Radon is the pollutant that breaks every intuition about house problems: colorless, odorless, tasteless, undetectable by any sense or symptom, geological rather than mechanical in origin, and, by the public-health accounting, the second-leading cause of lung cancer after smoking. Radon testing basics reduce to one sentence, the only diagnosis is a test, and the good news completes it: elevated homes are fixed reliably and affordably. This reference covers the gas, the testing tiers, the numbers, and the fix.
What it is and how it enters
Radon is a radioactive gas born from uranium’s decay in soil and rock, seeping upward everywhere and accumulating wherever a structure concentrates it. Houses inhale it through the foundation’s openings, slab and wall cracks, floor-wall joints, sump pits, utility penetrations, and exposed crawl space soil, drawn by the stack effect’s gentle vacuum on the lowest levels, which is why basements and ground floors read highest and why winter, with the house closed and the stack effect strongest, reads above summer. The geological lottery is fine-grained: radon zones map regions, but neighboring houses on the same street test an order of magnitude apart, so maps guide policy while only tests diagnose homes, every home, slab-on-grade included, the no-basement exemption being folklore.
Testing: the tiers and the number
Short-term tests, charcoal canisters and similar, run 2 to 7 days under closed-house conditions (windows shut, normal door use) on the lowest lived-in level: the cheap screen, from hardware stores and often free through state programs. Long-term tests, alpha-track detectors running 3 to 12 months, average the daily and seasonal swings into the number that actually characterizes exposure, the better basis for a mitigation decision on a borderline screen. Continuous monitors, the digital tier, track levels live, useful for before-and-after mitigation proof and for the curious, and standard equipment in real-estate testing, where protocols guard against the opened-windows problem. The decision number: the EPA action level of 4 picocuries per liter, mitigation recommended above it, considered between 2 and 4, with the honest framing that the level is a management threshold on a no-safe-dose curve rather than a line between safe and dangerous. Retesting belongs on the calendar after any result near the line, after major air-sealing or renovation work that changes the house’s breathing, and every couple of years in mitigated homes as the system audit.
Mitigation: the fix that works
The standard cure is active sub-slab depressurization: a hole cored through the slab into the gravel or soil beneath, sealed around a vertical pipe, an inline fan running continuously, and the exhaust terminated above the roof, the assembly reversing the pressure so soil gas flows to the pipe instead of the house, routinely bringing elevated homes well below the action level for the cost class of a mid-range appliance installation. Variants cover the foundation types: sump-pit suction where the pit offers access (with a sealed lid doing double duty against moisture), drain-tile suction, membrane-and-suction systems over encapsulated crawl spaces (radon and moisture mitigation sharing the same plastic), and multiple suction points for stubborn slabs. The supporting cast: sealing accessible entry routes (helpful, insufficient alone), the fan’s u-tube manometer on the pipe as the always-on system gauge (level fluid means a dead fan, the one maintenance check), and certified mitigation contractors as the trade norm, with a post-installation test as the proof. Passive stub systems in new construction, the pipe roughed in awaiting a fan, activate cheaply when the first test asks.
The bottom line
Radon is invisible geology taxing the lowest floor, the only diagnosis is a test, and the test costs less than dinner: screen short-term, confirm long-term near the line, act at 4, and fix with a fan and a pipe that pull the soil’s gas around the house instead of through it. Then glance at the manometer now and again, because the entire system’s health is one column of colored fluid.