Radon in Pennsylvania Homes: Why the Risk Is Real and What Testing Actually Tells You

If you're buying or owning a home in the Philadelphia suburbs, radon deserves your attention. Not panic — attention. Here's why, and what you can actually do about it.

What Is Radon?

Radon is a naturally occurring radioactive gas produced by the decay of uranium in soil and rock. It's colorless, odorless, and tasteless — completely undetectable without testing. It seeps upward through the soil and enters buildings through cracks in foundations, gaps around pipes, and through porous concrete block walls.

Once inside, it accumulates — especially in below-grade spaces like basements and crawlspaces. And it's dangerous: radon is the second-leading cause of lung cancer in the United States, responsible for approximately 21,000 deaths per year according to the EPA. The only people at higher lung cancer risk from environmental exposure are smokers — and the combination of smoking and radon exposure is particularly deadly.

Pennsylvania's Specific Radon Risk

Pennsylvania isn't just a moderate-radon state. It's one of the highest-risk states in the country. The geology of southeastern Pennsylvania — including Montgomery, Bucks, Chester, and Delaware Counties — includes uranium-rich shales and granites that produce elevated radon at higher rates than most of the country.

The EPA's action level for radon is 4 picocuries per liter (pCi/L). Pennsylvania's average indoor radon level is approximately 6.0 pCi/L — already above the EPA action level, and significantly higher than the national average of 1.3 pCi/L. Some Montgomery County neighborhoods show average levels well above 10 pCi/L.

How does radon testing work in a Pennsylvania home?

Radon testing is simple and unobtrusive. For most home inspection situations, I use an electronic continuous radon monitor (CRM) — a device placed in the lowest livable level of the home (typically the basement) for a minimum of 48 hours under "closed house conditions."

Closed house conditions mean windows and doors remain closed except for normal entry and exit — this prevents exterior air from artificially diluting the reading and ensures an accurate measurement of the home's actual radon concentration.

At the end of the test period, the monitor produces an average reading in pCi/L, along with an hourly log that shows fluctuations over the testing period. I provide results and interpretation promptly so you can make decisions within your real estate contract timeline.

What do radon test numbers mean — and when should you mitigate?

Here's how to interpret radon test results:

Below 2.0 pCi/L: Low. No action required. Continue periodic testing as recommended (every 2 years, or any time you make major renovations that affect the foundation).

2.0 – 4.0 pCi/L: Moderate. The EPA recommends considering mitigation. Mitigation at this level is optional but beneficial, especially for long-term residents.

Above 4.0 pCi/L: The EPA recommends mitigation. At this level, you should install a radon mitigation system — and it should be a non-negotiable item in any real estate transaction.

Above 10.0 pCi/L: Mitigation should be treated as urgent. This level represents significant long-term health risk and should be addressed before extended occupancy.

What does radon mitigation involve and how much does it cost in Pennsylvania?

The good news: radon mitigation is effective and not particularly expensive. The standard system — called sub-slab depressurization — involves a licensed contractor drilling one or more holes through the basement slab, installing a PVC pipe, and running it to the exterior where a fan creates negative pressure beneath the slab, drawing radon out before it can enter the living space.

A typical installation costs $800–$1,500 for most homes. The system runs continuously (the fan uses roughly as much electricity as a light bulb) and reduces radon levels in most homes by 80–99%. Post-mitigation testing confirms the system is working.

In real estate transactions, radon remediation is frequently negotiated as a seller concession when elevated levels are found — it's a known, fixable problem with a defined cost, not the open-ended liability that first-time buyers sometimes fear.

Should You Test Even If You've Lived Here for Years?

Yes. Radon levels in a home can change over time as soil settlement creates new entry pathways, as HVAC systems change pressure relationships with the foundation, or as renovations alter the building envelope. The EPA recommends testing every two years in a home with a history of borderline readings, and after any major renovation affecting the foundation or basement.

I offer radon testing as a standalone service for existing homeowners — not just as an add-on to home inspections. If you've never tested your Montgomery County home, or if it's been more than two years, it's worth knowing. Call me at 610-348-6728.