1. Why Split-Levels Are Different
A split-level home has floor levels that are staggered, typically with half-flights of stairs connecting them. Unlike a traditional two-story home with a single foundation level, a split-level may have two or three different foundation depths. Each of these levels has its own contact area with the soil and its own potential radon entry points.
The lowest level of a split-level often sits partially or fully below grade, similar to a basement. The mid-level may be at grade, and the upper level is above grade. This staggered arrangement creates a more complex relationship between the home and the soil beneath it compared to a simple slab-on-grade or full-basement design.
The open stairways between levels also create airflow pathways that can distribute radon throughout the home. Warm air rising through the stairwell creates a natural draft that can pull soil gas from the lower levels and distribute it to the upper levels, though concentrations are typically highest on the lowest level.
2. Multiple Foundation Levels
The most significant radon challenge in a split-level home comes from having multiple foundation sections at different depths. Each section has its own slab, its own wall-floor joints, and its own crack patterns. The joint where two foundation sections meet at different heights is particularly important because it often creates a gap that serves as a radon entry point.
The lower foundation section is closest to the deepest soil and therefore closest to the primary radon source. However, the step in the foundation where the lower and upper sections meet can also be a significant entry point. This transition area often has construction joints, filled block cores, or other features that allow soil gas to travel into the home.
Lower foundation section
Sits deepest in the soil. Has the most direct contact with radon-producing geology and is often the primary entry zone. This is typically the below-grade portion of the home.
Foundation step or transition
Where the lower and upper foundation sections connect. Construction joints and block walls at this transition can be significant radon pathways, especially if not properly sealed during original construction.
Upper foundation section
Sits at or near grade level. Has less soil contact but can still have radon entry through slab cracks and penetrations. Often has lower radon levels than the lower section but should not be ignored.
3. Airflow and Pressure Challenges
Split-level homes have naturally complex airflow patterns because of their open stairways and staggered floors. The stack effect, where warm air rises and creates negative pressure at lower levels, is amplified in a split-level because there are multiple transition points where air can move between levels.
The open stairway between the lowest and middle levels acts as a chimney. Warm air rises through this opening, pulling cooler air (and soil gas) into the lower level to replace it. This effect is strongest in winter when the temperature difference between indoor and outdoor air is greatest, but it operates year-round to some degree.
HVAC Zoning Matters
If your split-level has a single HVAC zone trying to serve multiple levels, the system may create uneven pressure across the home. Return air ducts concentrated on one level can create negative pressure there, potentially increasing radon entry. Consider whether your HVAC setup is contributing to uneven pressure between levels.
4. Where to Test in a Split-Level
The standard recommendation is to test on the lowest livable level of the home. In a split-level, this is the lowest section that is used as living space. This could be a ground-level family room, a below-grade recreation room, or whichever level sits closest to the soil.
If you are concerned about radon exposure on multiple levels, you can request tests on two levels simultaneously. This tells you whether radon is concentrated on the lowest level or whether it is being distributed to other levels through airflow patterns.
For real estate transactions, testing on the lowest livable level is the standard protocol. If the home has an unfinished lower level that could reasonably be finished in the future, some inspectors will test there as well to capture what radon levels would be in a future finished space.
5. Mitigation for Split-Level Homes
Mitigating radon in a split-level home follows the same principles as any other home, but the multiple foundation sections may require additional consideration. A sub-slab depressurization system creates negative pressure beneath the slab, drawing radon away before it enters the living space.
In a split-level, the radon professional needs to evaluate whether a single suction point can adequately depressurize all foundation sections. In some cases, the sub-slab material (gravel, sand, or compacted fill) connects well enough between sections that one suction point creates sufficient vacuum throughout. In other cases, the foundation step between levels acts as a barrier, requiring suction points on each foundation section.
A good radon professional will perform diagnostic testing during installation to verify that the system is creating adequate suction across all foundation areas. This typically involves drilling small test holes in each section and measuring the pressure field created by the fan.
Effective Results
Even though split-level homes can be more complex to mitigate, a properly designed system achieves the same excellent results as in any other home type. Most split-level homes see post-mitigation levels well below 2 pCi/L with a correctly installed system. Regular fan checks and our radon solutions for homeowners keep your system running effectively.
6. Common Split-Level Types in Georgia
Georgia has several common split-level home styles, each with its own radon considerations.
Split Foyer
You enter at the middle level and go up or down a half flight. The lower level is typically partially below grade. This style is very common in suburban Atlanta and has significant radon potential on the lower level due to its below-grade position.
Tri-Level Split
Three distinct levels staggered by half flights. The lowest level is at or below grade, the middle is at grade, and the upper is a full story up. Multiple foundation depths mean more potential entry points and more complex mitigation requirements.
Side Split
One side of the home is one story and the other is two stories, with the lower level of the two-story side at or below grade. The foundation transition runs down the middle of the house and can be a significant radon pathway.
Daylight Basement Split
Built into a slope with the lower level exposed on the downhill side. Common in north Georgia's hilly terrain. The below-grade walls are in direct contact with soil and are potential radon entry points in addition to the slab.
