Guide · checked Nov 13, 2026

Radon and crawl spaces

Radon is a gas from the soil, and a crawl space sits right on the soil. If you're about to spend thousands sealing one, test for radon first: it's cheap or free, and it changes what you should ask for.

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Radon zones around Chattanooga

Zones are county-wide predictions, not readings for your house. The EPA says every home should be tested regardless of zone. TDEC says that in Tennessee, 1 in 4 homes that request its free test kit test above 4 pCi/L, and that levels needing immediate action have been found in every county.

Get a test kit

• Tennessee: TDEC's Tennessee Radon Program sends free test kits, including the lab. It says to run the test for 3 to 5 days and mail it back right away.
• Georgia: UGA's radon program sells a kit for $15, including shipping and the lab analysis.
• The EPA recommends action at 4 pCi/L or above and suggests considering it between 2 and 4.

Is encapsulation radon mitigation?

Not by itself. The EPA's Consumer's Guide to Radon Reduction says the most effective fix in crawl space homes is sub-membrane suction: a plastic sheet over the crawl space floor with a vent pipe and fan pulling radon from under the sheet and venting it outside. It reports 50% to 99% reductions. Natural crawl space ventilation reduced radon 0% to 50%. A sealed liner is part of sub-membrane suction, but without the pipe and fan it isn't the same system.

If you test high and plan to encapsulate, ask the crawl space company whether it installs radon systems or can leave the liner ready for one (and who will do it). TDEC recommends hiring a certified radon mitigation professional (listed by NRPP or NRSB). The EPA's guide says to test after installation to make sure the system works, and to retest at least every two years.

Order of operations

1. Test for radon (free in Tennessee, $15 in Georgia).
2. Fix any water getting in (drainage first).
3. If you encapsulate and radon is high, combine the liner with a sub-membrane suction system by a certified pro.
4. Re-test after the work.