Pennsylvania Radon Levels: What Homebuyers Need to Know
Pennsylvania has a radon problem — a significant one. The state’s underlying geology, particularly the Reading Prong formation that runs through eastern and central Pennsylvania, produces naturally occurring uranium that decays into radon gas. This colorless, odorless gas seeps through foundation cracks, sump pits, and construction joints into homes, accumulating to levels that pose real health risks. The EPA estimates that approximately 40% of Pennsylvania homes have indoor radon levels above the 4 pCi/L action level, compared to about 15% nationally. That makes Pennsylvania one of the highest-risk states in the country.
For homebuyers, this means radon testing should be standard practice in every transaction — regardless of the home’s location within the state. This guide covers what radon is, where the risk is highest, how testing works, and what sellers are legally required to disclose.
What Is Radon and Why Does It Matter?
Radon is a naturally occurring radioactive gas produced by the decay of uranium in soil and rock. It’s present everywhere on Earth but accumulates to dangerous levels indoors when it seeps into buildings from the ground below. You can’t see, smell, or taste radon — the only way to detect it is through testing.
The health risk is clear: radon is the second leading cause of lung cancer in the United States after smoking. The EPA attributes roughly 21,000 lung cancer deaths per year to radon exposure. The risk increases with concentration and duration of exposure — living in a home with 8 pCi/L radon carries roughly four times the lung cancer risk of living in a home with 2 pCi/L.
| Radon Level (pCi/L) | Equivalent Risk | EPA Recommendation |
|---|---|---|
| 1.3 | Average outdoor level | No action needed |
| 2.0 | Average indoor level (U.S.) | Consider mitigation |
| 4.0 | 5x nonsmoker lung cancer risk | Mitigate — EPA action level |
| 8.0 | 10x nonsmoker lung cancer risk | Mitigate promptly |
| 20.0 | 35x nonsmoker lung cancer risk | Mitigate immediately; limit basement use |
Pennsylvania’s Radon Risk Zones
The EPA classifies Pennsylvania counties into three radon potential zones:
| Zone | Risk Level | Counties Include |
|---|---|---|
| Zone 1 (Highest) | Predicted avg. above 4 pCi/L | Adams, Berks, Bucks, Carbon, Centre, Chester, Clinton, Columbia, Cumberland, Dauphin, Franklin, Juniata, Lancaster, Lebanon, Lehigh, Lycoming, Mifflin, Monroe, Montgomery, Montour, Northampton, Northumberland, Perry, Schuylkill, Snyder, Sullivan, Union, York |
| Zone 2 (Moderate) | Predicted avg. 2–4 pCi/L | Allegheny, Armstrong, Beaver, Bedford, Blair, Bradford, Butler, Cambria, Cameron, Clearfield, Crawford, Elk, Erie, Fayette, Forest, Greene, Huntingdon, Indiana, Jefferson, Lawrence, McKean, Mercer, Potter, Somerset, Tioga, Venango, Warren, Washington, Westmoreland |
| Zone 3 (Lowest) | Predicted avg. below 2 pCi/L | Philadelphia (city), Wayne, Pike, Susquehanna, Wyoming, Lackawanna, Luzerne |
The Reading Prong formation, which runs from New Jersey through eastern Pennsylvania and into New England, is the primary geological driver. Counties along this formation — Lehigh, Northampton, Berks, Montgomery, Bucks, and Chester — have some of the highest indoor radon concentrations measured anywhere in the world. A 1985 discovery in Boyertown, Berks County, where a nuclear plant worker set off radiation alarms because of radon exposure in his own home, first brought national attention to the issue.
Even Zone 2 and Zone 3 counties can have individual homes with high radon. The zones predict average levels, not specific property levels. Every home should be tested regardless of zone designation.
How Radon Enters Your Home
Radon enters buildings through any opening that connects to the soil:
- Foundation cracks: Even hairline cracks in concrete slabs and basement walls allow radon to seep in
- Sump pits: Open or poorly sealed sump pits are major radon entry points
- Construction joints: The joint where the basement floor meets the foundation wall is a common pathway
- Gaps around pipes and wires: Where utility lines penetrate the foundation
- Crawl spaces: Exposed soil in crawl spaces releases radon directly into the living space
- Stone foundations: Older Pennsylvania homes with rubble stone foundations have extensive pathways for radon entry
- Well water: In some areas, well water can contain dissolved radon that is released into indoor air during showering and water use
Pennsylvania’s older housing stock — particularly stone-foundation homes in the Lehigh Valley, Lancaster County, and Chester County — can have higher radon levels than newer construction with modern vapor barriers and sealed slabs. However, even newer homes can have high radon if they weren’t built with radon-resistant construction techniques.
Testing for Radon
Radon testing is simple, affordable, and the only way to know your home’s radon level. Two main approaches:
| Test Type | Duration | Cost | Best For |
|---|---|---|---|
| Short-term (charcoal canister) | 2–7 days | $15–$30 (DIY) | Initial screening |
| Short-term (continuous monitor) | 48–96 hours | $150–$300 (professional) | Real estate transactions |
| Long-term (alpha track) | 90 days–1 year | $25–$50 (mail-in) | Confirming annual average |
| Long-term (electronic monitor) | Continuous | $150–$250 (purchased) | Ongoing monitoring |
For real estate transactions, professional testing with a continuous radon monitor (CRM) is standard. The PA DEP certifies radon testers and mitigators — always use a certified professional for transaction-related testing. DIY test kits from hardware stores or the PA DEP are fine for homeowner screening but may not be accepted in a real estate transaction.
