20 Facts About Radon Gas Every New Jersey Homeowner Should Know

Radon is one of those environmental hazards that most New Jersey homeowners have heard of but few fully understand. It’s invisible, odorless, and tasteless — the only way to know it’s present is to test for it. And in a state whose geology puts a significant portion of its housing stock at elevated risk, understanding how radon works, where it comes from, and what it does inside a home is genuinely important. Whether you’re a longtime NJ homeowner who has never tested, a buyer evaluating a property, or someone who tested years ago and hasn’t thought about it since, these twenty facts will give you a clear, accurate picture of what radon is and why it matters specifically in New Jersey.

1. Radon Is a Naturally Occurring Radioactive Gas Produced by Uranium Decay

Radon forms when uranium — a heavy metal present in small amounts throughout soil, rock, and water — breaks down through a series of radioactive decay steps. Uranium decays to radium, and radium decays to radon gas. This process is continuous, ongoing wherever uranium-bearing geology exists, and it cannot be stopped or altered by any human activity. The gas is chemically inert, meaning it doesn’t bind to other elements or react with its surroundings — it simply diffuses through porous soil and rock and, when it finds a pathway, moves into the air above ground or into enclosed spaces below it.

2. Radon Is the Second Leading Cause of Lung Cancer in the United States

According to the U.S. Environmental Protection Agency, radon is responsible for approximately 21,000 lung cancer deaths each year in the United States — making it the second leading cause of lung cancer overall, behind only cigarette smoking. It is the single leading cause of lung cancer among people who have never smoked. The mechanism is well understood: when radon gas is inhaled, it decays inside the lungs and releases radioactive particles that can damage the DNA of lung cells. Long-term exposure to elevated concentrations is what converts a background risk into a meaningful one, which is why the amount of radon in your home and how long you spend there both matter.

3. Smoking and Radon Together Create a Dramatically Higher Cancer Risk

For smokers, radon exposure is far more dangerous than for non-smokers — not just slightly more dangerous, but dramatically so. The World Health Organization estimates that smokers exposed to radon are approximately 25 times more likely to develop lung cancer than non-smokers exposed to the same radon levels. The two risk factors interact synergistically, not additively. For NJ homeowners who smoke or live with a smoker, this makes radon testing and mitigation even more urgent — the combined risk profile is substantially higher than either exposure alone would suggest.

4. Radon Has No Color, No Smell, and No Taste

There is no sensory way to detect radon. It cannot be seen, smelled, or tasted at any concentration that would be found in a residential setting. This is what makes it particularly insidious — unlike mold, which is visible, or a gas leak, which has an odor, radon gives no indication of its presence regardless of how high the concentration climbs. A home with radon at 20 pCi/L feels and smells identical to a home at 1 pCi/L. Testing is the only way to know, which is why relying on a neighbor’s experience, a general sense of the area, or the absence of symptoms is not a reliable approach to evaluating radon risk.

5. New Jersey Is Classified as an EPA Zone 1 State — the Highest Risk Category

The EPA divides the United States into three radon potential zones based on predicted average indoor radon screening levels. Zone 1 — the highest risk designation — applies to areas where the predicted average indoor radon level is above 4 pCi/L. New Jersey as a whole carries a Zone 1 classification, reflecting the state’s geology and the documented testing data collected from NJ homes over decades of measurement. This doesn’t mean every home in NJ has elevated radon — it means the state’s baseline risk profile places it among those where testing is most strongly warranted and where the likelihood of finding actionable levels is highest.

6. The Reading Prong Is the Geological Root of NJ’s Elevated Radon Risk

New Jersey’s radon problem has a specific geological cause: the Reading Prong, a band of uranium-rich Precambrian granite that runs from eastern Pennsylvania through northwestern New Jersey and into southern New York State. This ancient rock formation is exceptionally rich in uranium relative to most other regional geology, which means it generates radon at elevated rates as that uranium slowly decays. The counties that sit on or near the Reading Prong — Sussex, Warren, Hunterdon, Morris, Somerset, Passaic, and portions of Mercer — consistently show the highest indoor radon readings in the state. Research published in peer-reviewed journals has confirmed that counties associated with Reading Prong granite deposits have significantly higher age-adjusted lung cancer rates than nearby control counties not underlain by this formation.

7. NJDEP Tier 1 Counties Have the Highest Documented Radon Potential in NJ

The NJDEP assigns each NJ municipality a radon potential tier based on actual testing data. Tier 1 is the highest designation — applied to municipalities where at least 25% of tested homes have exceeded the 4 pCi/L action level. Tier 1 municipalities are concentrated in Hunterdon, Mercer, Morris, Passaic, Somerset, Sussex, and Warren counties, all of which align directly with the Reading Prong and related high-uranium formations. Tier 2 municipalities have between 5% and 24% of homes exceeding the threshold. Even in Tier 3 areas — where the predicted risk is lower — the NJDEP and EPA both recommend testing, because local geology can vary significantly even within a single municipality, and a home’s foundation type, construction, and ventilation patterns all affect actual indoor levels independent of regional averages.

