November 12, 2026
By Courtney Orlando, REALTOR® | Courtney Orlando Group | Compass Real Estate
A home can look clean, well-maintained, and move-in ready—and still have an indoor air quality issue that cannot be detected by sight, smell, or ordinary home inspections.
One example is radon, a naturally occurring radioactive gas that can enter a home from the soil and rock beneath its foundation. It is invisible, odorless, and tasteless. The only way to determine the radon concentration inside a home is to test it.
For New Jersey buyers and sellers, this is an important part of understanding a property's condition. Radon levels can vary significantly between neighboring homes, and a property's location, age, appearance, or previous owner's experience cannot establish whether its indoor radon level is safe.
The good news is that testing is straightforward, and elevated levels can generally be reduced through appropriate mitigation.
Here is what New Jersey homeowners and prospective buyers should know before a real estate transaction.
1. What Exactly Is Radon, and How Does It Enter a Home?
Radon is a radioactive gas produced by the natural breakdown of uranium found in soil and rock.
As it moves through the ground, it can enter a home through openings in the foundation, including:
- Cracks in concrete floors and foundation walls
- Gaps around pipes and utility penetrations
- Sump pits and floor drains
- Construction joints
- Other openings where the foundation meets the surrounding soil
Radon can accumulate indoors, particularly in lower levels of a home.
This is why basements and other ground-contact areas deserve attention during a property evaluation. However, radon is not exclusively a basement issue. Its concentration can vary throughout a building, depending on construction, ventilation, air pressure, and other conditions.
According to the U.S. Environmental Protection Agency (EPA), long-term exposure to elevated radon is a leading cause of lung cancer among nonsmokers.
It is not something a buyer can identify by walking through a property. A home may have excellent maintenance records and still require radon testing.
2. Why New Jersey Buyers Should Not Rely on a Town's Radon Rating
The NJDEP maintains a radon potential map that classifies municipalities into three categories:
- Tier 1 – High potential
- Tier 2 – Moderate potential
- Tier 3 – Low potential
These classifications are based on historical testing data from homes in each municipality.
The map is useful for understanding general radon potential, but it does not predict the result for an individual property.
Two houses on the same street can have different radon concentrations because of differences in soil conditions, foundation openings, construction, and air movement.
Even a home in a municipality classified as low potential can have an elevated radon reading.
For this reason, NJDEP recommends that homes throughout New Jersey be tested, regardless of their municipality's tier designation.
The practical lesson: Do not assume a home is free of radon because the neighborhood has historically reported lower levels. Test the actual property.
3. When Should Radon Testing Be Part of a Home Purchase?
The homebuying process is an opportunity to evaluate more than the property's visible condition.
If a home has never been tested, buyers should consider arranging a radon test as part of their due diligence. If previous testing exists, the buyer should review the report rather than relying on a verbal statement that the property was tested.
The EPA recommends testing when buying or selling a home.
Before accepting an existing report, buyers should consider:
- When was the test performed?
- Which level of the home was tested?
- Was the test conducted under appropriate conditions?
- Was the testing company qualified and certified in New Jersey?
- Were any mitigation systems installed after the test?
- Is there a post-mitigation test confirming the system's performance?
An older test may not accurately represent current conditions, particularly if the property has undergone renovations, changes to its foundation, or other alterations.
The EPA notes that a buyer may reasonably request a new test when the previous test is not recent, testing conditions were not followed, or the home's use has changed.
For example, a buyer planning to use a basement as a family room, exercise area, or bedroom should discuss the appropriate testing location with a qualified professional.
4. What Does a Radon Test Actually Measure?
Radon test results are generally reported in picocuries per liter of air, abbreviated as pCi/L.
The EPA recommends that homeowners fix a home if the radon level is 4.0 pCi/L or higher.
However, a result below 4.0 pCi/L does not mean there is absolutely no risk. The EPA recognizes that radon exposure presents some risk even at lower concentrations, and homeowners may consider reducing levels between 2.0 and 4.0 pCi/L.
Here is a simplified guide:
|
Test result |
General interpretation |
|
Below 2.0 pCi/L |
Lower measured concentration; not a guarantee of zero risk |
|
2.0–3.9 pCi/L |
Below the EPA action level; consider whether further reduction is appropriate |
|
4.0 pCi/L or higher |
EPA recommends taking corrective action |
A single result represents the conditions during the testing period. Radon levels can change with weather, seasons, ventilation, and how a home is used.
A qualified testing professional can explain the result and whether additional testing is appropriate.
5. Not All Radon Tests Work the Same Way
There are two broad categories of radon testing.
Short-term testing
Short-term tests are designed to provide results relatively quickly. Depending on the device, testing can take from two days to 90 days.
For real estate transactions, a short-term test may be useful because buyers and sellers often need information within a limited inspection period.
The EPA states that radon tests should be conducted for at least 48 hours, although individual devices may require longer.
Long-term testing
Long-term tests remain in a home for more than 90 days. They are generally more representative of the home's average radon concentration over time because they account for more day-to-day and seasonal variation.
When timing allows, long-term testing can provide a more complete picture of a property's typical radon level.
For a real estate transaction, the testing method and timing should be discussed with the testing professional so the test is appropriate for the property's circumstances and the transaction schedule.
6. Why Testing Conditions Matter During a Real Estate Transaction
A radon test is only useful when it is performed correctly.
During a real estate transaction, testing generally requires closed-house conditions. This means keeping windows and exterior doors closed except for normal entry and exit, following the applicable instructions before and throughout the test.
Opening windows to ventilate a home during testing can affect the result and may invalidate the test.