For detailed testing and mitigation instructions, see our complete radon testing guide.
Radon and Real Estate in Pennsylvania
Pennsylvania law addresses radon in real estate transactions through the seller disclosure process:
What Sellers Must Disclose
- The PA seller disclosure form asks whether radon testing has been performed on the property
- If testing was done, sellers must disclose the results — they cannot hide known radon levels
- If a mitigation system was installed, sellers must disclose its existence and any available documentation
- Sellers are not required to test before selling, but they must disclose known information
What Buyers Should Do
- Include radon testing in your inspection contingency period
- Use a PA DEP-certified radon tester for the most defensible results
- If levels exceed 4 pCi/L, negotiate for the seller to install a mitigation system (typical cost: $800–$1,500) or provide a closing credit
- Don’t walk away from a home solely because of radon — it’s fixable. Mitigation systems work and are affordable
What Mitigation Costs
| Mitigation Type | Cost | Effectiveness |
|---|---|---|
| Sub-slab depressurization (standard) | $800–$1,500 | 90–99% radon reduction |
| Sub-membrane (crawl spaces) | $1,200–$2,500 | 85–95% reduction |
| Multiple suction points (large homes) | $1,200–$2,000 | 95–99% reduction |
| Annual operating cost (fan electricity) | $50–$100/year | Continuous protection |
Factor testing and potential mitigation into your purchase budget with our closing cost calculator.
Radon-Resistant New Construction
Pennsylvania does not mandate radon-resistant new construction statewide (unlike some states), but many builders voluntarily include passive radon features:
- Gravel layer: 4 inches of clean gravel beneath the slab for gas movement
- Polyethylene sheeting: Vapor barrier over the gravel to reduce soil gas entry
- Sealed slab: Caulking of all slab penetrations and construction joints
- Vent pipe: A 3–4 inch PVC pipe from the gravel layer through the roof, ready for fan activation if needed
These features cost $350–$500 during construction — a fraction of the retrofit cost. If you’re building new in Pennsylvania, insist on radon-resistant features. If the builder doesn’t include them, it’s a red flag about their awareness of PA-specific building concerns.
Living with Radon: Ongoing Management
If you have a mitigation system, maintenance is minimal but important:
- Check the system’s manometer (pressure gauge) monthly to verify the fan is working
- Retest radon levels every 2 years ($15–$30 DIY kit) to confirm the system maintains acceptable levels
- Replace the fan when it fails (typically every 8–12 years, $200–$400)
- If you make changes to the foundation (add a sump pit, crack the slab for plumbing, etc.), retest afterward — changes can alter radon entry points
Include radon system maintenance in your home budget. Our maintenance calculator helps you plan for all recurring homeownership expenses. Use the mortgage calculator to see your complete monthly costs.
Compare With Other States
Considering other markets? Here’s how other states compare:
- Radon in Wisconsin Homes: What Buyers Must Know
- Radon in Kentucky Homes: What Buyers Must Know
- Radon in Minnesota Homes: What Buyers Must Know
Frequently Asked Questions
How bad is radon in Pennsylvania?
Pennsylvania has some of the highest indoor radon levels in the United States. Approximately 40% of homes statewide exceed the EPA’s 4 pCi/L action level. Eastern and central PA counties along the Reading Prong geological formation are the highest-risk areas, but elevated levels can occur in any part of the state. Testing every home is essential — there’s no way to predict levels without measuring.
Which Pennsylvania counties have the highest radon?
Lehigh, Northampton, Berks, Montgomery, Bucks, Chester, Lancaster, Cumberland, and Dauphin counties have among the highest average indoor radon levels in the country. These counties sit on or near the Reading Prong geological formation, which contains uranium-bearing rock. However, even “lower risk” counties like Allegheny (Pittsburgh) and Erie can have individual homes with dangerous radon levels.
Is radon a deal-breaker when buying a home?
No. High radon is easily and affordably mitigated. A professional mitigation system costs $800–$1,500 and reduces radon by 90–99% in virtually all homes. In real estate transactions, buyers typically negotiate for the seller to install mitigation or provide a credit. Use our net proceeds calculator for detailed numbers. A functioning mitigation system is viewed as a positive feature, not a negative one. Don’t walk away from an otherwise good home because of radon — fix it.
How often should I test for radon in Pennsylvania?
Test when you first buy a home, then retest every 2–5 years, or after any major foundation work. If you have a mitigation system, retest every 2 years to confirm the system is maintaining acceptable levels. Short-term DIY test kits ($15–$30) are sufficient for periodic retesting. Professional testing ($150–$300) is recommended for real estate transactions.
Does Pennsylvania require radon testing before selling a home?
No. Pennsylvania does not require sellers to test for radon before selling. However, sellers must disclose any known radon testing results and the existence of any mitigation system on the mandatory seller disclosure form. Most buyers will test during the inspection period regardless of what the seller has done. Read our seller disclosure guide for all required disclosures.
Can radon come from well water?
Yes. In some Pennsylvania areas, groundwater absorbs radon from surrounding rock. When you use water from a private well — showering, washing dishes, running taps — dissolved radon is released into indoor air. Water-borne radon is generally a smaller contributor than soil gas, but in high-risk areas, well water testing ($30–$60 for radon-in-water analysis) is worthwhile. Treatment systems (aeration or activated carbon) cost $1,000–$5,000 if levels are elevated.