What are average radon levels in Marietta, Georgia?

Average radon levels in Marietta range from 3.0 to 4.5 pCi/L depending on location. East Cobb areas tend to test slightly higher due to granite bedrock. Roughly 20-30% of homes tested in the Marietta area exceed the EPA action level of 4 pCi/L.

Is radon common in Cobb County homes?

Yes. Cobb County is classified as EPA Zone 2, meaning predicted indoor radon averages fall between 2 and 4 pCi/L. Many homes exceed that average. The underlying Piedmont geology produces radon throughout the county, and homes with basements or crawl spaces are especially prone to elevated levels.

How much does radon testing cost in Marietta?

Professional radon testing in Marietta typically costs $125 to $250 for a 48-hour continuous radon monitor test. DIY charcoal test kits are available for $15 to $40 plus lab fees. For real estate transactions, professional CRM testing is the standard because it provides hour-by-hour data.

Does Marietta require radon testing when selling a home?

No. Neither the City of Marietta nor the state of Georgia requires radon testing for real estate transactions. However, most home inspectors recommend it, and buyers increasingly request radon testing during the inspection period. Testing is voluntary but strongly recommended.

Radon in Marietta, Georgia: What Homeowners Need to Know

1. Why Marietta Has a Radon Problem

Marietta sits in the heart of Cobb County on the Piedmont geological province. This region is defined by ancient metamorphic and igneous rock, including granite that contains trace amounts of uranium. As uranium decays, it produces radium, which then breaks down into radon gas. That gas rises through soil and enters homes through cracks in foundations, gaps around plumbing, and other small openings.

Cobb County is classified as EPA Zone 2, which means predicted average indoor radon levels fall between 2 and 4 pCi/L. But averages can be misleading. Testing data from the Marietta area shows that a significant percentage of homes exceed the EPA action level of 4 pCi/L, and some test well above that threshold.

The city has a diverse housing stock that spans from pre-war bungalows near Marietta Square to modern subdivisions along the outskirts. Every foundation type is present: basements, crawl spaces, and slabs. Each one can allow radon entry. The only way to know your home's radon level is to test for it.

2. Neighborhood Radon Risk Areas

Radon levels vary across Marietta based on local geology, soil conditions, and home construction. While every home needs individual testing, certain areas tend to show higher readings:

East Cobb. One of the most populated areas near Marietta. Many homes here were built in the 1970s-1990s with full basements, which increases radon exposure potential. The granite bedrock in this area is closer to the surface, and testing data consistently shows elevated readings.

West Cobb. Newer subdivisions dominate this area, but new construction does not mean low radon. The geology still produces radon gas, and homes with basements or walk-out lower levels are common. Many West Cobb homes test in the 3-5 pCi/L range.

Marietta Square area. Historic homes near downtown Marietta often have older foundations with more cracks and openings. Crawl spaces are common, and many of these homes lack modern vapor barriers. The combination of older construction and local geology creates real radon risk.

Kennesaw Mountain area. Homes near Kennesaw Mountain sit on geology that produces moderate to high radon. The hilly terrain means many homes have partially below-grade spaces that are more vulnerable to radon entry.

Use our radon risk lookup tool to check the risk level for your specific Marietta zip code.

3. Foundation Types and Radon Entry

Marietta has a wide variety of home foundations, and each one interacts with radon differently:

Basements. Common in East Cobb and the Kennesaw Mountain foothills. Basements have the most soil contact and the highest potential for radon accumulation. Basement radon levels are typically higher than other parts of the home because radon enters through floor cracks, wall-floor joints, and utility penetrations.

Crawl spaces. Found in many older Marietta homes and some newer construction. Open crawl spaces allow radon to accumulate beneath the home and seep through floor gaps and ductwork. Encapsulated crawl spaces with sealed vapor barriers perform better but are not immune.

Slab-on-grade. Common in ranch-style homes and newer construction. While slabs have less soil contact area than basements, radon still enters through the natural cracks that develop in concrete over time. Plumbing penetrations and expansion joints are also entry points.

No Foundation Type Is Radon-Proof

Regardless of whether your Marietta home has a basement, crawl space, or slab, radon can still reach indoor air. Foundation type affects the most effective mitigation approach, but testing is necessary for every home type.

4. Testing Your Marietta Home

Testing for radon is simple and affordable. Here is the recommended approach for Marietta homeowners:

Choose Your Test Type

A short-term test (48 hours minimum) works for initial screening. Professional continuous radon monitor (CRM) testing is the standard for real estate transactions. DIY kits cost $15-40 plus lab fees for general screening.

Place the Test Correctly

Test in the lowest livable area. For homes with basements, test in the basement. For slab homes, test on the main floor. Keep the device away from windows, drafts, and exterior walls. Maintain closed-house conditions during the test period.

Understand Your Results

Below 2 pCi/L: Low risk, retest every 2 years. Between 2-4 pCi/L: Consider a follow-up long-term test. Above 4 pCi/L: The EPA recommends mitigation. Above 8 pCi/L: Prioritize mitigation promptly.

Seasonal variation affects results. Homes tested in winter months typically show levels 40-60% higher than summer tests. If you got a borderline result in summer, consider retesting in winter.

5. Radon Mitigation Options

If your Marietta home tests above 4 pCi/L, mitigation is effective and straightforward. The right approach depends on your foundation type:

Slab or Basement

$1,200-$2,500

Sub-slab depressurization: a suction point drilled through the slab, connected to PVC pipe and a fan that vents radon above the roofline.

Crawl Space

$2,500-$5,000

Sub-membrane depressurization: a sealed vapor barrier covers the soil with active suction pulling radon from beneath the barrier.

Both systems reduce radon by 90-99% and are typically installed in a single day. Use our mitigation cost estimator to get a more specific estimate for your Marietta home.

Marietta Homeowners

If you live in Marietta and have never tested for radon, now is the time. With 20-30% of area homes testing above the action level, there is a real chance your home is affected. Testing takes 48 hours, and if mitigation is needed, it is a one-day installation.

Radon in Marietta, Georgia: What Homeowners Need to Know

1. Why Marietta Has a Radon Problem

2. Neighborhood Radon Risk Areas