The most effective way to remediate radon in a home is a system called active soil depressurization, which uses a fan and piping to pull radon gas from beneath your foundation and vent it safely outdoors. The EPA recommends fixing your home if radon levels reach 4 pCi/L or higher, and suggests considering remediation even between 2 and 4 pCi/L, since there is no known safe level of exposure.
Why Radon Levels Matter
Radon is a naturally occurring radioactive gas that seeps up through soil and into homes through cracks in foundations, gaps around pipes, and pores in concrete blocks. You can’t see or smell it. Over years of exposure, it damages lung tissue and is the second leading cause of lung cancer after smoking.
The risk is dramatically higher for smokers. Out of 1,000 smokers exposed to 4 pCi/L over a lifetime, about 62 could develop lung cancer. For never-smokers at the same level, the number drops to about 7 out of 1,000. Even at the average indoor concentration of 1.3 pCi/L, a smoker has a 20 in 1,000 chance of lung cancer from radon, compared to 2 in 1,000 for someone who has never smoked. Remediation matters most in homes with elevated levels, but it meaningfully reduces risk at any concentration above outdoor background levels.
How Active Soil Depressurization Works
Active soil depressurization (ASD) is the standard remediation method for most homes with a basement or slab-on-grade foundation. The principle is straightforward: a fan connected to piping creates negative pressure beneath your foundation, pulling radon-laden soil gas out before it can enter your living space. That gas is then vented above the roofline, where it disperses harmlessly.
A contractor drills one or more suction points through the concrete slab into the gravel or soil underneath. PVC piping runs from those suction points up through the house (often through a closet or along an exterior wall) to a fan, typically mounted in the attic or on the outside of the house. The fan runs continuously, maintaining lower air pressure beneath the slab than inside the home. This pressure difference is the key: instead of radon-rich soil gas being pushed inward through cracks, clean indoor air actually flows outward through those same openings, blocking radon entry.
Active subslab suction reduces radon levels by 50 to 99 percent in most homes. The wide range depends on soil conditions, the number of suction points needed, how well the slab is sealed, and the home’s overall air pressure dynamics. In practice, a well-designed system almost always brings levels below 4 pCi/L and often below 2.
Remediation for Crawl Spaces
Homes with dirt-floor crawl spaces use a variation called sub-membrane depressurization. Instead of drilling through a concrete slab, the contractor lays a heavy-duty plastic membrane (typically polyethylene sheeting) over the exposed earth or gravel. The membrane is sealed at the edges and around any penetrations like support columns. Ventilation piping is then installed through the membrane and connected to a fan, creating the same negative-pressure effect as a subslab system.
The membrane serves as the barrier that a concrete slab would otherwise provide. Without it, radon simply rises through the soil surface across the entire crawl space. Sealing this membrane tightly is critical to the system’s performance, because any gaps reduce the pressure differential the fan can maintain.
Passive Systems and Their Limits
Some homes, particularly new construction, include passive radon piping. These systems use the same basic layout as an active system (suction point, vertical pipe, roof exit) but rely on natural air convection and temperature differences rather than a fan to move gas upward. Passive systems reduce radon by roughly 30 to 70 percent, a notably lower range than the 50 to 99 percent achieved with a fan.
If your home has passive piping and your radon test comes back high, the fix is usually simple: a qualified contractor adds a fan to the existing pipe, converting it to an active system. This is faster and cheaper than starting from scratch, since the piping is already routed through the house.
What Installation Looks Like
Professional installation typically takes half a day to a full day. Most homeowners pay between $500 and $1,500, with a median cost around $750. Several factors push the price higher or lower. Larger homes or those with complex layouts may need multiple suction points. Homes with finished basements can require more careful routing to conceal piping. If significant cracks or gaps in the slab need sealing before the system can maintain adequate pressure, that adds time and cost.
The fan is the only moving part. It’s a small, quiet inline unit that runs 24/7 and typically draws about as much electricity as a standard light bulb. Most installations include a simple visual indicator, often a U-tube manometer (a small liquid-filled gauge mounted on the pipe), that lets you confirm at a glance that the system is creating suction.
Testing After Installation
After a mitigation system is installed and activated, you need to test your home again to confirm it’s working. Post-mitigation testing should be done no sooner than 24 hours after activation but within 30 days. This window gives the system time to stabilize the pressure field beneath your foundation while ensuring you verify results promptly.
Use the same type of test you used to detect the problem. Short-term charcoal or continuous radon monitors placed in the lowest livable area of the home for at least 48 hours will confirm whether levels have dropped below 4 pCi/L. If they haven’t, the contractor may need to add a suction point, increase fan capacity, or seal additional entry points in the foundation.
Long-Term Maintenance
Radon mitigation systems are largely maintenance-free. The fan is the only component that will eventually wear out. Most fans carry a 5-year manufacturer’s warranty but commonly last 20 years or more with proper installation. You’ll know the fan has failed if the manometer gauge shows zero pressure difference, or if you can no longer hear or feel the fan running when you check it.
Check the visual indicator on your system a few times a year to make sure suction is still active. Beyond that, retest your home’s radon levels every two to three years. Soil conditions, foundation settling, and changes to your home’s ventilation can all shift radon entry over time. Testing kits are inexpensive and widely available at hardware stores or through state radon programs. A five-minute check every couple of years protects the investment you’ve already made.
Sealing Cracks Alone Is Not Enough
It’s tempting to think that caulking visible cracks in a basement floor will solve a radon problem. Sealing entry points helps improve the performance of a depressurization system by making it easier for the fan to maintain negative pressure beneath the slab, but sealing alone is not a reliable remediation strategy. Radon finds its way through microscopic pores in concrete, gaps at cold joints where walls meet the floor, and openings around utility penetrations that are impossible to seal completely. The EPA does not recommend crack sealing as a standalone fix for elevated radon.
Think of sealing as a complement to active depressurization, not a substitute. When both are in place, the system runs more efficiently, the fan works less hard, and the pressure field extends more uniformly beneath the entire slab.