The most effective way to remediate radon in a basement is active soil depressurization, a system that uses a fan and pipe to pull radon-laden gas from beneath your foundation and vent it above your roofline before it ever enters your living space. The EPA recommends fixing your home if radon levels reach 4 pCi/L or higher, and suggests considering action even between 2 and 4 pCi/L, since there is no known safe level of radon exposure. Most homes can be brought well below 4 pCi/L with a properly installed system costing between $800 and $2,500.
How Radon Gets Into Your Basement
Radon is a radioactive gas that forms naturally as uranium in soil and rock breaks down. It seeps upward through the ground and enters your basement through any available path: cracks in the concrete slab, gaps around pipes, the joint where the floor meets the wall, pores in the concrete itself, and open sump pits. Your home acts like a mild vacuum relative to the soil beneath it, especially in winter when heated air rises and draws replacement air from below. That pressure difference pulls radon-containing soil gas steadily into your lowest level.
Active Soil Depressurization: The Standard Fix
Active soil depressurization (ASD) is the industry-standard technique for basement radon remediation, and it works through a straightforward principle. A contractor drills a hole through your basement slab, inserts a PVC suction pipe into the gravel or soil underneath, and connects that pipe to a continuously running fan. The fan draws soil gas from beneath the foundation and routes it through piping that runs up through or along the outside of your house, exhausting it above the roofline where it disperses harmlessly outdoors.
This approach works through two mechanisms. First, it creates a low-pressure zone beneath your slab. When the pressure under the foundation is lower than the pressure inside your house, air actually flows outward through cracks and openings rather than inward, blocking radon entry. Second, the suction pulls outdoor and indoor air down into the soil around the foundation, diluting the radon concentration in the soil gas itself. Most systems rely on both effects working together.
The most common variation is called sub-slab depressurization. One or more suction pipes go vertically down through the slab from inside, or horizontally through a foundation wall from the outside. How many suction points you need depends on how well air moves through the material under your slab. Homes built over a clean gravel layer often need just one pipe. Homes with tightly packed soil or complex foundation layouts may need two or three to create adequate suction across the full footprint.
Using a Sump Pit as a Suction Point
If your basement already has a sump pit, it can often serve as the suction point for your radon system, eliminating the need to core a new hole through the slab. The pit connects to the sub-slab gravel layer and provides a natural collection point for soil gas. The key requirement is sealing the sump pit with an airtight cover so the fan draws air from below the slab rather than from inside your basement. The cover needs to accommodate your sump pump’s discharge pipe and power cord while still maintaining a tight seal. Specialty radon-rated sump covers are available, and some homeowners build custom sealed lids. The system should also allow water from floor drains, dehumidifiers, or water softeners to still reach the pit without breaking the seal.
Crawl Spaces and Dirt Floors
If your basement includes a section with a dirt floor or an adjoining crawl space, sub-slab depressurization won’t work there because there’s no slab. The solution is sub-membrane depressurization. A heavy-duty plastic membrane is laid over the exposed soil and sealed at the edges to the foundation walls. Beneath the membrane, perforated pipe or a gas collection mat is installed and connected to a vertical run of solid pipe leading to a fan mounted outside the building envelope. The fan creates negative pressure under the membrane, pulling soil gas out just like a sub-slab system does under concrete.
The membrane needs to be durable enough to hold up over time. If anyone will occasionally walk on it for maintenance or building repairs, a protective layer such as rubber roofing material should be placed on top. Items should not be stored on the membrane, since the weight can damage it and reduce the vacuum underneath. In some homes, sub-membrane depressurization is combined with sub-slab depressurization in adjacent finished sections, with balancing valves on the piping to distribute suction appropriately across different zones.
Why Sealing Cracks Alone Isn’t Enough
Sealing cracks, gaps around pipes, and the floor-to-wall joint is a worthwhile step, but it rarely solves a radon problem on its own. Concrete is inherently porous, and soil gas can permeate through the slab itself even when every visible crack is filled. Sealing works best as a complement to a depressurization system. By closing the largest gaps, you help the fan maintain stronger negative pressure under the slab with less effort, which makes the whole system more effective and can allow the use of a quieter, lower-powered fan.
Ventilation as a Supplemental Strategy
A heat recovery ventilator (HRV) can help reduce radon by increasing the flow of outdoor air into your basement. The unit brings in fresh air while capturing heat (or cooling) from the outgoing air, so you’re not dumping conditioned air outside. HRVs are most effective when used to ventilate only the basement rather than the whole house. However, their radon reduction is variable and depends on the starting radon concentration and how much ventilation air the unit can deliver. For homes with moderately elevated levels, an HRV may be sufficient. For levels well above 4 pCi/L, active soil depressurization is the more reliable choice, sometimes with an HRV as a supplement.
What Installation Looks Like
A professional installation typically takes half a day to a full day. The contractor will assess your foundation type, look for existing penetrations like sump pits that could serve as suction points, and determine how many suction points are needed. The fan is usually mounted in the attic, garage, or on the exterior wall, never inside the living space, so that any small leaks in the piping on the positive-pressure side vent outdoors rather than into your home. The exhaust pipe terminates above the roofline and is positioned away from windows and other openings.
A simple manometer (a small U-shaped tube with liquid inside) is installed on the pipe to let you visually confirm the system is running. If the liquid levels are uneven, the fan is creating suction. If they’re level, the fan may have failed and needs attention. Some systems use electronic pressure monitors instead.
The EPA estimates the average installation cost at about $1,200, with most homeowners paying between $800 and $2,500 depending on foundation complexity, the number of suction points needed, and fan size.
Testing After Installation
You should retest your home’s radon levels within 30 days of installing a mitigation system. A short-term test kit (two to seven days) placed in the lowest lived-in level will tell you whether the system is performing. The goal is a reading below 4 pCi/L, and most properly installed systems bring levels down to 2 pCi/L or lower. If the post-mitigation test still shows elevated levels, the contractor may need to add another suction point, increase fan power, or seal additional entry routes. Retesting every two years after that, or after any major renovation to your foundation, confirms the system continues to work.
Choosing a Qualified Contractor
Radon mitigation is a specialized trade, and the quality of installation directly determines whether the system works. Look for contractors certified through the National Radon Proficiency Program (NRPP). A certified Radon Mitigation Specialist has completed 40 hours of training (measurement and mitigation courses), passed a proficiency exam, and maintains 12 hours of continuing education every two years. Some companies also employ Radon Mitigation Installers who work under the supervision of a certified specialist. Your state radon office can provide a list of certified professionals in your area, and many states require certification by law before a contractor can install a system.