Radon is one of those topics that most Florida home buyers have either never heard of or assume doesn't apply to them. I get it - when people think of radon, they picture basements in the Midwest, not slab-on-grade homes in Tampa Bay. But here's the reality: Hillsborough County sits in EPA Radon Zone 1, the highest-risk category in the country, and parts of Central Florida have some of the most elevated indoor radon readings in the Southeast. I'm Barrett Henry with REMAX Collective, and I've walked buyers through radon testing and mitigation questions on plenty of transactions in the Brandon, Riverview, and Valrico areas. This guide covers what radon is, why Florida's geology makes it a real concern, how testing works during a home purchase, what the numbers mean, and what to do if levels come back high.
If you're in the middle of buying a home and wondering whether to add a radon test to your inspection list, this is the guide that answers that question. For the full picture on all the inspections you should consider, check out my home inspection checklist for Florida buyers.
Florida EPA Radon Zone Overview
The EPA classifies every county in the United States into one of three radon zones based on predicted average indoor radon levels. Zone 1 is the highest risk. Here's how that breaks down for Florida.
| EPA Zone | Risk Level | Predicted Avg. Indoor Radon | Notable Florida Counties |
|---|---|---|---|
| Zone 1 | Highest | Greater than 4.0 pCi/L | Hillsborough, Pinellas, Alachua, Citrus, Columbia, Dixie, Hernando, Lafayette, Leon, Levy, Marion, Miami-Dade, Orange, Polk, Seminole, Sumter, Union |
| Zone 2 | Moderate | 2.0 to 4.0 pCi/L | Brevard, Broward, Clay, DeSoto, Duval, Hardee, Highlands, Lake, Manatee, Osceola, Palm Beach, Pasco, Sarasota, St. Johns, Volusia |
| Zone 3 | Lowest | Less than 2.0 pCi/L | Charlotte, Collier, Escambia, Lee, Monroe, Okaloosa, Santa Rosa, St. Lucie, Walton |
The EPA action level is 4.0 pCi/L (picocuries per liter of air). Any home testing at or above this level should be mitigated, according to the EPA. The World Health Organization recommends action at 2.7 pCi/L - even lower. Both Hillsborough and Pinellas counties are Zone 1, which means the Tampa Bay area is in the highest-risk category in Florida.
What Is Radon and Why Is It Dangerous?
Radon is a colorless, odorless, tasteless radioactive gas that forms naturally when uranium in soil and rock breaks down. It's present in the ground virtually everywhere, but the concentration varies based on local geology. When radon seeps up from the ground and enters a building, it can accumulate to dangerous levels - and you'd never know it without testing because you can't see, smell, or taste it.
The danger is lung cancer. Radon is the second leading cause of lung cancer in the United States after smoking, responsible for an estimated 21,000 deaths per year according to the EPA. For non-smokers, radon is the number one cause of lung cancer. When you breathe air containing radon, radioactive particles become trapped in your lungs and damage tissue over time. The higher the concentration and the longer the exposure, the greater the risk.
This isn't a theoretical risk. It's a well-documented, scientifically established cause of cancer. And unlike many environmental hazards, radon exposure is something you can actually measure and fix.
Why Florida Has a Radon Problem
Most people associate radon with northern states that have basements cut into bedrock. Florida doesn't have basements - but it does have phosphate-rich geological formations that produce significant amounts of radon. Central Florida in particular sits on phosphate deposits that are some of the richest in the world. That phosphate contains uranium, which decays into radium, which decays into radon gas.
Hillsborough County was historically one of the largest phosphate mining regions in the country. Even though most active mining has moved south to Hardee, Manatee, and Polk counties, the underlying geology hasn't changed. The soil beneath homes in Brandon, Riverview, Valrico, and the greater Tampa Bay area still contains elevated levels of the minerals that produce radon. That's why Hillsborough County is classified as EPA Zone 1 - the same risk category as counties in Pennsylvania, Iowa, and other states known for severe radon problems.
Florida also has a unique construction factor: most homes are built on concrete slab foundations. While slabs don't have the below-grade living space of a basement, the slab itself sits directly on top of radon-producing soil. Any crack, gap, or penetration in that slab becomes a pathway for radon to enter the home.
How Radon Enters a Home
Radon moves from the soil into your home through any available pathway. Homes operate under slightly negative pressure relative to the surrounding soil - meaning the house literally pulls soil gases (including radon) in through the foundation. Here are the most common entry points.
- Cracks in the concrete slab - Even hairline cracks in a slab foundation can allow significant radon entry. Over time, concrete naturally develops shrinkage cracks, settlement cracks, and stress cracks - all of which create pathways.
