Michigan's Housing Stock and Radon: Why Older Homes Need Extra Attention

Michigan has a lot of old houses. That is not an observation about the state's character — it is a demographic and economic reality that has direct implications for radon exposure across the region. The combination of Michigan's industrial history, its patterns of population growth and decline, and the pace of new residential construction relative to the existing housing base means that a substantial portion of Michigan homeowners live in homes that were built before radon was understood, before radon-resistant construction existed, and before the conversation about indoor air quality had expanded to include the gas rising from the ground beneath residential foundations.

Understanding why older homes present a heightened radon concern — and what that means practically for homeowners in them — is the focus of this post.

Michigan's Housing Age Profile

Michigan's housing stock skews older than the national average. A significant percentage of homes across the state were built before 1980 — before the EPA had established radon guidelines, before the Stanley Watras story in 1984 brought national attention to residential radon risk, and before any of the construction practices designed to resist radon entry existed as standard or even optional approaches. In cities like Grand Rapids, Detroit, Flint, Lansing, and their surrounding communities, a substantial share of the residential inventory dates to the mid-twentieth century or earlier.

This is not a problem unique to Michigan's urban centers. Rural communities across Kent, Ionia, Barry, Ottawa, Allegan, and Muskegon counties — the West Michigan region All Michigan Mitigation serves — have their own concentrations of older housing that reflect the agricultural, manufacturing, and small-town development patterns of the region's past. A farmhouse built in 1940 outside of Hastings and a mid-century bungalow in a Grand Rapids neighborhood share the same fundamental challenge: they were built by people who had no knowledge of radon and no reason to take precautions against it.

What Makes Older Homes More Vulnerable

The heightened radon concern in older homes is not simply about age as an abstract category. It is about the specific physical characteristics that older homes develop over time and the construction practices that defined how they were built in the first place.

Foundation degradation over time. Concrete is durable but not permanent. Over decades of seasonal freeze-thaw cycling — something Michigan foundations experience with particular intensity — concrete slabs and foundation walls develop cracks, gaps, and surface deterioration that create radon entry pathways. A foundation that was poured in 1955 has been through seventy winters of freeze-thaw stress by now. The cumulative effect of that stress in the form of small cracks and widened construction joints is a foundation that allows far more radon entry than the same foundation would have allowed when it was new.

Mortar joints in block foundations — common in homes built through the mid-twentieth century — deteriorate similarly. Block foundations have inherent entry vulnerability because of the hollow cores in the blocks themselves, which allow radon to migrate upward through the wall regardless of surface cracks. As the mortar between blocks ages and develops gaps, that vulnerability increases. Many older Michigan homes with block foundations have never been evaluated from a radon perspective despite presenting some of the most significant entry risk of any foundation type.

Stone foundations. Some of Michigan's oldest homes — dating to the late nineteenth and early twentieth centuries — have stone foundations rather than poured concrete or concrete block. Stone foundations are essentially incompatible with the concept of radon sealing. The gaps between stones, the mortar that has often deteriorated over a century or more, and the inherent porosity of the foundation system mean that radon entry through a stone foundation is essentially unrestricted. Homes with stone foundations are among the highest priority candidates for professional radon testing in any county.

Original construction practices. Homes built before the 1970s were generally not built with airtightness as a design goal. They were designed to breathe — intentionally or incidentally — in ways that have been progressively engineered out of more modern construction. Paradoxically, this means that some very old homes with drafty construction and significant natural air infiltration may actually dilute radon somewhat through unintentional ventilation. But the same gaps that allow some dilution also allow radon entry, and the net effect varies enormously from home to home. The only reliable way to know whether a drafty old house is better or worse off than a tighter newer home from a radon standpoint is to test both.

No radon-resistant features. Modern construction in high-risk areas can include passive radon-resistant features — a layer of aggregate beneath the slab, a plastic vapor barrier, and a passive vent pipe that can be activated into an active system if testing reveals elevated levels. None of these features exist in homes built before they were developed and adopted. An older home has no sub-slab aggregate layer designed for radon management, no vapor barrier, and no passive vent waiting to be activated. It starts from a more vulnerable position and requires active mitigation rather than simple activation of existing passive systems.

Renovations and Older Homes: A Compounded Consideration

Older Michigan homes are also more likely to have undergone multiple renovation cycles over their lifetimes — kitchen updates, bathroom additions, basement finishing, HVAC replacements, foundation repairs. As we discussed in our post on home renovation and radon, certain renovation activities can change a home's radon dynamics by creating new entry pathways or altering pressure characteristics. In an older home that has been through multiple renovation cycles, the current radon entry profile may bear little resemblance to what the original construction would have presented.

This layered history makes assumptions based on the home's original construction type particularly unreliable. A 1950s ranch that has had its basement finished, its foundation crack-injected, its HVAC system replaced twice, and a bathroom addition built on a new slab is a radon environment defined by decades of accumulated changes rather than by its original construction. Only a current professional test reflects that accumulated reality.

The Radon-Unaware Generation of Homeowners

There is a human dimension to the older housing stock issue that is worth acknowledging directly. Many of Michigan's older homes have been owned by the same families for decades — purchased in the 1960s or 1970s and passed down or held through the period when radon awareness was developing. The families in these homes may have a deep and genuine connection to the property without having ever engaged with the radon question simply because it was not part of the conversation when they moved in.

For homeowners who have lived in a pre-1980 home for twenty or thirty years without testing, the instinct to avoid testing because of what they might find — a form of motivated ignorance that is entirely human and understandable — is worth gently challenging. The health implications of decades of elevated radon exposure are not changed by continuing to avoid the knowledge. Testing provides information that can inform decisions going forward, including mitigation that reduces exposure for remaining years of occupancy and for any subsequent owners.

What Older Home Owners Should Do

If you live in a pre-1980 Michigan home — regardless of its specific age, foundation type, or how long you have lived there — a professional radon test is the single most important first step. Given the geological context of West Michigan and the physical vulnerability of older foundations, the probability of finding elevated levels is meaningfully higher than in a newer home. Finding elevated levels is not a catastrophe — it is information, and it is actionable information at that.

Mitigation works effectively in older homes. The age and construction type of the home do not prevent sub-slab depressurization from performing well. In some cases, older homes with existing aggregate beneath the slab from original construction actually provide good sub-slab communication that supports effective single-point mitigation. In others, the specific foundation characteristics require a more tailored approach. Either way the path to a safe and measured radon level is available regardless of when the home was built.

At All Michigan Mitigation, we work in older Michigan homes regularly and bring specific experience with the foundation types, construction characteristics, and radon entry profiles that define the region's older housing stock. Radon testing and mitigation is everything we do, and that focus means every home we work in — regardless of age — gets the attention its specific situation requires.

Visit us at allmichiganmitigation.com to schedule your test or reach out with any questions about what radon testing and mitigation looks like in an older Michigan home.

All Michigan Mitigation is a West Michigan radon testing and mitigation company dedicated exclusively to helping homeowners understand and eliminate radon risk in their homes.