Local & Regulations · 8 min read
EPA Radon Guidelines
What the EPA recommends about radon: the 4.0 pCi/L action level, the 2.0 pCi/L consideration threshold, testing protocols, and how the guidance is applied.
The federal guidance on radon is short, clear, and often misquoted. Understanding what the numbers actually mean makes it much easier to decide what to do with a test result.
The core recommendation is that all homes be tested, that homes at or above 4.0 pCi/L be fixed, and that homes between 2.0 and 4.0 pCi/L be considered for reduction.
The 4.0 pCi/L action level
The action level is not a safety threshold. It is a practical benchmark set at a concentration that mitigation technology can reliably achieve reductions below, at reasonable cost, in typical housing.
A home at 4.2 pCi/L is not dangerous in a way that a home at 3.8 pCi/L is safe. Risk is continuous. The threshold exists to give homeowners and professionals a consistent decision point.
The 2.0 pCi/L consideration level
Because risk exists below the action level, the EPA suggests considering mitigation between 2.0 and 4.0 pCi/L. Many homeowners in that range choose to mitigate, particularly when bedrooms are involved or when a household member smokes.
The World Health Organization recommends a reference level equivalent to roughly 2.7 pCi/L, which is lower than the US action level and reflects the same underlying understanding that no exposure is risk-free.
Testing protocol recommendations
The guidance covers how to test as well as when to act.
- Test the lowest level of the home that is lived in regularly.
- Maintain closed-house conditions for short-term tests, starting 12 hours before.
- Use a minimum 48-hour measurement period for short-term devices.
- Follow up an elevated short-term result with either a second short-term test or a long-term test.
- Retest after mitigation and every two years thereafter.
Guidance for real estate transactions
For transactions, the EPA describes protocols that emphasize test integrity: tamper-resistant devices, documented placement, and verified closed-house conditions.
This is the origin of the continuous monitor convention in real estate testing. The instrument records not just radon but the conditions under which it was measured, so a report is auditable rather than merely asserted.
New construction guidance
Federal guidance encourages radon-resistant new construction: a gravel layer beneath the slab, a vapor barrier, sealed openings, and a passive vent pipe from beneath the slab to above the roof.
These features add little to construction cost and make later activation with a fan quick and inexpensive. They do not eliminate the need to test a finished home.
Key takeaways
- 4.0 pCi/L is an action benchmark, not a safety line.
- The EPA suggests considering mitigation between 2.0 and 4.0 pCi/L.
- Closed-house conditions and correct placement are part of the guidance, not optional extras.
- Radon-resistant new construction features make later mitigation far simpler.