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Radon in Crawlspace Homes: Testing and Fixes That Work
Many people assume a house raised on a crawlspace is protected from radon because there's air between the soil and the floor. It isn't automatically. This guide explains how radon moves in crawlspace homes and what EPA says works to reduce it.
How radon gets in
Radon comes from uranium breaking down in soil and rock (SC DES). In a crawlspace home, the earth floor is exposed. Air in the house is usually at slightly lower pressure than the soil gas, so radon can be drawn up from the dirt into the crawlspace and then into living space through floor penetrations, ductwork and gaps.
Testing a crawlspace home
- Test in the lowest lived-in level, which for a crawlspace house is usually the main floor. Don't put the test in the crawlspace itself.
- If part of the house is on a slab or basement and part on a crawlspace, that's more than one foundation. SC DES, citing EPA, recommends more than one test in that case.
- Follow EPA's two-step method before deciding. Our radon testing checklist covers the details.
Fix options EPA describes for crawlspaces
| Method | How it works | EPA notes |
|---|---|---|
| Submembrane suction | High-density plastic sheet over the earth floor, with a vent pipe and fan drawing radon from under the sheet and venting it outdoors | "When properly applied, the most effective way to reduce radon levels in crawlspace homes." EPA's table lists typical reductions of 50 to 99 percent. |
| Active crawlspace depressurization | A fan draws air directly from the crawlspace | Less favorable; generally doesn't work as well, and needs attention to combustion-appliance backdrafting and sealing the crawlspace from the house. |
| Crawlspace ventilation (passive or fan) | Opening or adding vents, or blowing air through the crawlspace | EPA's table lists 0 to 50 percent for natural ventilation; it can also add heating and cooling losses. |
Source: EPA, A Consumer's Guide to Radon Reduction (2016). Reduction ranges are EPA's general figures, not a guarantee for any home.
Is encapsulation the same thing?
Not necessarily. Crawlspace encapsulation is usually sold as a moisture-control upgrade. A liner by itself, without suction underneath, is not the same as submembrane suction. If you're encapsulating anyway, ask whether a suction point can be included so the liner can double as a radon membrane. More detail in how radon mitigation systems work.
After the fix
SC DES recommends a short-term test 24 hours to 30 days after the system starts, and retesting mitigated homes at least every two years. Check that the membrane stays sealed, especially after anyone has worked in the crawlspace.
Have a crawlspace home in the Upstate with a high result? Learn about radon mitigation options, or book radon testing first.
References: EPA, A Consumer's Guide to Radon Reduction (2016); SC DES Radon Program.
Radon services in Greenville
Quick answers
Can a crawlspace house have high radon?
Yes. Soil gas can rise from bare earth under the house into living space. EPA's Consumer's Guide covers crawlspace homes specifically.
What is the best radon fix for a crawlspace?
EPA calls submembrane suction, a sealed plastic sheet over the soil with a fan drawing air from beneath it, the most effective way to reduce radon in crawlspace homes when properly applied.
More radon guides
- Is Radon a Problem in Greenville County, SC?
- How to Test Your Greenville Home for Radon
- What Radon Mitigation Typically Costs in Upstate SC
- Radon Tests When Buying or Selling a Home in Greenville
- Radon Health Risks: What Upstate Homeowners Should Know
- What Radon Levels Mean: The EPA 4 pCi/L Action Level Explained
- How to Choose a Radon Mitigation Company in Greenville, SC