Radon Testing for New Construction Homes

By Steve Crews · Last updated June 23, 2026

Why new does not mean radon-free

The number one misconception about new construction is that the home starts with a clean bill of health on radon. It does not. Radon comes from the soil and rock beneath every building site, and a freshly poured foundation sits on the same earth that produced the gas before the house existed. New homes can actually test higher than older ones, at least initially. Modern construction is sealed tighter for energy efficiency, reducing natural air exchange and allowing radon to build up. An older house with drafty window frames is, ironically, diluting its radon faster.

The EPA estimates roughly one in fifteen US homes has radon at or above the 4 pCi/L action level (about 148 Bq/m3), and that figure includes new construction. For context, Health Canada’s guideline is 200 Bq/m3 and the WHO reference level is 100 Bq/m3 where feasible, but all three authorities agree that lower is better and that no level is risk-free.

What Radon Resistant New Construction actually includes

The EPA developed RRNC guidelines in the 1990s to build radon resistance into homes from the start. These techniques are now required by code in some states and recommended in others. A fully built-out RRNC package has five components:

• A gas-permeable gravel layer (typically four inches) beneath the slab, giving radon a channel that is easier to follow than pushing through concrete
• Plastic sheeting over the gravel before the slab is poured, to block soil gas and moisture from migrating directly into the concrete
• Sealed foundation openings: cracks, sump pits, and utility penetrations are caulked or sealed during construction
• A vertical vent pipe, typically three-inch PVC, running from beneath the slab up through the home and exiting above the roofline
• An electrical junction box in the attic near the pipe, positioned so a fan can be installed later without running new wiring

That last detail is the practical one. A passive RRNC system relies on natural air pressure and temperature differences to draw radon up and out. This helps, but it is not always sufficient. The vent pipe is sized and positioned from the start to accept an inline fan, making an upgrade simple if a post-move-in test comes back above 4 pCi/L.

Passive vs active: what the labels mean in practice

A “passive” RRNC home has the pipe, gravel, and sheeting but no fan. Air movement depends on pressure differences that shift by season, temperature, and wind. Studies suggest passive RRNC systems reduce levels on average by about 50 percent compared to homes without those features. That is useful, but not a guarantee of dropping below 4 pCi/L, especially in areas where soil radon is high.

An “active” system adds an inline fan to the same pipe. The fan runs continuously, maintaining steady negative pressure beneath the slab year-round. Active sub-slab depressurization is the most reliable reduction approach available, capable of cutting levels by 90 percent or more in many homes. If your new home has a passive system and tests above the action level, activating it with a fan is usually a quick job: the pipe is already there, the junction box is already wired, and the mitigator installs and connects the fan.

When to test, and what to use

Timing matters for new construction. Testing the day after closing, before the family has moved in and the HVAC is running normally, can produce readings that do not reflect real-life conditions. A good window is two to eight weeks after move-in, once the home is occupied and the heating and cooling system has had time to settle into its normal circulation patterns.

Check your state radon program before buying anything. Many states offer free or subsidized kits that are the same quality as what you find in hardware stores. Free radon test kits are available through many state programs, and that is always worth checking first. If you prefer to buy one directly, short-term charcoal canister kits (48 to 96 hours in place, then mailed to a certified lab) are inexpensive and easy to use. Check price on Amazon

If you want ongoing monitoring rather than a one-time snapshot, a continuous electronic radon detector shows how levels shift with the seasons and gives you more data to work with. Our guide to home radon detectors covers the main options and what to look for.

Place any test on the lowest level you use regularly. For most new construction that is the main floor, unless the home has a finished basement or a walkout lower level.

What to do if your new home tests above 4 pCi/L

A high reading is not a crisis, but it is a prompt to act. If the home was built with RRNC features, the path forward is usually clear. A certified radon mitigator will inspect the passive system, confirm the vent pipe connects to a proper sub-slab gravel layer, install an appropriate fan, and seal any remaining gaps. Because the passive infrastructure is already in place, the job is typically quicker and less expensive than a full retrofit in an older home.

Ask the contractor to verify what the builder actually installed. In some cases a vent pipe appears in the plans but was never connected to a proper gravel bed, or the attic junction box was skipped during construction to save a little money. Do not assume the build-out was complete.

After any work, retest. That step confirms the system actually brought levels below 4 pCi/L. The EPA recommends a post-mitigation test regardless of how confident the installer is.

If your new home has no RRNC features, the mitigator will core through the slab, install a suction point and pipe, and vent it above the roofline: the same retrofit process used in millions of older homes. See our full breakdown of radon mitigation costs for what to expect.

Questions to ask your builder, and where to find help

State requirements for RRNC vary widely. Some states, including Illinois and several in the mid-Atlantic region, have adopted mandatory RRNC codes. Others only encourage the features. Before your home breaks ground, ask the builder directly: which RRNC components are included? Does the vent pipe actually connect to a gravel sub-layer? Is there a junction box in the attic? These are specific, answerable questions, and a builder who cannot answer them may not have followed through.

Your state radon office (reachable through the EPA’s state program directory) can tell you what is required in your area and usually maintains a list of certified testers and mitigators. For national credentials, look for the AARST-NRPP certification; in Canada, C-NRPP fills the same role. The U.S. Surgeon General has issued a public health advisory recommending that every American test their home, and that guidance covers new homes just as directly as older ones.

FAQ

Does a brand-new home need to be tested for radon? Yes. The EPA recommends testing all homes regardless of age or construction type. New construction sits on the same radon-producing soil as any existing home, and tight modern building practices can concentrate the gas more than an older, leakier house would. Test two to eight weeks after move-in, with the home occupied and the HVAC running normally.

What is RRNC, and does it guarantee low radon levels? Radon Resistant New Construction is a set of EPA-recommended building practices: a gas-permeable gravel layer under the slab, plastic sheeting, sealed foundation openings, and a passive vent pipe ready for a fan. These features reduce radon compared to a home built without them, but they do not guarantee levels below the EPA action level of 4 pCi/L. A test after move-in is still necessary.

My new home has an RRNC pipe but tested at 6 pCi/L. What now? Hire an AARST-NRPP certified mitigator to install an inline fan on the existing passive pipe. Because the infrastructure is already in place, this is typically faster and less expensive than a full retrofit in an older home. Retest after the fan is installed to confirm levels dropped below 4 pCi/L.

Can I use a short-term test kit in a new home, or do I need a professional measurement? A short-term charcoal canister kit, left in place 48 to 96 hours and mailed to a certified lab, is a perfectly reasonable first step and what most homeowners start with. Check your state radon program for free or discounted kits before buying. If the result is elevated, or if you want to track levels over time, follow up with a long-term test or a continuous electronic monitor.