8. Your Neighbor’s Radon Level Tells You Nothing About Yours

This is one of the most important and most frequently misunderstood facts about residential radon. Two homes on the same street, with similar construction, built in the same year, can have dramatically different indoor radon concentrations — because the pathways through which radon enters and the specific soil conditions directly beneath each foundation vary at a very local level. A neighbor who tested at 2 pCi/L is not evidence that your home is safe. Conversely, a neighbor who tested at 8 pCi/L doesn’t guarantee your home is elevated. The only way to know your home’s radon level is to test your home specifically, placed in the lowest livable level, under closed-house conditions, for the appropriate duration.

9. Radon Enters Homes Through Any Opening in Contact with the Soil

Radon moves as a gas through porous soil and fractured rock, following pressure gradients from the ground toward lower-pressure spaces above — which in most homes means the interior. The primary entry points are wherever the building’s envelope meets or penetrates the ground: foundation cracks, floor-wall joints, gaps around pipe and utility penetrations, open sump pits, hollow concrete block walls (which are particularly effective at channeling radon), crawl space openings, and floor drains. The type of foundation matters — a full poured concrete basement, a block wall basement, a slab-on-grade, and a crawl space all have different characteristic entry patterns — but no foundation type is immune. Radon has been measured at elevated levels in homes with every foundation type found in NJ residential construction.

10. Lower Floors Always Have Higher Radon Concentrations

Because radon enters from below, concentrations are always highest at the lowest level of a home — the basement or ground floor — and decrease as you move upward through the building. A test conducted on the second or third floor of a home will not reflect the radon exposure experienced in a finished basement or first-floor living space. This is why radon testing must be conducted in the lowest livable level of the home — the lowest level that is used or could be used as living space without structural renovation. For NJ buyers who plan to use a basement as a playroom, bedroom, or home office, a test conducted only on the main living floor significantly underestimates the actual exposure they’ll experience in that space.

11. The EPA Action Level Is 4 pCi/L — But No Level of Radon Is Completely Safe

The EPA recommends taking action to reduce radon when indoor levels are at or above 4 picocuries per liter (pCi/L) of air. The EPA also recommends considering mitigation at levels between 2 and 4 pCi/L. The 4 pCi/L action level is a practical threshold based on mitigation feasibility and cost-benefit analysis — it is not a biological safety line. The EPA explicitly states that no level of radon exposure carries zero risk. The goal of mitigation is to reduce radon to the lowest achievable level, not simply to cross the threshold below 4 pCi/L. Most professionally installed mitigation systems in NJ homes achieve post-mitigation levels well below 2 pCi/L.

12. The Average Indoor Radon Level Nationally Is 1.3 pCi/L — NJ Routinely Exceeds This

The national average indoor radon concentration is approximately 1.3 pCi/L. In NJ’s Tier 1 counties, documented testing shows that a substantial proportion of homes exceed 4 pCi/L — by definition, at least 25% of tested homes in Tier 1 municipalities have exceeded the action level, and many individual properties test considerably higher. Some northern NJ homes have recorded levels in the tens or even hundreds of pCi/L, though these represent extreme outliers. The practical point is that an NJ homeowner should approach radon with the expectation that testing is warranted and that an actionable result is a real possibility — not a remote one.

13. Radon Levels Fluctuate Seasonally — Winter Readings Are Typically Higher

Indoor radon concentrations are not static. They vary with season, weather, and occupant behavior in ways that make a single short-term test an approximation rather than a definitive measurement. In winter, homes in NJ are typically sealed against the cold — windows closed, ventilation reduced — which allows radon to accumulate at higher concentrations than in summer months when air exchange with the outdoors is greater. Barometric pressure changes can cause short-term spikes. This is why long-term tests (90 days or more) are considered more representative of average annual exposure than short-term tests, and why the EPA recommends long-term testing when the goal is an accurate picture of typical exposure rather than a transaction-driven snapshot.

14. NJ Law Requires Sellers to Disclose Existing Radon Test Results

Under New Jersey law (N.J.A.C. 26:2D-73), sellers are required to provide buyers with a copy of any existing radon test results and documentation of any radon remediation performed in the home at the time of the contract of sale. This disclosure obligation applies regardless of what the results show. What the law does not require is testing — a seller who has never tested has no results to disclose, and there is no legal mandate to test before listing or selling a home in New Jersey. A buyer who assumes that the absence of a seller disclosure means a home has been tested and found acceptable is making an incorrect and potentially costly assumption. Our guide on water quality due diligence for NJ home buyers covers how to properly structure radon and water contingencies in a purchase contract.

15. Radon Testing in NJ Must Be Performed by a DEP-Certified Technician

When radon testing is conducted in connection with a real estate transaction in New Jersey, it must be performed by a technician certified by the NJDEP’s Radiation Protection Program. A general home inspector who is not independently DEP-certified may not place or retrieve radon test devices as part of an inspection. The certified tester must start and complete the test — no portion of the process can be delegated to the homeowner, real estate agent, or anyone else. This requirement exists to ensure test integrity and prevent tampering or improper placement that could produce artificially low results. When evaluating radon test results from a prior owner or seller, confirming that testing was conducted by a certified professional is a basic due diligence step.