- Gaps around plumbing penetrations - Wherever pipes pass through the slab (drains, water supply lines), there are small gaps between the pipe and the concrete. These gaps are direct conduits for soil gas.
- Construction joints - The joint between the slab and the foundation walls (the cold joint) is a common entry point, especially if it wasn't properly sealed during construction.
- Sump pits and floor drains - While less common in Florida slab homes, any opening in the floor that connects to the soil below creates a potential entry point.
- Porous concrete block walls - In Florida homes built with concrete block (CBS construction), the hollow cores of the blocks can channel radon from the soil up through the wall system.
- Well water - Radon can dissolve in groundwater, and when that water is used in the home, the radon is released into the air - particularly during showering, dishwashing, and laundry. This is primarily a concern for homes on private wells, not city water.
The takeaway: there's no such thing as a "radon-proof" house. New construction and older homes alike can have elevated radon. The only way to know is to test.
Radon Testing During a Home Purchase
If you're buying a home in Hillsborough County or anywhere in EPA Zone 1 or Zone 2 in Florida, I strongly recommend adding a radon test to your inspection checklist. The test is simple, inexpensive relative to the information it provides, and it can be done at the same time as your other inspections.
Short-Term Radon Tests
Short-term tests are the standard for real estate transactions because they produce results quickly. There are two main types used during home purchases.
- Continuous radon monitor (CRM) - An electronic device placed in the lowest livable area of the home for 48 to 96 hours. It takes hourly readings and produces an average. This is the preferred method for real estate transactions because it provides time-stamped data (which shows if someone tampered with the test by opening windows) and delivers results immediately when the device is retrieved. Most professional radon testers in Tampa Bay use CRMs.
- Charcoal canister test - A passive device that absorbs radon over 48 to 96 hours and is then sent to a lab for analysis. Results take several days after the canister is mailed. These are less expensive but provide less data than a CRM and can't detect tampering as easily.
Long-Term Radon Tests
Long-term tests (90 days to one year) provide a more accurate picture of a home's average radon level because radon concentrations fluctuate with weather, barometric pressure, soil moisture, and season. However, long-term tests aren't practical during a real estate transaction - you don't have 90 days to wait for results. They're more appropriate for homeowners testing their own residence over time.
Testing Conditions
For accurate results during a short-term test, closed-building conditions must be maintained. That means all windows and exterior doors must remain closed for at least 12 hours before the test begins and throughout the entire testing period. Normal HVAC operation is fine - in fact, running the AC is expected in Florida. The test device is placed on the lowest livable floor of the home, away from drafts, windows, and exterior walls.
Radon Test Costs in the Tampa Bay Area
| Test Type | Typical Cost | Turnaround Time | Best For |
|---|---|---|---|
| Continuous radon monitor (CRM) | $125-$200 | 48-96 hours + immediate results | Real estate transactions (preferred method) |
| Charcoal canister (professional) | $75-$150 | 48-96 hours + 3-5 days lab time | Budget option for home purchases |
| DIY charcoal test kit | $15-$40 | 48-96 hours + 5-10 days lab time | Homeowner screening (not recommended for transactions) |
| Long-term alpha track detector | $25-$50 | 90 days to 1 year | Homeowners wanting long-term average |
For a real estate transaction, expect to pay $125-$200 for a professional CRM test. Many home inspection companies in the Tampa Bay area offer radon testing as an add-on service, and some will bundle it with your general inspection for a package discount. Given the potential health implications and the relatively low cost, this is one of the most worthwhile inspection add-ons you can get.
Understanding Radon Test Results
Radon levels are measured in picocuries per liter of air (pCi/L). Here's how to interpret the numbers.
| Radon Level (pCi/L) | Risk Assessment | Recommended Action |
|---|---|---|
| Below 2.0 | Low risk | No action necessary; retest every 2-5 years |
| 2.0 to 3.9 | Moderate risk | EPA suggests considering mitigation; WHO recommends action above 2.7 |
| 4.0 and above | High risk - EPA action level | Mitigation recommended; negotiate with seller during transaction |
| 8.0 and above | Very high risk | Mitigation strongly recommended as soon as possible |
| 20.0 and above | Extreme - rare but documented in Florida | Immediate mitigation; consider temporary relocation during installation |
Context matters. The average outdoor radon level is about 0.4 pCi/L. The average indoor radon level in the U.S. is about 1.3 pCi/L. The EPA action level of 4.0 pCi/L represents a lung cancer risk roughly equivalent to smoking half a pack of cigarettes per day. That's not an alarmist comparison - it's directly from the EPA's risk assessment data.
