When you’re buying a home, the last thing you want is a hidden health hazard waiting behind the front door. Most buyers are concerned with big-ticket items like roof leaks, bad wiring, or foundation cracks, but one of the most important things to test for is invisible: radon.
Including radon testing during a home inspection is a simple step and inexpensive add-on that can protect your health and give you peace of mind before signing the dotted line — whether buying a home in Denver, CO or Portland, ME.
What is radon?
Radon is a naturally occurring radioactive gas created when uranium present in soil, rock, or water breaks down. It moves upward through the ground and can enter homes through cracks in the foundation, gaps around pipes, sump pumps, or through crawl spaces.
You can’t see, smell, or taste radon, but long-term exposure to higher levels can be dangerous. According to the U.S. Environmental Protection Agency (EPA), radon is the second leading cause of lung cancer in the U.S., responsible for thousands of deaths each year.
Because radon levels can vary widely from one property to the next, even between neighboring houses, each home needs to be individually tested. Weather, climate, and temperature fluctuations can also affect radon levels, even if it wasn’t a problem in the past. This makes radon testing an essential part of the home inspection process for any buyer.
What happens during a radon inspection?
During a standard home inspection, your inspector checks parts of the home like the foundation, plumbing, HVAC, and electrical, but radon testing isn’t always included automatically. Usually, you’ll need to request it as an add-on service or hire a certified radon specialist separately.
When you include radon testing in your home inspection, the inspector places a test device in the lowest livable area of the home, like a basement or first floor, to measure gas levels over a few days. To produce accurate results, “closed-house conditions” are required (like keeping windows and doors closed for at least 12 hours before and during testing).
If a radon mitigation system is already installed, the inspector can also test whether it’s properly working.
Different types of radon testing
There are a few different ways to measure indoor radon levels. DIY radon tests and professional radon inspections both track how much radon gas accumulates in the home, but the process and testing times are different.
Passive, or DIY, radon test kits
Passive radon devices can be found at most home improvement stores. They rely on natural air diffusion to collect radon particles over a period of time, usually about a week. Charcoal canisters are the most commonly used in DIY radon tests and absorb radon over several days. Once the test is complete, the device is sent to a lab for analysis.
Pros: Affordable, simple, and can be done yourself.
Cons: If instructions and conditions are not precisely followed, the readings can be inaccurate.
Active, or continuous, radon tests
Active devices are what professional radon inspectors use. Continuous radon monitors (CRMs) record radon levels in real time. They log hourly readings and environmental factors like humidity and air pressure, giving a detailed picture of radon fluctuations and helping detect tampering or ventilation changes. Once the test is completed, usually after 48 hours, a report is ready to go.
Pros: Fast, accurate, and ideal for real estate transactions.
Cons: Higher cost and must be operated by certified professionals.
For best results, a continuous radon test by a professional is recommended—and for real estate transactions, a professional test is a must.
How much does radon testing cost?
On average, buyers can expect to pay between $100 and $250 when a radon inspection is added to a home inspection package, or homeowners and sellers can expect to pay between $300–$600 if ordered as a standalone service.
Even though costs can vary, radon testing is a small price to pay in the grand scheme of home ownership. If high levels are found, you’ll know before closing, and can negotiate mitigation or repairs rather than discovering the problem later and risking long-term health issues.
How long does a home inspection radon test take?
Most home buyers opt for a short-term test during the inspection period, but long-term testing can be valuable after moving in—especially if you plan basement renovations, finish a lower level, or live in an area with a higher risk of radon exposure.
- Short-term tests: Most professional radon inspections are performed in a 48-hour, or 2-day, period. This timeframe aligns with standard inspection periods and gives quick, reliable results to help guide purchase decisions.
- Long-term tests: These tests use alpha particle tracking to monitor radon levels over time, and run anywhere from 90 days to one year. Because radon levels fluctuate with weather and home ventilation patterns, long-term tests give the most accurate average.
- Follow-up testing: If a short-term test result is close to the EPA action level (around 4.0 pCi/L), buyers or homeowners are often encouraged to conduct another test: either a second short-term test for confirmation or a long-term test for accuracy.
What home inspection radon test results mean
The EPA measures radon levels in picocuries per liter (pCi/L) of air. Anything above 4.0 pCi/L is considered a concerning amount of radon detected.
