20 min read
Radon system
Living with a radon mitigation system, from the manometer to maintenance and retesting.
Read the guideOwning and renting6 min read
Radon testing in new homes: why, when and what to do with the result
Short answer
Radon testing in new homes matters because any home can have a radon problem, new or old, and how much radon a house collects cannot be known until it is built. EPA recommends testing every new home after occupancy, even one built with radon-resistant features, and if the result is 4 pCi/L or more, adding a fan to the passive system and retesting.
Next step: check the rules where you rent or let. Radon rules for rentals by state
Key takeaways
- New and old homes alike can have radon problems; any home may.
- A house's radon level cannot be known until it is built, so the test comes after construction.
- Every new home should be tested, even one built with radon-resistant features.
- At 4 pCi/L or more, activate the passive system with a fan, then retest, and test at least every two years after.
- Testing standards for new construction now include a radon test after the house is finished.
Why a new home still needs a radon test
Radon testing in new homes follows the same method as in any home, but it answers a question no one can answer in advance. Any home may have a radon problem, including new and old homes, well-sealed and drafty homes, and homes with or without basements. Local radon levels may also differ from the county map, and the amount of radon that will build up in a home cannot be determined until it is built.
Agency estimate
Nearly 1 in 15
U.S. homes estimated to have an elevated radon level (4 pCi/L or more), according to EPA
Even radon-resistant features are not a guarantee. Every new home should be tested after occupancy even if it was built radon-resistant, because the passive features reduce radon but may not bring every house below 4 .
When to test a new house
The test comes after people move in: every new home should be tested after occupancy, as soon as possible. Builders in the Indoor airPLUS program go further and test all homes prior to occupancy. Either way, the best way to determine a home's radon level is to test it after occupancy.
| When | For |
|---|---|
| As soon as possible after you move in | Every new home, even one built radon-resistant |
| Prior to occupancy | Homes built in the Indoor airPLUS builder program |
| After construction is complete | Homes built to the ANSI/AARST RRNC standard (10/22 revision) |
| After a fan is added to a passive system | Confirming the active system works |
| Every two years after, and after major renovations | Every home with a system |
If you are buying a newly built home, ask whether radon-resistant features were used and whether the home has been tested.
How to test a new home for radon
The method is the one for any home. Short-term or kits can be bought by mail or at local hardware stores; stay in the home between 2 and 90 days, and long-term tests longer than 90 days. All radon tests should run at least 48 hours.
Choose a test
A short-term test for a quick answer, or a long-term test for the year-round average.
Place it on the lowest lived-in level
At least 20 inches above the floor, away from drafts, high heat, high humidity and exterior walls, in a room used regularly but not a kitchen or bathroom.
Keep the house closed
For a short-term test, windows and outside doors closed except for normal entry and exit, from 12 hours before a 2- or 3-day test.
Send it in and read the result
Results usually come back within a few weeks.
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| Test | How long it runs | What it is for |
|---|---|---|
| Short-term test | Stays in the home from 2 to 90 days, depending on the device, and for a minimum of 48 hours. | A faster screening result. Because radon levels vary from day to day and season to season, it is less likely than a long-term test to tell you the year-round average. |
| Long-term test | Stays in the home for more than 90 days. | It is more likely than a short-term test to tell you the home's year-round average radon level. |
| Continuous monitor | Logs readings for the whole test, run as a short-term or a long-term test under the same durations in EPA guidance. | Logs a graph over time, so you can see trends and spot anomalies rather than a single number. |
Every step, from to reading the lab report, is on radon testing.
What the new construction standards say about testing
Testing is now written into the standards builders follow. The 10/22 revision of ANSI/AARST RRNC, the standard for roughing in radon control components in new 1 and 2 family dwellings and townhouses, adds a requirement for radon testing after construction is complete. ANSI/AARST CCAH includes minimum requirements for verifying whether radon is below the national and for activating the radon control system if required.
| Standard | What it covers |
|---|---|
| ANSI/AARST RRNC-2020 (Rev. 10/22) | Rough-in of radon control components; the revision adds radon testing after construction is complete |
| ANSI/AARST CCAH-2020 (Rev. 5/23) | Verifying whether radon is below the national action level and, if required, activating the radon control system; its 2023 update improves initial testing after a home is built |
Whether a builder in your area must follow them depends on local code. The features themselves are on radon-resistant new construction.
What to do with a new home's result
EPA recommends fixing a home when the radon level is 4 pCi/L or higher. EPA recommends considering a fix when the level is between 2 and 4 pCi/L. For a new home the next step depends on whether it has a passive system.
| Result | With a passive radon system | Without one |
|---|---|---|
| 4 pCi/L or more | Activate the system with an in-line fan installed by a credentialed or licensed contractor, then retest | Confirm the result, then fix with a mitigation system |
| 2 to 4 pCi/L | Consider adding the fan; the passive system makes the upgrade easy | Consider fixing |
| Below 2 pCi/L | Keep the system as it is; retest every two years and after major renovations | Test again sometime in the future and after renovations |
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1Step 1: Take a short-term test.
