Radon Testing in Fresno

Fresno sits in the southern San Joaquin Valley on a broad alluvial plain where the geology beneath older neighborhoods can create conditions that allow radon, a colorless, odorless radioactive gas, to migrate upward into living spaces without any visible warning. The valley’s clay-heavy soils and the prevalence of slab-on-grade and raised-foundation construction across Fresno’s mid-century housing stock both play a role in how radon enters a home. If you’re buying, selling, or simply want to know what your family is breathing, a professional radon test is the only way to find out.

Why Fresno Properties Warrant a Closer Look at Radon

The San Joaquin Valley’s subsurface is geologically complex, layers of alluvial sediment, decomposed granite washed down from the Sierra Nevada, and pockets of uranium-bearing rock contribute to naturally occurring radon production in the soil. While California as a whole is not classified as a high-radon state the way parts of the Midwest or Appalachia are, the EPA’s own mapping places portions of the Central Valley in Zone 2 (predicted average indoor radon levels between 2 and 4 pCi/L), meaning a meaningful percentage of untested homes could be at or above the EPA action level of 4 pCi/L.

Fresno’s housing stock adds another layer of consideration. Neighborhoods developed in the 1940s through the 1970s frequently feature concrete block foundations, older crawl spaces with minimal vapor barriers, and construction practices that predate modern radon-resistant building techniques. Homes in those eras were not built with sub-slab depressurization in mind, which means radon pathways, cracks in slabs, gaps around utility penetrations, porous block walls, are more common than in newer construction.

Our Radon Testing Process in Fresno

Arch Environmental Group uses continuous electronic radon monitors rather than passive charcoal canisters for most residential and commercial tests. Continuous monitors log radon concentrations hour by hour over the test period, which is typically 48 hours for a short-term test conducted under closed-house conditions. That granular data matters: it can reveal whether elevated readings are consistent throughout the day or spike during specific periods, which helps distinguish a soil-gas intrusion problem from an anomalous reading.

For real estate transactions, which drive a significant share of radon testing requests in Fresno’s active housing market, we follow EPA and state protocols for closed-house testing, place monitors at the lowest livable level of the home, and provide a written report with the average concentration, hourly data, and a plain-language interpretation of what the numbers mean. If results come back above 4 pCi/L, the report will note that mitigation should be evaluated; we do not perform mitigation ourselves, so our findings are never influenced by a financial interest in the outcome.

For property managers or landlords overseeing multiple units, we can coordinate multi-unit testing schedules to minimize disruption to tenants while ensuring each unit is tested under proper closed-house conditions.

Reaching Fresno from Kingsburg

Arch Environmental Group is based in Kingsburg, roughly 20 miles south of Fresno on Highway 99. That puts us well within a practical service radius for properties throughout Fresno and the surrounding communities. Scheduling is handled directly by phone at (559) 296-2088, and we work with property owners, real estate agents, and commercial clients to find appointment windows that fit the 48-hour closed-house testing requirement without disrupting a transaction timeline.

Equipment & Methods We Use for Radon

Continuous radon monitors provide a level of documentation that passive tests cannot. Because the device records concentration data at set intervals throughout the test, the final report is not a single averaged number from a lab, it is a time-series record that can be reviewed by buyers, sellers, and their agents. This is increasingly requested in real estate transactions where one party wants confidence that the test was not compromised by open windows or HVAC manipulation during the testing period. The monitor’s internal tamper log and the hourly data together provide that assurance.

For larger commercial properties or buildings with multiple HVAC zones, we assess the structure before recommending a testing strategy, since a single monitor placed incorrectly can miss localized radon entry points in a complex floor plan.

Local Note

Fresno’s older residential neighborhoods, particularly those developed in the postwar decades when tract construction moved quickly across the valley floor, often have slab foundations poured directly on native soil with little or no vapor barrier between the concrete and the ground. Over decades, those slabs develop hairline cracks that are invisible to the eye but serve as direct conduits for soil gas. In the Central Valley’s dry summers, the pressure differential between the warm outdoor air and cooler indoor air can actually draw soil gas upward more efficiently than in cooler, wetter climates. That means a home that tested fine in a wet winter may show higher radon concentrations if tested during a Fresno summer, a seasonal variable worth understanding when interpreting results.

If you are ready to schedule a radon test for your Fresno home or commercial property, call Arch Environmental Group at (559) 296-2088. We will walk you through the testing protocol, what to expect during the 48-hour window, and how to read your results when the report is complete.