Should you test for radon before finishing your basement?

Yes. The EPA says to test before you start and again when you're done, because a remodel can change radon levels. Answer three quick questions to see your next step.

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Why test for radon before finishing a basement?

Radon is a gas that comes up from the ground, and the basement is usually where it gets in. The EPA says that if you're turning an unfinished basement into living space, it's especially important to test before you begin, and to test again after the work is done, because major renovations can change radon levels. If a fix is needed, the EPA says it's generally less expensive to put in a radon system before or during the project than afterward.

Question 1. Where are you with the basement?

Why we ask: it's easiest to plan for radon before the walls go up.

• Still planning: test the basement now, before anything is built.
• Work underway: test now if you can, and tell your contractor you're checking for radon before walls and ceilings close in.
• Already finished: test the basement now. It's living space, so it's the level to test.

Question 2. Do you already have a radon system?

Why we ask: finishing around a system changes what you need to do.

• Yes, with a fan: keep the system's label and its warning gauge where you can see them, and leave the fan running. The EPA says to ask your radon contractor whether a basement remodel could void any warranty before you start. Retest when the project is done.
• A pipe with no fan (a passive system): test the basement. If the level is high, a certified contractor can often add a fan to the pipe that's already there.
• No system, or not sure: test first. The result tells you whether you need to do anything.

Question 3. What did your radon test say?

Why we ask: the number decides your next step.

• Not tested yet: see how to test for radon. Wisconsin's radon program says to test the lowest level where you spend at least seven hours a week. Once the basement is finished, that's usually the basement.
• Under 4 pCi/L: the EPA suggests thinking about a fix between 2 and 4. Test again after the project is finished.
• 4 pCi/L or higher: Wisconsin's radon program says to do a second test. If the two results average above 4, it recommends a fix. Request a free quote below, ideally before the walls close in, and we'll look for a certified radon contractor who serves your area.

Have a number and not sure what it means? Try the radon level checker.

Ready to get it fixed?

Tell us your ZIP code, your result, and that you're finishing the basement. We'll look for one NRPP or NRSB certified radon contractor who serves your area, and your request goes to that one contractor, never a list.

Request a free quote

Prefer to call? (414) 775-3622. Call or leave a message.

• Certified contractors only (NRPP or NRSB). Free, no obligation.
• Wisconsin doesn't require radon contractors to be licensed or certified, so Wisconsin's radon program recommends NRPP or NRSB certified professionals. That's who we look for.
• Wisconsin Radon Help connects homeowners with certified radon contractors. We don't do the testing or the fix ourselves.
• Sources: US EPA's guide to buying a new home and Consumer's Guide to Radon Reduction, and the Wisconsin Department of Health Services radon program. Read November 2026.