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Radon in the Basement vs the First Floor: Which Level to Test
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The rule
EPA says the test kit goes in the lowest lived-in level of the home. EPA's example: the basement if it is frequently used, otherwise the first floor. It should be in a room used regularly, like a living room, playroom, den or bedroom, but not the kitchen or bathroom.
The sources we opened do not give a typical difference between basement and first floor readings, so we do not give one. EPA does say radon can be a problem in homes with or without basements.
Cases that change the answer
| Your home | Where to test |
|---|---|
| Basement you use often (office, playroom, bedroom) | The basement (EPA). |
| Basement used only for storage | The first floor, says EPA. New Jersey counts an unfinished basement as livable even when it is not in use, so check your state's rule. |
| No basement (slab-on-grade or crawl space) | The lowest lived-in level. For a crawl space, see our crawl space guide. |
| Planning to finish the basement | EPA says to test the unfinished area before you begin, and test again after the work. |
| Basement with an unsealed sump pit | North Dakota says to test at least 10 feet from the pit. |
Sources: EPA Citizen's Guide, EPA Home Buyer's and Seller's Guide, New Jersey DEP, North Dakota DEQ.
Placement steps
- Pick a room you use regularly. Skip the kitchen, bathroom, laundry room and closets.
- Place the kit at least 20 inches above the floor, where it will not be disturbed, away from drafts, high heat, high humidity and exterior walls.
- Keep windows and outside doors closed as much as possible, and close them 12 hours before a 2 or 3 day test.
The full steps are in our test kit guide. Got a number? Use the result checker.
Ready to test your lowest level?
Testing is the only way to know your radon level. A mail-in kit is a low-cost way to start, and our guide shows how to place it so the result is reliable.
How to use a radon test kitBrowse radon test kitsCommon questions
Should I test the basement or the first floor?
EPA says to place the kit in the lowest lived-in level of the home. For example, test the basement if it is frequently used, otherwise the first floor.
What if I finish the basement later?
EPA says that if your living patterns change and you begin using a lower level, such as a basement, you should retest on that level. EPA also says to test an unfinished basement area before converting it to living space, and to test again after the work is done.
Does an unused unfinished basement count?
It depends on the state. New Jersey says an unfinished basement is a livable space even if it is not being used right now. EPA's own wording is the lowest lived-in level. Check with your state radon program.
Where in the basement should the kit go?
Away from drafts, high heat, high humidity and exterior walls, and not in the kitchen or bathroom. North Dakota adds that with an unsealed sump-pump pit in the basement, the test should be at least 10 feet from the pit.
Do I need to test every floor?
EPA and the Surgeon General recommend testing all homes below the third floor. The sources we opened give a single test location for a home: the lowest lived-in or livable level.
Related guides
- U.S. EPA: A Citizen’s Guide to Radon (EPA 402/K-12/002)
- U.S. EPA: Home Buyer’s and Seller’s Guide to Radon (EPA 402/K-24/001, March 2024 revision)
- New Jersey DEP Radon Program: Guidelines for Radon Testing in New Jersey
- North Dakota Department of Environmental Quality: Guidelines for Radon Testing in Residences
Free printable: Radon Test Day Checklist
EPA's testing steps in one page, plus what your result means. Download the one-page PDF now, or get it by email along with a short series of five helpful emails.