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EPA levels
The EPA action level for radon is 4 picocuries per liter. Pennsylvania's Department of Environmental Protection, citing EPA, advises installing a reduction system above it and asking contractors to guarantee a result below 4 pCi/L. One pCi/L equals 37 Bq/m³.
| pCi/L | Bq/m³ | Band |
|---|---|---|
| 1 | 37 | Below 2 |
| 2 | 74 | 2–4: consider fixing |
| 2.7 | 100 | 2–4: consider fixing |
| 4 | 148 | At or above action level |
| 5.4 | 200 | At or above action level |
| 8 | 296 | At or above action level |
| 10 | 370 | At or above action level |
| 20 | 740 | At or above action level |
Test before and after finishing
Finishing changes air pressure and leakage in a basement, so test before walls go up and again afterwards. A mitigation pipe is much easier to route before the ceiling is closed. The University of Georgia Extension, citing EPA, puts the average mitigation at about $1,500, with most between $900 and $3,000.
Moisture comes first
Finishing materials hide water problems until they become mold problems. Before framing, tape a 2 × 2 ft sheet of plastic to the slab and to a wall for two days: water under it means moisture is coming through the concrete; water on top means humid air is condensing. The first calls for drainage or sealing, the second for dehumidification. Keep a hygrometer in the finished space afterward and aim for the EPA's 30%–50% range.
- Extend downspouts several feet from the foundation.
- Slope soil away from the house.
- Use materials that tolerate moisture below grade: foam board, treated bottom plates, vinyl plank.
- Leave access to the sump pit, the radon fan and the main water shutoff.
Where basement moisture comes from
| Source | Sign | Usual fix |
|---|---|---|
| Rain and snowmelt | Wet floor edges after storms | Gutters, downspout extensions, grading |
| Groundwater | Water through cracks or under walls | Interior drain and sump pump |
| Humid outdoor air | Musty smell, sweating pipes in summer | Dehumidifier, keep windows shut on humid days |
| Vapor through concrete | Damp under a plastic test sheet | Vapor barrier, foam board, sealer |
| Plumbing and appliances | Local stains | Repair leaks, vent the dryer outside |
Short-term and long-term tests
Short-term tests measure for a few days and are useful for a first look or a home sale. Long-term tests run for more than 90 days and better reflect the year-round average, because radon levels vary with season and weather. If a short-term test reads at or above 4 pCi/L, follow up with a second test before deciding. Test in the lowest level you live in, which after finishing is usually the basement.
Common questions
At what radon level should I act?
The EPA recommends fixing homes at 4 pCi/L or above and considering it between 2 and 4 pCi/L.
How do I convert Bq/m³ to pCi/L?
Divide by 37. 148 Bq/m³ is 4 pCi/L.
Related calculators
Sources
- https://www.dep.pa.gov/OurCommonWealth/Pages/Article.aspx?post=89
- https://inspectandtest.net/guides/radon-mitigation-levels/
- https://fieldreport.caes.uga.edu/publications/C1065/