The Common Assumption — and Why It’s Only Partially True
Radon is often thought of as a northern or mountain-state problem — a concern for homes with basements in the Midwest and Northeast, not for South Florida’s slab-on-grade construction on flat limestone geology. This assumption has a factual basis: South Florida does have lower average radon levels than high-risk regions like Pennsylvania, Colorado, or Iowa. But “lower on average” does not mean “zero risk,” and the assumption that South Florida homes don’t need radon testing has led to a widespread failure to identify the elevated readings that do exist here.
What Radon Is and How It Enters Buildings
Radon is a naturally occurring radioactive gas produced by the decay of uranium and radium in soil and rock. It is colorless, odorless, and chemically inert — detectable only through measurement. When radon gas seeps from soil into a building and accumulates in indoor air, the radioactive decay products it generates can be inhaled and deposit in lung tissue, where their ionizing radiation damages cells. Radon is the second leading cause of lung cancer in the United States after cigarette smoking, responsible for an estimated 21,000 deaths annually according to the EPA.
Radon enters buildings primarily through pressure differentials between the soil and the building interior. Any opening in the lowest level of the structure — cracks in slabs, pipe penetrations, expansion joints — can allow soil gas to migrate inward. In buildings with basements, the entry pathways are extensive and below-grade. In South Florida’s slab-on-grade homes, the pathways are smaller but still present.
South Florida Geology and Radon
The Miami Limestone and Fort Thompson Formation that underlie most of South Florida are not high-uranium-content materials, which is why average radon readings here tend to be lower than in granite-rich regions. However, “average” masks meaningful variability. Specific soil types, fill materials used in construction, and proximity to phosphate deposits (historically present in Central Florida and portions of the southern state) can elevate radon generation rates locally. Individual home construction details — slab integrity, pipe penetrations, construction voids — determine whether whatever radon is generated actually enters the living space.
Testing Is the Only Way to Know
The EPA recommends testing all homes regardless of regional risk classification. The current action level — the concentration at which the EPA recommends mitigation — is 4 picocuries per liter (pCi/L). The EPA also recommends considering mitigation at levels between 2 and 4 pCi/L. Short-term tests (2–7 days, using charcoal canisters) and long-term tests (90+ days, using alpha track detectors) are both available. Long-term tests are more representative of actual annual exposure.
Testing is inexpensive — DIY test kits are available for $15–30 — and there is no rational argument for not testing. Florida’s real estate disclosure laws do not require radon disclosure, though some contracts include radon contingencies. Testing before purchasing a home is straightforward and provides actionable information.
Mitigation When Levels Are Elevated
If testing reveals radon above the action level, mitigation is effective and relatively affordable. The standard technique for slab-on-grade homes is sub-slab depressurization: a pipe is inserted through the slab into the soil beneath, and a small inline fan creates negative pressure under the slab, drawing radon-bearing soil gas out before it can enter the building. This system vents to the exterior, typically through the roof or wall. Professionally installed systems routinely reduce radon levels by 80–99 percent and cost $800–2,500 depending on the home’s construction.