Marcus closed on his newly built home in the spring. He felt good that everything was fresh, modern, and up to current code. When a neighbor mentioned radon testing a few months later, Marcus assumed it did not apply. The house was brand new. No cracks in old walls, no crumbling foundation, no decades of wear. Then he learned the radon in his finished basement measured 6.2 pCi/L, well above the EPA action level of 4.0 pCi/L. His builder had roughed in a passive radon pipe, but without an active fan, it was not doing the job.
New construction does not mean low radon. Radon comes from uranium in the soil and rock beneath a home, and that geology exists no matter when the house was built. If the ground under a new home has elevated radon potential, the gas finds its way in through slab joints, pipe penetrations, sump pits, and even porous concrete. Understanding what causes high radon levels in a home makes clear that new construction radon depends on the soil, the foundation design, and indoor air pressure, not the age of the build.
The good news is that new homes often get a head start, because many builders include radon-resistant features during construction. But those features do not guarantee safe levels, and a passive system alone may fall short. Testing after move-in is the only way to know where you stand. If you are a builder who wants to spec these systems correctly from the start, Radon 1 works directly with builders across Tennessee and the surrounding region.
Key Takeaways
New homes still need testing: Radon in a new home depends on soil conditions, not construction age, and any home can test above 4.0 pCi/L.
Passive systems have real limits: A passive pipe relies on natural air movement, which often falls short of reliable reduction.
Converting to active is straightforward: Adding a fan to an existing passive pipe activates sub-slab depressurization and sharply improves performance.
Test after move-in: Test once the home is occupied and running normally, since a sealed, empty house does not reflect daily life.
Zone maps are no substitute for testing: Tennessee includes EPA Zone 1 counties, but high levels occur in all zones. A map cannot tell you what is under your home.
Post-mitigation retesting confirms results: After any install or upgrade, a follow-up test documents the reduction. Radon 1 includes this step on every job.
Call Radon 1 at (615) 257-9818 to schedule testing for your new home or to upgrade an existing passive system to active.
Why New Homes Can Still Have High Radon Levels
Radon enters a home through pressure-driven flow from the soil. A home’s interior usually sits at slightly lower pressure than the ground beneath it, so it draws soil gas inward through any available path. Those paths exist in every home, including brand new ones. Slab-edge seams, gaps around plumbing rough-ins, hollow block walls, and the natural porosity of concrete all let gas migrate in. The home’s age has no effect on the geology below it.
Radon is a naturally occurring radioactive gas produced as uranium in soil and rock breaks down. That process is continuous, and it has nothing to do with when a house was built on top of it. The EPA and the U.S. Surgeon General both recommend testing every home, whatever its age, construction type, or location. That advice exists precisely because assumptions about new construction lead people to skip a test they should run.
One more factor matters. New homes are often sealed tightly for energy efficiency. Tight construction cuts drafts and lowers utility bills, but it also limits the natural air exchange that would otherwise dilute radon. A well-insulated, tightly built new home can actually trap radon more effectively than an older, draftier one.
What Are Passive Radon Systems in New Construction?
A passive system usually includes a PVC pipe that runs from beneath the slab, up through the home, and out the roof. A vapor barrier may also go into crawl space areas to limit soil gas entry. This setup is part of radon-resistant new construction (RRNC), supported by the EPA’s RRNC standards, which encourage builders to install these parts before slabs and finishes make access hard.
The passive design uses natural stack effect and pressure differences to pull some radon out through the pipe, with no fan. In favorable conditions, that helps. In many homes, it is not enough to keep levels below 4.0 pCi/L reliably.
The core limit of a passive system is its dependence on conditions you cannot control. Temperature differences, wind, seasonal pressure swings, and HVAC operation all change how much natural suction the pipe makes. On less favorable days or seasons, the pipe may do very little. Read more on the difference between active and passive radon mitigation and why most pros recommend converting to active when levels are high.
Should You Test a New Home Before or After Moving In?