- Below 2.0 pCi/L: Low levels; no immediate action needed.
- 2.0–3.9 pCi/L: Moderate levels; consider retesting for accuracy.
- 4.0 pCi/L or higher: Action (like remediation) is recommended
If your test shows a reading above 4.0 pCi/L, the EPA suggests taking steps to lower the radon concentration before or soon after you move in. Even if levels are slightly below that threshold, many homebuyers choose to install mitigation systems proactively.
What happens if the home inspection reveals high radon levels?
Finding high radon levels doesn’t mean you should walk away from the home. In fact, radon issues are pretty common, and highly fixable, at a generally low cost. The solution is usually to install a radon mitigation system, which helps vent the gas safely outside. Most sellers are willing to cooperate since radon issues are fixable and disclosure laws require honesty about known problems.
Professional radon mitigation systems, like the pipe and fan system, typically cost $800 to $1,500, depending on the home’s size and foundation type. Once installed, they can reduce radon levels by up to 99%, and most systems are quiet, energy-efficient, and easy to maintain.
After installation, a follow-up test is performed to make sure the system is working as it should. Ongoing retesting every two years is recommended, or sooner if you renovate the basement or change the HVAC system.
Steps to reduce radon levels
- Seal foundation cracks and gaps: Use caulk or polyurethane sealant to close openings around pipes, drains, and floor joints where radon can enter.
- Improve ventilation: Increase airflow by using existing fans, adding air exchangers, or occasionally opening windows and doors to help dilute indoor radon levels.
- Treat your water if needed: In rare cases where radon might enter the home through well water, installing a water filtration or aeration system can help.
- Use radon-resistant techniques during renovations: If you’re remodeling or finishing a basement, preventively add vapor barriers, sub-slab venting, or sealed sump lids to prevent future buildup.
- Install a radon mitigation system: A licensed contractor can add a vent pipe and fan system that draws radon from beneath the foundation and releases it safely outdoors.
What houses are most at risk for radon?
While radon can be found in any home, anywhere, certain factors make some properties more vulnerable than others. Radon enters through cracks in foundations, sump pumps, crawl spaces, and gaps around pipes, so the way a home is built and maintained plays a big role in how much gas accumulates indoors.
Homes most at risk for high radon levels include:
- Homes with basements or crawl spaces: Radon seeps up from the soil, so houses with dirt foundations, open-air crawlspaces, or other exposure of the ground to the living space might have higher levels than those built on slabs.
- Older homes with foundation cracks: Settling over time can open small gaps that allow more radon to enter.
- Tightly sealed, energy-efficient homes: Ironically, well-insulated newer homes can trap radon indoors because less air circulates naturally.
- Homes in high-radon regions: The EPA notes higher-risk zones include the Midwest, Northeast, Appalachia, and the Rocky Mountain states, where uranium-rich soil releases more radon gas. But elevated radon levels have been found in every U.S. state.
- Neighboring homes with known radon issues: Radon can vary significantly from one property to the next, even on the same street—but if your neighbor has high levels, the soil might be similar on your property.
- Homes that rely on well water: Radon can seep through the groundwater, so if your home has a well, it’s important to get the well inspected and treated as necessary.
No home is completely immune to radon, and even new homes can have high readings. Builders in many areas now include radon-resistant construction techniques, like vent pipes or vapor barriers, but testing is still recommended after move-in or as part of your new construction home inspection.
Is radon testing really necessary?
The short answer is yes: radon testing during a home inspection is absolutely worth it. Because radon is colorless and odorless, the only way to know if it’s present at unsafe levels is through testing. The EPA estimates that roughly one in 15 homes in the U.S. has elevated radon levels, and they can occur in any state, regardless of a home’s age or foundation type.
Weather, climate, and temperature changes can cause changes within the soil that allow radon to form and enter the home, so even if levels were fine in the past, testing every two years is recommended.
That’s why including a radon test in your home inspection protects both your health and your home long term. If high levels are detected, you can negotiate mitigation with the seller or plan for improvements before moving in. Even if results come back low, you’re better off knowing your health is safe. For the small cost involved, a radon inspection is one of the smartest and simplest steps you can take when buying a home.
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