The EPA also identifies potential test interference as a concern in real estate transactions. Testing professionals may use devices or procedures that help identify whether testing conditions have changed or the equipment has been disturbed.
Buyers and sellers should avoid moving, covering, opening, or otherwise interfering with testing equipment.
In New Jersey, businesses and individuals performing radon measurement or mitigation services generally must be certified by NJDEP. Homeowners testing or mitigating their own homes are subject to a specific exemption.
For a transaction, using an appropriately New Jersey-certified professional helps ensure the test follows applicable requirements.
7. What New Jersey Sellers Should Know About Radon Disclosure
Radon testing and mitigation history can become important during a property sale.
New Jersey's radon law requires a seller to provide the buyer, at the time the contract of sale is entered into, with a copy of the results of radon testing performed on the property and evidence of any subsequent mitigation or treatment.
This makes documentation important.
Sellers should locate and organize:
- Previous radon test reports
- The date and location of each test
- The testing company's information
- Records of any radon mitigation installation
- Invoices and service records
- Post-mitigation test results
- Available system warranties or maintenance information
If a home has never been tested, sellers should not invent a result or describe the property as radon-free.
If the home has been mitigated, sellers should retain documentation showing the work performed and any follow-up testing.
Buyers should review the available information and discuss any concerns with their attorney and qualified radon professional.
8. What Happens if the Radon Result Is 4.0 pCi/L or Higher?
An elevated test result does not automatically mean a home is unsafe to purchase or that the transaction cannot proceed.
It means the result deserves attention and an appropriate response.
The most common mitigation approach is a sub-slab depressurization system. This typically uses a pipe and fan to draw radon from beneath the foundation and vent it outdoors, reducing the amount that enters the home.
Depending on the property's construction, other measures may be needed.
A qualified mitigation professional should evaluate the property and recommend an appropriate system.
After installation, follow-up testing is important to determine whether the mitigation system is working effectively.
Buyers and sellers may need to discuss:
- Whether additional testing is necessary
- The recommended mitigation method
- Who will arrange and pay for the work
- Whether mitigation should be completed before closing
- Whether post-installation testing will be required
- How the agreement should be documented
These matters should be addressed through the applicable contract terms and with guidance from the parties' real estate attorneys.
An elevated reading is a property condition to investigate—not a reason to make assumptions before understanding the available solutions.
9. What About New Construction?
A newly built home is not automatically free of radon.
New Jersey requires radon-resistant construction features in new homes built in designated Tier 1 areas under the state's radon hazard subcode.
These features can include a gas-permeable layer beneath the foundation, a plastic soil-gas barrier, sealed openings, and piping that can make a future mitigation system easier to activate.
However, passive radon-resistant features are not the same as an active mitigation system, and they do not establish that indoor radon levels are low.
For buyers considering new construction, useful questions include:
- Is the property located in a Tier 1 municipality?
- Were the required radon-resistant construction features installed?
- Is there a radon test report?
- Is the system passive or active?
- Has the home been tested after construction?
A new home should still be evaluated based on actual test results rather than assumptions about its age or construction.
10. A Practical Radon Checklist for New Jersey Buyers and Sellers
Before completing a transaction involving a property that has a basement, crawl space, or other ground-contact living area, consider these questions:
For buyers:
- Has the property ever been tested for radon?
- Can the seller provide copies of previous test results?
- Was the test conducted by a New Jersey-certified professional?
- Was the lowest level suitable for occupancy tested?
- Does the property have a mitigation system?
- If mitigation was installed, is there a post-mitigation test?
- Should a new test be included in the inspection process?
For sellers:
- Are previous radon reports available?
- Has the property ever required mitigation?
- Are installation and maintenance records organized?
- Is the mitigation system operating as intended?
- Can all required test and mitigation documents be provided to the buyer?
These questions can help both parties understand the property's radon history and determine whether additional evaluation is appropriate.
The Takeaway: A Home's Air Quality Deserves Attention, Too
When buying a home, it is easy to concentrate on the features that are immediately visible: the kitchen, flooring, bathrooms, landscaping, and finished basement.
But some important property conditions cannot be identified during a regular showing.
Radon is one of them.
New Jersey buyers should understand that a municipality's radon classification cannot predict an individual home's test result, and a seller's previous report should be reviewed rather than accepted without question.
For sellers, accurate documentation of testing and mitigation is an important part of preparing for a transaction.
A home should be evaluated for more than what you can see. Sometimes, the most important information comes from what you cannot.
If you are buying or selling a home in Central or Northern New Jersey, Courtney Orlando Group | Compass Real Estate can help you navigate the questions worth asking throughout the real estate process.
Sources and Further Reading
- New Jersey Department of Environmental Protection (NJDEP) – Radon and Real Estate
https://dep.nj.gov/rpp/radon/radon-real-estate/ - NJDEP – Radon Testing
https://dep.nj.gov/rpp/radon/radon-testing/ - NJDEP – New Jersey Radon Potential Map
https://dep.nj.gov/rpp/radon/radon_map/ - U.S. Environmental Protection Agency – Home Buyer's and Seller's Guide to Radon
https://www.epa.gov/radon/home-buyers-and-sellers-guide-radon - U.S. Environmental Protection Agency – How Often Should I Test or Retest My Home for Radon?
https://www.epa.gov/radon/how-often-should-i-testretest-my-home-radon - New Jersey Administrative Code – Radon Testing and Mitigation Regulations, N.J.A.C. 7:28-27
https://www.nj.gov/dep/rpp/RPRP_Rules/sub27.pdf
This article is for general educational purposes only and is not medical, environmental, legal, or radon-testing advice. Testing, mitigation, and transaction requirements should be discussed with NJDEP-certified radon professionals and the parties' legal representatives.