Do Older Homes in Kentuckiana Have More Radon?
As a radon mitigation professional, I get this question more than almost any other:
"Does an older house have more radon than a newer house?"
The short answer is no—not necessarily.
However, there are some important differences between designing and installing a radon mitigation system in an older home versus a newer one. Those differences can affect both the cost of the system and how it needs to be designed in order to work effectively.
Addressing the Myth
The age of your house, in the Ohio Valley or anywhere in the US, has very little effect on the amount of radon that accumulates in the basement or lowest occupied level of the home. What matters most is pressure.
Whenever your heating or air conditioning system runs, your home becomes slightly depressurized. Because radon is a naturally occurring gas, it always moves from areas of higher pressure to areas of lower pressure. Your house essentially acts like a vacuum, pulling soil gases—including radon—from beneath the foundation.
The radon level inside your home is influenced by several factors, including how much radon is being produced beneath your property, the permeability of the soil, and how much negative pressure your home creates. While older homes and newer homes may be built differently, the age of the structure itself generally has very little effect on these variables.
This is why it's common to find an older home with very low radon levels sitting next door to a brand-new home with elevated levels—or vice versa. The only way to know your home's radon level is to test it.
So Why Are Older Homes Usually More Expensive to Mitigate?
Although an older house does not automatically have higher radon levels, it is generally more difficult—and therefore more expensive—to mitigate.
The biggest reason comes down to how houses were built.
Changes in Construction Practices
The Southern Indiana and Kentucky area has many slab and crawlspace homes. This is due to a number of factors - including dense clay soil and various bedrock, sloping terrain, and high water tables. All of which can contribute to a cost effective choice to build without a basement.
In many older homes, there is little or no gravel beneath the concrete slab. Instead, the slab was often poured directly on compacted soil. Compacted soil does not allow air to move easily, making it much harder to create the field of negative pressure needed for an effective radon mitigation system.
Because of this, we typically have to remove at least 10 gallons of compacted soil from beneath the slab to create a sufficiently large suction pit. Older homes also commonly require a higher-capacity radon fan to pull air through the dense soil and create a larger pressure field beneath the foundation.
Newer homes are different.
Modern construction typically includes a layer of clean gravel beneath the slab before the concrete is poured. This gravel creates thousands of open air pathways that allow air to move much more freely beneath the foundation. As a result, much less material needs to be removed to create an effective suction pit, and a lower-capacity fan is often all that's required to depressurize the area beneath the slab.
These differences are illustrated in the table below:
When Did Construction Practices Change?
The timeline is roughly as follows:
Pre-1970: Most homes were built without a gravel layer beneath the slab.
1970–2003: Installing gravel beneath the slab became an increasingly common best practice, although it was not universally required.
2003–Present: The International Residential Code (IRC) began requiring a layer of aggregate beneath basement slabs, making this standard practice in new residential construction.
As with any rule of thumb, there are exceptions. Some homes were built ahead of their time, while others may not have followed the prevailing construction practices of the day. Every home should be evaluated individually.
Designed for Kentuckiana
The age of your home is not a reliable predictor of its radon level, but it is an important factor when designing a mitigation system. An experienced installer doesn't simply install the same system on every house—they adapt the design to the construction methods used when and where the home was built.
Whether your home was built in 1955 or 2025, in West Louisville, Brandenburg, Jeffersonville, or Floyds Knobs, the goal remains the same: create a continuous field of negative pressure beneath the foundation that safely redirects radon gas above the roofline before it can enter the living space. Understanding how your home's foundation was constructed helps determine the most effective way to accomplish that goal.
If you've never tested your home for radon, don't assume you're safe because your house is new—or because it's old. Radon cannot be seen, smelled, or tasted, and neighboring homes often have very different radon levels despite being built at the same time. Testing is the only way to know whether your home needs mitigation.
A Free Tool for Kentucky/Southern Indiana
We created an interactive map so you can check to see the approximate Radon levels near your home.
David Aldridge
Environmental Division Manager