Before you finish your basement, test for radon
Written and reviewed by Bill Dahlstrom, Illinois radon mitigation license RNM2018212 · Updated
Test before the drywall goes up. If your number is high, it's much easier to plan the system while the ceilings, walls, and floors are still open.
Why test before you finish the basement?
The pipe route, sump access, ceilings, and where the pipe goes outside are all easier to work out before the finished walls go in. The CDC recommends testing before major renovations when you can. A short talk before the remodel can save you an awkward pipe route later.
Already have a radon system, and the pipe or fan is in the way? We may be able to move or reroute it instead of tearing it out and starting over.
What is harder once the basement is finished?
Finished ceilings leave fewer clean places to run pipe.
Built-ins can block corners, walls, and access to the utility area.
New flooring makes drilling and sealing more of a mess.
A hidden sump is harder to reach, both for radon work and for pump service.
A tight utility room leaves fewer good choices.
If your test is high
Bill can come out, look at your home, and lay out your choices before the remodel goes on. The goal isn't to make the project bigger. It's to plan the system while you can still get to everything.
If your basement is already finished
You still have options. A radon system can still go into a finished home. It just takes more care with the pipe route, sump access, where things go outside, and the finished rooms you want to keep as they are.
To see how install day goes, read what to expect during a radon mitigation install.
What to ask before you close the walls and ceilings
Where is the sump pit?
Can you get into the crawl space?
Where could the pipe run cleanly?
Where would an outside fan make sense?
Will anything block access later?
Still need to test?
Our testing guide shows where to get a free or $8 county kit, which kind of test to use, and what your number means.
Read the radon testing guideMore guides are in our Radon Resource Center.
“Top notch job. Bill and his crew installed a 2 suction point system, 1 point in the basement and 1 in the crawlspace addition. Along with the suction points, they laid down a vapor barrier in the crawl space, a new sump pump cover and caulked any cracks in the…”
Basement planning questions
Testing before the remodel, sump sealing, how the pipe gets routed, and how long the install takes.
How long does a typical radon mitigation install take?
Most residential installs are completed in a single visit, often a few hours once the plan is set. Bill looks at the home first so materials and routing are right. Real estate closings get scheduled around the calendar when you tell us the date early.
Is sealing the sump necessary for radon mitigation?
Often yes. An open sump is a common soil-gas path. We typically seal the sump with a lid that still allows pump service and access. Sealing alone is not a full mitigation system, but a proper lid is usually part of a good design when a sump is present.
Will the exterior pipe look bad on my house?
We plan routing carefully. Where the layout allows, pipe may go through a garage attic or interior chase and out the roof. When the cleanest path is outside, it goes on a side or rear elevation and is finished to read more like a downspout than a mistake on the front of the home.
Should I test for radon before finishing the basement?
Yes. Testing before drywall and ceilings makes routing and planning easier if mitigation is needed. Remodeling can also change how the lower level is used. If levels are elevated, handle mitigation with the finish plan in mind.
Can I just seal the cracks and the sump instead of installing a system?
Sealing by itself is not a fix. Illinois guidance does not recommend sealing alone because it has not been shown to lower radon levels significantly or consistently; soil gas finds the next opening. Sealing matters as part of an active system, where the sump lid and openings are closed so the fan’s suction stays under the slab instead of pulling room air.
Helpful official radon resources
Last reviewed by American Radon Systems: June 2026
- CDC testing for radon in your home
Includes guidance on testing before major renovations and after work is completed.
- EPA explanation of the 4.0 pCi/L action level
Federal guidance on when EPA recommends fixing a home.
- Illinois IEMA-OHS Radon Program
Illinois radon program information for homeowners.
Reviewed by Bill Dahlstrom, Illinois radon mitigation license RNM2018212.
Planning to finish your basement?
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