Short answer
Soil gas is the gas in the ground under and around a building: air that carries radon and other gases up from the soil. EPA names radon from soil gas as the main cause of radon problems in homes.
What soil gas means
EPA explains why it comes indoors. Air pressure inside a home is usually lower than pressure in the soil around the foundation, so the home acts like a vacuum, drawing radon in through foundation cracks and other openings.
WHO lists the openings: cracks in the floors or at floor-wall junctions, gaps around pipes or cables, small pores in hollow-block walls, cavity walls, and sumps or drains.
Where a radon system has to release soil gas
EPA sets the distances for the exhaust of a soil suction system in feet. Each row converts one to meters.
| EPA's rule for the exhaust | Feet | Meters |
|---|---|---|
| Height above the ground, at least | 10 | 3.05 |
| Distance from windows, doors or other openings, at least | 10 | 3.05 |
| Or height above those openings, at least | 2 | 0.61 |
What it means for your home
Because the house pulls on soil gas, the standard fix works on soil gas too: a fan connected to suction pipes draws the radon from below the home and releases it into the outdoor air.
Sealing cracks is a basic part of most approaches, but EPA does not recommend sealing alone: by itself it has not been shown to lower radon levels significantly or consistently.
Where to go next
- Radon mitigation cost estimator. Price the system that deals with soil gas under your type of foundation.
- How radon gets into a house. The entry points, and why air pressure does the work.