When you buy a home in California, radon testing probably isn’t the first thing on your mind. Between earthquakes, wildfires, and our unique disclosure requirements, radon often gets overlooked in our state. But after 20+ years helping clients navigate California real estate, I’ve learned that radon is one of those hidden issues that deserves more attention than it typically gets – even here in the Golden State.
Does Radon Really Matter in California Homes?
Let me start by addressing the elephant in the room: many Californians believe radon isn’t an issue here. I hear it all the time from clients in places like Pasadena or San Diego – “Isn’t radon just a problem in the Midwest?” The reality is more nuanced.
While it’s true that California has lower average radon levels than many states, the EPA estimates that about 1 in 15 homes nationwide has elevated radon levels – and California is no exception. What I’ve seen in my years working this market is that radon can be surprisingly localized. You might have negligible levels in one neighborhood and concerning concentrations just a few miles away.
The California Department of Public Health maintains radon data showing that certain areas – particularly parts of the Sierra foothills, some coastal communities, and sections of the Central Valley – have higher prevalence of elevated radon. Santa Barbara County, parts of Ventura County, and even some neighborhoods in Los Angeles have shown concerning levels in past surveys.
Back in 2003 when I first started in real estate, radon was barely mentioned in California transactions. Today, I’m seeing much more awareness, especially among buyers relocating from states where testing is standard.
Understanding Radon Basics for California Homeowners
Before diving into testing methods, let’s cover the essentials:
Radon is a colorless, odorless radioactive gas that forms naturally when uranium in soil, rock, and water breaks down. It can enter homes through foundation cracks, sump pumps, or other ground contact points. The EPA considers levels above 4 picocuries per liter (pCi/L) to warrant mitigation.
The health concern is significant – radon is the second leading cause of lung cancer after smoking, responsible for an estimated 21,000 deaths annually. Between you and me, I think the health risks alone make testing worthwhile, regardless of how common high levels are in your specific area.
California doesn’t require radon testing during real estate transactions (unlike states such as Illinois or Minnesota), which is why many homebuyers here never consider it. But as someone who’s helped hundreds of families find homes throughout this state, I believe knowledge is always better than uncertainty when it comes to potential health hazards.
Short-Term vs. Long-Term Radon Testing Methods
When it comes to testing your California home, you have two main approaches:
Short-Term Testing (2-7 days)
- Charcoal canisters: Inexpensive ($15-30), widely available at hardware stores
- Alpha-track detectors: Slightly more accurate but similar price range
- Digital monitors: More expensive ($100-300) but provide continuous readings
Long-Term Testing (90+ days)
- Alpha-track detectors: The most common long-term option ($25-50)
- Electret ion chamber: More precise but typically used by professionals
My wife Elena and I used both methods when we bought our current home in Pasadena eight years ago. The short-term test gave us quick results, but the long-term test revealed seasonal variations we wouldn’t have caught otherwise.
For most of my clients, I recommend starting with a short-term test. If levels are clearly low (below 2 pCi/L) or clearly elevated (above 6 pCi/L), you have your answer. For borderline results between 2-4 pCi/L, a follow-up long-term test provides a more accurate picture of your year-round exposure.
Step-by-Step Guide to Testing Your California Home for Radon
Here’s my recommended approach based on helping numerous California homeowners through this process:
- Purchase a test kit from a hardware store, online retailer, or through your county health department (some California counties offer discounted or free test kits)
- Choose the right location:
- Place the detector in the lowest livable level of your home
- Select a room you regularly use (living room, bedroom, home office)
- Position it 2-6 feet above the floor
- Keep it away from exterior walls, windows, and high humidity areas
- Avoid kitchens, bathrooms, laundry rooms, or drafty areas
- Follow closed-house conditions for short-term tests:
- Keep windows and exterior doors closed (except for normal entry/exit)
- Don’t operate fans or ventilation systems that bring in outside air
- Maintain these conditions for 12 hours before and throughout the test
- Follow the specific test instructions for the duration (typically 2-7 days for short-term tests)
- Send the test to the lab as instructed (most kits include shipping materials)
- Interpret your results using EPA guidelines:
- Below 2 pCi/L: Low risk, no action needed
- 2-4 pCi/L: Moderate risk, consider follow-up long-term testing
- Above 4 pCi/L: Action recommended, confirm with a second test
- Above 8 pCi/L: Major concern, mitigation strongly recommended
I had clients last year who purchased a beautiful mid-century home in the Hollywood Hills. Their initial test came back at 3.8 pCi/L – just under the EPA action level. Rather than dismiss it, they did a 90-day test which revealed an average of 5.2 pCi/L, prompting them to install a mitigation system. The peace of mind was well worth the investment.
