Radon Testing & Exposure Assessment

A standard short-term radon test runs for a minimum of 48 hours. For real estate transactions, 48–72 hours is typical. Long-term tests run for 90 days or more to establish an annual average. We can usually place the monitor within 1–2 days of scheduling.

California’s statewide average is below the EPA action level, but radon levels vary by location and individual home. Parts of the Bay Area—particularly areas with certain soil and rock formations—can have elevated levels. Testing is the only way to know your home’s specific radon concentration.

If your home tests above 4.0 pCi/L, the EPA recommends radon mitigation. The most common solution is a sub-slab depressurization system, which draws radon from beneath the foundation and vents it above the roofline. These systems are effective, reducing radon levels by up to 99%.

The EPA recommends taking action when indoor radon levels reach 4.0 picocuries per liter (pCi/L) or higher. At this concentration, the EPA estimates the lifetime lung cancer risk from radon exposure is comparable to smoking half a pack of cigarettes per day. The EPA also recommends considering mitigation between 2.0–4.0 pCi/L. The average indoor radon level in U.S. homes is approximately 1.3 pCi/L.

Radon is produced by the natural decay of uranium in soil and rock. It moves through the ground as a gas and enters buildings through cracks in foundations, crawlspace openings, sump pits, gaps around pipes, and porous concrete blocks. The pressure difference between the soil and the interior of a building draws radon inward — particularly in homes with crawlspaces or slab-on-grade foundations.

Yes. Post-mitigation testing confirms the system is functioning as intended and that levels have dropped below the EPA action level. We recommend testing 24–30 days after mitigation system installation. If levels remain elevated, the mitigation contractor may need to adjust the system. Some California counties also require documentation of post-mitigation levels for real estate transactions.

Yes. Radon testing is increasingly common in California real estate transactions, particularly for homes with crawlspaces, basements, or slab foundations. Unlike asbestos, radon is not triggered by age of construction — any home in any neighborhood can have elevated levels. A 48–72 hour test during the inspection contingency period gives buyers actionable data before closing.