Glossary · Health & indoor air
Radon
Also called: radon gas · radon-222 · radon level · radon levels
A natural radioactive gas from uranium in soil and rock that can build up in homes; long-term exposure raises the risk of lung cancer.
What it means
You can't see, smell or taste radon, so testing is the only way to know your level. It enters through foundation cracks, sumps, floor drains and gaps around pipes, drawn in by the stack effect and depressurization. Canada and the US use different units and action levels (see radon units).
Why it matters in an audit
Air sealing and ventilation changes affect radon, so a radon test before or after upgrades belongs in any audit, and fixing high levels usually costs about as much as other common home repairs.
Typical numbers
Reference values with their sources. Your auditor’s report gives the figure for your own house.
| What | Value | Source |
|---|---|---|
| US EPA action level | 4 pCi/L (EPA rounds it to 150 Bq/m³); consider fixing between 2 and 4 pCi/L | epa.gov ↗ |
| Average US levels (EPA) | About 1.3 pCi/L indoors (≈ 50 Bq/m³); about 0.4 pCi/L outdoors (≈ 15 Bq/m³) | epa.gov ↗ |
| US homes with elevated radon (EPA, 2009) | Nearly 1 in 15 | nepis.epa.gov ↗ |
In the United States
EPA's action level is 4 pCi/L; a short-term test is a common first screen, followed by a long-term or second short-term test before deciding.