- Below 4 pCi/LEven if your test result is below 4 pCi/L, you may want to test again sometime in the future.
- At or above 4 pCi/LIf your result is at or above 4 pCi/L, take a followup test to be sure.
2Step 2: Follow up with either a long-term test or a second short-term test.
- Long-term testFor a better understanding of your year-round average radon level, take a long-term test.
- Second short-term testIf you need results quickly, take a second short-term test. If your first short-term test result is more than twice EPA's 4 pCi/L action level, you should take a second short-term test immediately.
3Step 3: Decide whether to fix your home.
- After a long-term testFix your home if your long-term test result is 4 pCi/L or more.
- After a second short-term testConsider fixing your home if the average of your first and second test is at or above 4 pCi/L.
A new home with a passive radon system
A passive system is built to be upgraded. If high levels are found, a fan can easily be installed as part of the system for further reduction, and at 4 pCi/L or more a vent fan can easily be added to make it an active system. Virtually all homes with an active system have radon levels below 4 pCi/L.
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Typical radon reduction, EPA
Basement and slab-on-grade homes
- Subslab suction (subslab depressurization)50 to 99 percentWorks best if air can move easily in material under slab.
- Passive subslab suction30 to 70 percentMay be more effective in cold climates; not as effective as active subslab suction.
The upgrade is usually a small job: the passive system typically includes a junction box in the attic to make the future installation of the fan easy. A rough-in alone is different: if a builder only roughs in a system, the home buyer should be told the home does not have a functioning system. Living with the system is covered in the passive radon system guide.
Buying a newly built home
Check the area
Find out whether you are buying in a high radon area; homes in Zone 1 should be built with radon-resistant features.
Ask the builder
Whether radon-resistant features were used, and whether the home has been tested.
Ask for the features if they are missing
Published model standards and architectural drawings help to explain the techniques to your builder.
Test after you move in
Even with the features, test after occupancy.
Activate if needed
At 4 pCi/L or more, call a local radon mitigator to install the in-line fan.
| Zone | Predicted average indoor level |
|---|---|
| Zone 1 | May be greater than 4 pCi/L |
| Zone 2 | May be between 2 and 4 pCi/L |
| Zone 3 | May be less than 2 pCi/L |
Homes with elevated levels have been found in all three zones, so the zone tells you about the area, not the house. Your county's zone is on the radon map.
Retesting a new home over time
A first test is not the last. Retest after activating a system, then every two years and whenever major renovations or alterations are made. If you start using a lower level, such as a basement, retest on that level, because major renovations and new uses can change the radon level in any home.
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Day of installation
The system goes in
Keep the fan running at all times: it must run continuously for the system to work correctly.
No sooner than 24 hours
Earliest post-mitigation test
Test no sooner than 24 hours after your system is in operation with the fan on, if it has one.
Within 30 days
Post-mitigation test done
A two- to seven-day measurement is recommended, and EPA recommends an independent follow-up radon measurement as well as any test the contractor runs.
At least every two years
Retest
Retest your home at least every two years to be sure radon levels remain low.
Test conditions: Windows and doors must be closed 12 hours before and during the test, except for normal entry and exit. Not drawn to scale.
After a remodel. After you remodel, retest in the lowest lived-in area to make sure the construction did not reduce the effectiveness of the radon reduction system.
New home radon testing questions
Do new homes have radon?
They can. Any home may have a radon problem, new or old, and the level cannot be known until the home is built and tested.
Do I need a radon test for a new construction home?
Yes. Every new home should be tested after occupancy, even if built radon-resistant.
When should a new home be tested for radon?
After you move in, as soon as possible. Builders in the Indoor airPLUS program also test before occupancy.
My new home has a radon pipe. Do I still need to test?
Yes. A passive pipe reduces radon but may not bring the level below 4 pCi/L; only a test shows the level.
What if my new home tests high?
If it has a passive system, have a fan installed to activate it and retest. If not, confirm the result and have a mitigation system installed.
Who pays to activate a passive system in a new home?
That depends on your contract. Ask your builder before closing whether radon is covered by the warranty or contract.
Can I test a new home before I move in?
Builders in the Indoor airPLUS program test prior to occupancy, but a test after you move in is still the one that counts.
Should a new home be retested?
Yes: after any fan is added, every two years, after major renovations, and if you start using a lower floor.
Questions people ask
Do I need a radon test for a new home?
Yes. EPA and the Surgeon General recommend testing every home below the third floor, whatever its age, foundation or location, because radon cannot be seen, smelled or tasted, and a test, which is inexpensive and takes only a few minutes of your time, is the only way to know a home's level.
When should a new home be tested for radon?
Test now if your home has never been tested, since EPA recommends testing all homes below the third floor. Then test again after moving into a new home, before and after major renovations, within 30 days of installing a radon system and every two years after, and when you buy or sell.
Should a new house with a radon system still be tested?
A passive radon system is the set of radon-resistant features built into a new home, with a vent pipe from beneath the slab through the roof and no fan. EPA says every new home should be tested after occupancy, and if levels are still in excess of 4 pCi/L, a qualified mitigator should add a vent fan.
Owning and renting
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