In a real estate transaction, if the test comes back at or above 4.0 pCi/L, you have a legitimate negotiating point. You can ask the seller to install a radon mitigation system before closing, request a credit to cover the cost of mitigation, or - in cases of very high readings - consider whether you want to proceed with the purchase at all. For a deeper look at structuring your offer and negotiations, see my first-time home buyer guide for Brandon FL.
Radon Mitigation Systems and Costs
The good news about radon is that even very high levels can be reduced to safe concentrations with a properly designed mitigation system. The technology is proven, the installation is relatively straightforward, and the cost is reasonable compared to most home repairs.
How Sub-Slab Depressurization Works
The most common and effective radon mitigation method for Florida slab-on-grade homes is active sub-slab depressurization (ASD). Here's how it works in plain terms.
- A small hole (about 4-5 inches in diameter) is drilled through the concrete slab, typically in a central location or near the highest radon entry point.
- A section of the gravel or fill material beneath the slab is removed to create a suction pit.
- A PVC pipe (usually 3 or 4 inches in diameter) is inserted into the hole and routed through the home and up through the roof or exterior wall.
- A small, continuously running fan mounted on the pipe creates negative pressure beneath the slab, pulling radon gas out of the soil before it can enter the home.
- The radon is vented safely above the roofline, where it dissipates harmlessly into the outdoor air.
The system runs 24/7, uses about the same electricity as a 75-watt light bulb, and is virtually silent inside the home. A properly installed ASD system can reduce indoor radon levels by 80-99%, often bringing levels from well above 4.0 pCi/L down to below 1.0 pCi/L.
Mitigation Costs in Tampa Bay
| System Type | Typical Cost | Notes |
|---|---|---|
| Standard ASD system (1 suction point) | $800-$1,500 | Sufficient for most single-family homes |
| Multi-point ASD system | $1,500-$2,500 | Larger homes or homes with complex slab designs |
| Radon-resistant new construction | $350-$600 (added during build) | Passive system with pipe roughed in; fan added only if needed |
| Post-mitigation retest | $75-$150 | Required to confirm the system is working |
For most homes in the Tampa Bay area, a standard single-point ASD system installed by a certified radon mitigation contractor runs $800-$1,500. That's it. For a problem that causes lung cancer, the fix is surprisingly affordable. Installation takes about half a day, and the system is tested within 48 hours of installation to confirm it's working. Annual electricity cost for the fan is around $50-$75.
Radon in Well Water vs. City Water
Radon can dissolve in groundwater, and when that water is used in the home - particularly for showering, running faucets, and operating a dishwasher - the radon releases into the indoor air. This is primarily a concern for homes on private wells. If your water comes from a municipal supply (city water), the treatment and aeration process at the water plant removes most dissolved radon before it reaches your tap.
If you're buying a home on well water in the Tampa Bay area, consider testing the water for radon in addition to the standard air test. A water radon test typically costs $40-$100 and can be ordered through the same lab that handles your air test. The EPA estimates that radon in water contributes about 1-2% of total indoor radon exposure for most homes - so airborne radon from the soil is by far the bigger concern. But for homes on wells with very high water radon levels, a point-of-entry aeration treatment system ($1,500-$4,000 installed) can remove 95-99% of dissolved radon before it enters your plumbing.
Florida Radon Law and Disclosure Requirements
Florida takes radon more seriously than most states from a legal standpoint. The Florida Radon Protection Act (Section 404.056, Florida Statutes) establishes several important requirements.
- Radon disclosure in real estate transactions - Florida law requires that the following radon disclosure statement appear in all real estate contracts: "RADON GAS: Radon is a naturally occurring radioactive gas that, when it has accumulated in a building in sufficient quantities, may present health risks to persons who are exposed to it over time. Levels of radon that exceed federal and state guidelines have been found in buildings in Florida. Additional information regarding radon and radon testing may be obtained from your county health department." This is a mandatory disclosure - every buyer in Florida sees it.
- Building code requirements - The Florida Building Code requires that new construction in Zone 1 counties (including Hillsborough) incorporate radon-resistant construction techniques. This includes a gas-permeable layer (gravel) beneath the slab, a vapor barrier, sealed penetrations, and a passive radon vent pipe roughed in during construction. The passive pipe can be activated with a fan if post-construction testing reveals elevated levels.
- Contractor certification - Radon measurement and mitigation professionals in Florida must be certified by the Florida Department of Health (FDOH) or by the National Radon Proficiency Program (NRPP) or the National Radon Safety Board (NRSB). Always verify your radon tester and mitigation contractor hold current certification.
Note that the disclosure requirement is informational - it tells buyers radon exists but doesn't require sellers to test for it or disclose known radon levels. However, if a seller has previous radon test results, Florida's general property disclosure obligations may require them to share that information. If you want to know the radon level, you need to test it yourself during your inspection period.