Common Testing Mistakes California Homeowners Make
Over my 20+ years in this business, I’ve seen several recurring mistakes when it comes to radon testing:
Mistake #1: Testing during unusual weather conditions
Severe storms, unusually high winds, or extreme temperature fluctuations can affect results. Aim for typical weather conditions for your area.
Mistake #2: Improper test placement
I once had clients in Sacramento who placed their test kit near an open window – a guaranteed way to get artificially low readings.
Mistake #3: Conducting just one short-term test
Radon levels fluctuate daily and seasonally. A single short-term test might not represent your true exposure.
Mistake #4: Testing only in the basement
Many California homes don’t have basements, but people often mistakenly believe only below-grade spaces need testing. In reality, you should test the lowest livable level you regularly use.
Mistake #5: DIY testing during a real estate transaction
If you’re testing as part of a home purchase, consider hiring a certified radon professional. Their results will carry more weight if negotiations become necessary.
Professional Testing vs. DIY in the California Market
While DIY test kits are perfectly adequate for most homeowners, there are situations where professional testing makes more sense:
Consider professional testing if:
- You’re in a real estate transaction with tight timelines
- Your home has an unusual design or ventilation system
- You’ve had inconsistent results from DIY tests
- You’re in an area known for higher radon concentrations
- You need the most accurate assessment possible
Professional testing in California typically costs $150-300, depending on your location and the company’s testing protocol. In high-demand markets like San Francisco or Los Angeles, expect to pay toward the higher end of that range.
I personally think DIY testing is fine for most homeowners doing routine checks, but I recommend professional testing during real estate transactions. When I helped my brother buy his home in Ventura last year, we hired a professional tester because the home was in an area with some known radon issues.
Regional Radon Variations Across California
One of the fascinating things about radon in California is how dramatically it can vary by region:
Sierra Nevada Foothills: Some of the highest concentrations in the state, particularly in El Dorado, Nevada, and Tuolumne counties.
Central Valley: Generally lower levels, though certain pockets in Sacramento and San Joaquin counties have shown elevated readings.
Coastal Regions: Typically lower than inland areas, though parts of Santa Barbara and Ventura counties have surprising hotspots.
Southern California: Generally lower risk, though I’ve seen elevated readings in specific neighborhoods in Los Angeles and San Bernardino counties.
Bay Area: Mostly low to moderate, with some exceptions in the East Bay and parts of Marin County.
What I’ve seen in my years working this market is that you can’t reliably predict radon levels based solely on region. I’ve had clients with high readings in supposedly “low-risk” areas and vice versa. This unpredictability is precisely why testing is so valuable.
What to Do If Your California Home Has High Radon Levels
If your test reveals elevated radon levels (above 4 pCi/L), don’t panic. Here’s what I recommend:
- Confirm with a second test – preferably a different type than your first test
- Consult with a certified radon mitigation contractor – California doesn’t have state certification, so look for professionals certified by the National Radon Proficiency Program (NRPP) or the National Radon Safety Board (NRSB)
- Understand the typical mitigation approaches:
- Sub-slab depressurization (most common)
- Sealing foundation cracks and openings
- Installing ventilation systems
- Sump pit covers and ventilation
- Get multiple estimates – mitigation systems in California typically cost 2,500, though complex homes can run higher
- Retest after mitigation to confirm effectiveness
I worked with a family in Monrovia a few years back whose 1920s Craftsman tested at 6.8 pCi/L. They installed a mitigation system for about $1,800, and subsequent testing showed levels below 1.0 pCi/L. The process was far less disruptive than they expected.
My Personal Advice After Decades in California Real Estate
After helping countless clients through radon testing and mitigation since 2003, here’s what I tell everyone about approaching this issue in California:
First, don’t assume radon isn’t an issue just because you’re in California. Our unique geology creates surprising variations even within the same city.
Second, if you’re buying a home, consider making radon testing part of your inspection process. It’s relatively inexpensive insurance against a significant health risk.
Third, if you test and find elevated levels, view mitigation as an investment in both health and resale value. More California buyers are becoming radon-aware, and having a mitigation system already installed can be a selling point.
Fourth, consider seasonal testing if you’re near the EPA action level. I’ve seen homes that test at 3.5 pCi/L in summer jump to 5.0+ pCi/L in winter when homes are more tightly sealed.
Finally, remember that no radon level is completely “safe” – the EPA’s 4 pCi/L action level is a guideline, not a health threshold. Even levels between 2-4 pCi/L carry some risk, so personal comfort with risk should guide your decisions.
Testing for radon in your California home is one of those precautions that’s easy to overlook but potentially significant for your family’s health. As I often tell my clients from San Diego to Sacramento – for the price of a nice dinner out, you can either confirm your home is safe or identify a problem you can fix. Either outcome is valuable.
