.

More new-construction questions

Is a passive pipe worth it if I'll probably need a fan?

Yes. Even if a fan is needed later, having the pipe already in place makes activation much simpler than a full retrofit.

When should I test my new home?

Test once the home is complete and you're living in it, with the HVAC running normally.

Where this information comes from

• EPA: Radon-Resistant Construction Basics and Techniques
• EPA: Radon Frequently Asked Questions
• EPA Map of Radon Zones, county data (Rutherford County, TN: Zone 1)
• Tennessee Department of Environment and Conservation: Tennessee Radon Program
• Angi: How Much Does a Radon Mitigation System Cost? (2026 national data)