Test after you move in and live in the home normally. An empty house with sealed windows and no occupants does not match the pressure and airflow of a lived-in home. Running HVAC, opening doors, cooking, and using fans all shape how radon builds up. Testing in real living conditions gives a more accurate read.
The EPA recommends testing the lowest level you use regularly. For a new home with a finished basement used as living space or an office, put the test there. A test in an upstairs bedroom would miss the concentration where a family member spends hours each week downstairs. For placement details, see this guide to where to place a radon test.
For most new homeowners, a professional short-term test returns results in a few days and gives a reliable baseline. Between 2.0 and 4.0 pCi/L, the EPA recommends considering action. Above 4.0 pCi/L, the recommendation is to mitigate.
What Happens If a New Home Tests High for Radon?
A high result in a new home is not a construction defect. It reflects the geology beneath the lot, which no builder can change. The practical response is simple. Upgrade from passive to active if the builder installed passive piping, or install a full active system if no passive parts exist.
Sub-slab depressurization is the most common and effective method for slab homes. A fan connects to the existing pipe, or a new suction point goes through the slab. The fan then draws soil gas out continuously and vents it above the roofline before it builds up indoors. Active systems consistently outperform passive ones, and effectiveness can reach up to 99% in many cases, per New York State Department of Health data, though results depend on the home.
If your new home has a crawl space, the approach shifts to crawl space radon mitigation with sub-membrane depressurization. That means sealing the crawl space floor with a vapor barrier and pulling suction beneath it. Homes with combination foundations may need parts of both.
After any install, a post-mitigation retest is essential. Radon 1 includes verification testing with documentation on every job, so you get a written record that levels dropped. That documentation also helps if you sell the home later.
Does Radon-Resistant Construction Eliminate the Need to Test?
Radon-resistant construction lowers the chance of high levels and makes mitigation easier if you need it. It does not remove the need to test. The EPA states plainly that RRNC features do not guarantee low levels, and that testing after occupancy is still recommended.
The value of RRNC is mostly the infrastructure it provides. With a passive pipe already in place, converting to active is faster and less invasive than a full retrofit. Builders who include RRNC give future homeowners a real advantage. But that advantage only pays off if the homeowner follows up with a test to see whether the passive system performs.
Frequently Asked Questions
Do new homes have lower radon levels than older homes?
Not necessarily. Radon levels depend on soil composition and foundation design, not the age of the home. A new home built on high-radon geology can test just as high as an older structure in the same area. The only way to know your actual level is to test.
If my builder included a radon pipe, is my home protected?
A passive radon pipe provides some protection under favorable conditions, but it does not guarantee low radon levels. Passive systems rely on natural pressure differences that vary with weather and season. If your test comes back above 4.0 pCi/L, adding a fan to activate the system is typically a straightforward and affordable upgrade.
When should I test a new home for radon?
Test after you move in and the home is being occupied normally, with the HVAC running and your typical household routines in place. The EPA recommends testing the lowest livable level of the home. If you plan to use a basement regularly, that is where the test should go.
What does it cost to upgrade a passive system to an active one?
Costs vary by home design, foundation type, and whether the passive pipe was already positioned in a workable location. Radon 1 provides estimates that include materials, labor, and post-installation verification testing so there are no surprises. You can call (615) 257-9818 for a specific quote based on your home.
How long does radon mitigation take in a new home?
Most residential installations are completed in a single day. If an existing passive pipe is in a good location, converting it to an active system is often a shorter process than a full retrofit from scratch. How long radon mitigation takes depends on foundation type and system complexity.
If your new home has not been tested yet, or if you have a passive system and want to know how it is actually performing, schedule a professional test with Radon 1. Radon 1 is NRPP and AARST certified, with more than 20,000 systems installed across Tennessee, Kentucky, Alabama, Georgia, and North Carolina. Every installation includes post-mitigation verification testing to confirm it’s working. Call (615) 257-9818 to get started or visit radon1.com to learn more about testing and mitigation options for your home.