New Homes vs. Old Homes: Does Age Affect Radon Levels?
Updated: Jun 9
A Common Misconception About Radon Risk
Many people assume that newer homes are safer from radon than older homes—or that older homes automatically have higher risk.
In reality, the age of a home tells you absolutely nothing about its radon levels.
Radon doesn’t care when your house was built. It is entirely determined by what lies beneath your floorboards, how the building interacts with the soil, and how air moves through the foundation. A brand-new construction home can test dangerously high, while a 100-year-old historic home down the street can test completely safe.
Why Philadelphia Homes Have a Unique Radon Profile
The Philadelphia region sits on a unique geological transition zone. The ground beneath our feet is a mix of complex rock formations, ancient shales, and heavy structural soil deposits that can change drastically from one neighborhood to the next.
Because radon gas is formed by the natural breakdown of uranium in deep soil and bedrock, your true risk depends completely on your specific plot of land. In fact, Pennsylvania state testing data shows that even in the Philadelphia area, over 40% of tested homes can exceed safe radon limits.
Because the underlying geology changes so quickly, two homes on the exact same block can have completely different radon levels. There is no such thing as a "safe neighborhood" or a "safe home age."
Why New Homes Are Not Automatically Safer
Modern homes are built beautifully straight, tight, and highly energy-efficient. While these tight building standards are amazing for your monthly energy bills, they introduce a hidden side effect: they trap indoor air.
Older homes naturally breathe through microscopic gaps, but a tightly sealed modern home acts like a structural vacuum. If radon gas enters through the foundation, it has nowhere to escape and quickly accumulates to high levels inside your living zones.
Common entry paths exist in even the newest builds:
Foundation slab seams and expansion joints
Utility line penetrations (where pipes enter the floor)
Sump pump basins
Micro-cracks that form naturally as a new foundation settles
Why Older Homes Are Not Automatically Safer Either
On the flip side, older homes—like our classic Philadelphia area stone-foundation properties and brick row homes—tend to have a lot of natural air leakage. This draftiness can sometimes help dilute radon gas naturally.
However, older homes come with their own distinct foundation vulnerabilities:
Unsealed structural cracks from decades of settling
Exposed dirt floors or partially finished crawlspaces
Porous stone or brick basement walls that easily let soil gas pass through
The bottom line is that older homes aren't automatically better or worse; they are just different in how they breathe.
The Real Factor: What is Under Your Floor?
Predicting radon using the age of a house is pure guesswork. True radon risk is driven by three things:
Local Geology: The specific rock and soil composition under your property.
Foundation Integrity: How well your slab, basement, or crawlspace isolates you from the ground.
Air Pressure: How strongly your home's heating, cooling, and ventilation pull air upward out of the earth.
The Only Way to Know is to Test
Radon is completely invisible, odorless, and tasteless. You cannot see it, and you cannot guess it based on the year your home was built.
Whether you just moved into a beautiful new construction build, settled into a historic family property, or just wrapped up a major home renovation, assumptions will not protect your family's health.
In our region, radon risk is written in the ground beneath the home—not in the year the house was built. Stop guessing and get the facts with a proper, independent test.
About the Author
Moises Serrano is the owner of Liberty Radon Diagnostics LLC, an independent radon measurement company serving Philadelphia and surrounding communities. Liberty Radon Diagnostics performs radon testing and diagnostics only and does not install mitigation systems, allowing for unbiased measurement results.
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