16. Radon Can Also Enter NJ Homes Through Well Water

Soil gas is the dominant pathway for radon into NJ homes, but private well water is a second entry route that is particularly relevant in northern NJ’s uranium-bearing geology. Radon dissolves readily into groundwater as it moves through bedrock, and when that water is used inside the home — in the shower, at the kitchen sink, through the dishwasher — dissolved radon off-gasses into the indoor air. Every 10,000 pCi/L of radon in well water contributes approximately 1 pCi/L to the whole-house indoor air average. In northern NJ counties where both soil gas radon and waterborne radon are elevated, addressing only the air pathway while leaving the water untreated can prevent a home from reaching its lowest achievable radon level. Our page on radon in NJ well water covers the testing and treatment options for the water pathway specifically.

17. Sub-Slab Depressurization Is the Most Effective Mitigation Method for NJ Homes

The most common and most effective radon mitigation technique for New Jersey residential construction is sub-slab depressurization (SSD), also called active soil depressurization. A licensed contractor drills one or more suction points through the foundation slab, inserts a PVC pipe, and connects a continuously running fan that draws radon-laden soil gas from beneath the foundation and exhausts it harmlessly outside the building envelope — above the roofline, away from windows and HVAC intakes. The pressure differential created by the fan prevents soil gas from being pulled into the home. The NJDEP has noted that this method is effective in nearly every NJ case, and a properly installed system typically reduces indoor radon to levels well below 2 pCi/L. Installation costs in NJ generally range from approximately $1,200 to $1,800 for a standard single-fan system.

18. A Radon Mitigation System Requires Post-Installation Testing and Periodic Maintenance

Installing a mitigation system is not the end of the process — it’s the beginning of an ongoing management relationship. Post-installation testing, conducted after the system has been running for at least 24 hours, confirms that the system is achieving the intended reduction. The NJDEP recommends retesting every two years after mitigation to confirm continued effectiveness, since changes in the home — new construction, foundation repairs, changes in ventilation — can affect system performance. The fan itself is a mechanical component with a service life, and fan failure is not always immediately obvious without a pressure gauge or monitor on the system. A system that has been running for years without a retest may no longer be performing as it was when first installed. Our radon mitigation service includes post-installation testing and ongoing system evaluation for NJ homeowners.

19. New Homes in NJ Are Not Automatically Safe from Radon

A common misconception is that newly constructed homes — built to modern code standards with tighter building envelopes — are less susceptible to radon than older homes. The tighter the building envelope, the less air exchange with the outdoors, which can actually allow radon to accumulate at higher concentrations than in older, draftier construction. New NJ homes built with radon-resistant new construction (RRNC) features — a gas-permeable layer beneath the slab, a polyethylene sheet vapor barrier, sealed penetrations, and a passive vent pipe — have a meaningful head start in managing radon entry, but passive systems alone do not guarantee acceptable levels. The RRNC system must be tested after occupancy, and an active fan may need to be added if testing shows levels above the action level. Buyers of newly constructed NJ homes should not assume a clean bill of health without a post-occupancy test in the lowest livable level.

20. Testing Is Simple, Inexpensive, and the Only Way to Know

All of the facts above lead to one practical conclusion: test your home. Short-term radon test kits are widely available, inexpensive, and straightforward to use — a detector placed in the lowest livable level of the home for two to seven days, then mailed to a certified laboratory for analysis. Long-term tests, left in place for 90 days or more, provide a better picture of average annual exposure. For real estate transactions, a DEP-certified professional must conduct the test. For ongoing monitoring in a home you already own, either approach is appropriate, with long-term testing preferred for accuracy. In New Jersey, with its documented geology, its Tier 1 counties, and its estimated one-in-six odds of above-average radon levels, testing is not an optional precaution — it’s a basic act of due diligence for any homeowner who spends meaningful time in their home.

• Test in the lowest livable level — basement or ground floor, in a frequently used room
• Maintain closed-house conditions during testing — windows and exterior doors closed except for normal entry and exit
• For real estate transactions in NJ, use only a DEP-certified radon measurement technician
• Retest after any mitigation system is installed — and again every two years
• If your home is on a private well in northern NJ, add a water radon test to your air test
• Don’t rely on a prior owner’s test — conditions and readings change over time

Get Your NJ Home Tested and Protected

Jersey Radon is a licensed and insured radon testing and mitigation company serving residential homes throughout New Jersey. We hold NJDEP certification for both radon measurement and mitigation, and we bring the same methodical, test-first approach to every home we evaluate — whether that’s a pre-purchase inspection for a buyer navigating a Hunterdon County real estate transaction, a baseline test for a homeowner in Morris County who has never measured, or a post-mitigation confirmation for a Sussex County home where a system was recently installed. Radon is a solvable problem, and the solution starts with knowing your number.

If you haven’t tested your NJ home for radon, or if you’ve tested and found levels at or above 4 pCi/L and want to understand your mitigation options, contact us for a free estimate or call us directly at (732) 357-1988. We serve all of New Jersey and are available any time. You can also explore our radon removal service page for more detail on the systems we install and the process we follow.