Radon in Older Homes: Why Pre-1980 Houses Deserve Extra Attention

Homes built before 1980 were constructed at a time when radon was not on anyone's radar as a residential health concern. The EPA did not begin recommending residential radon testing until 1985, and radon-resistant construction standards were not developed until the late 1980s. This means older homes were built with no consideration for radon prevention.

Beyond the lack of radon awareness, older homes have had decades to develop the physical conditions that allow radon entry. Concrete cracks as it ages. Foundations settle unevenly. Construction joints separate. Mortar in block walls deteriorates. Each of these aging processes creates or enlarges pathways for radon to enter.

Older homes in Georgia face additional challenges. The state's clay soils cause ongoing foundation movement that compounds over decades. A home that has been through 40 or more cycles of wet and dry clay expansion and contraction has experienced significant stress on its foundation, which means more cracks and gaps for radon to exploit. Learn about how radon enters your home through these pathways.

A concrete foundation begins to develop hairline cracks within a few years of being poured. These cracks are a normal part of the curing and settling process. Over decades, these cracks grow wider and deeper. New cracks develop as the soil beneath the foundation shifts. If your older home has had foundation work done, see our guide on radon after foundation repair.

Several construction practices common before 1980 can increase radon risk in ways that modern building codes have addressed.

Many older homes have dirt-floor crawl spaces or partial basements with exposed soil. Exposed soil is a major radon pathway because there is no barrier between the radon-producing soil and your indoor air. Modern construction requires vapor barriers and sealed slabs to reduce this pathway.

Older homes also tend to have hollow-block foundation walls. Unlike poured concrete, hollow block walls contain air channels that run from the footing to the top of the wall. Soil gas can enter through the footing area and travel up through these channels, entering the home through gaps at the top of the wall.

Sub-slab material beneath older homes is often less uniform than in modern construction. Some older homes have little to no gravel beneath the slab, which can affect both radon entry patterns and the effectiveness of certain mitigation approaches.

A 50-year-old home has likely gone through multiple renovations, each of which may have changed the radon dynamics. HVAC systems have been replaced, bathrooms have been added, basements have been finished, and additions have been built. Each of these projects may have created new radon entry points or changed the home's pressure dynamics.

Plumbing modifications that involved cutting through the slab create openings that are often not properly sealed. HVAC replacements may have changed ductwork layouts and pressure balance. Additions connect new foundation sections to old ones, creating joints that can become radon pathways.

If you live in an older home that has had significant work done over the years, it is worth testing even if the home was tested at some point in the past. Each renovation may have changed the radon equation, and a test from 10 or 20 years ago may not reflect current conditions.

Testing an older home follows the same process as any other home. A professional continuous radon monitor is placed on the lowest livable level for 48 hours under closed-house conditions. The results tell you whether the home needs mitigation.

If the lowest level is an unfinished basement or crawl space that you do not use as living space, the test is still placed there if the area could reasonably be finished in the future. If there is no plan to use the lower level, test on the lowest level that is actually occupied.

For older homes, we particularly recommend professional testing rather than DIY kits. A professional can observe conditions in the home that may be relevant, such as visible foundation cracks, exposed soil, deteriorating mortar, or unusual construction features. These observations can be helpful if mitigation is needed later.

Radon mitigation systems work effectively in older homes. In some cases, they work even better than in newer homes because the more permeable sub-slab conditions and additional cracks allow the depressurization field to extend more easily.

For homes with dirt-floor crawl spaces, the standard approach is sub-membrane depressurization. A heavy-duty plastic membrane is sealed over the dirt floor, and a suction pipe draws radon from beneath the membrane and vents it outside. This approach both reduces radon and helps with moisture control.

For homes with concrete slabs, the standard sub-slab depressurization system is installed. In older homes with hollow-block foundation walls, the mitigator may also need to address radon traveling through the block cavities by sealing the top of the wall or installing block-wall suction.