How Radon Mitigation Systems Work
If your radon test came back elevated, the good news is that fixing it is straightforward. Radon mitigation is a well-understood problem with a well-understood solution. Contractors have been installing these systems for decades. The technology works.
Here is what actually happens when a mitigation system goes in.
The core problem
Your home sits on soil that contains radon. Radon is a gas, and it moves. Because your home is typically at slightly lower air pressure than the soil beneath it, air gets pulled in from the ground through any gap it can find. Cracks in your foundation floor, joints where the floor meets the wall, gaps around pipes, sump pits. Radon hitchhikes in with that air and builds up indoors.
Sealing every crack helps, but the real fix is to change the pressure relationship between your home and the soil beneath it.
Sub-slab depressurization: the standard fix
The most common and effective mitigation method is called sub-slab depressurization, or SSD. It works on nearly every home with a poured concrete slab or basement floor.
Here is what the installation looks like. A certified contractor drills one or more holes through your foundation floor, typically 3 to 4 inches in diameter. They insert a pipe and connect it to a small fan, usually mounted in the attic, crawl space, or on an exterior wall. The fan runs continuously and creates negative pressure beneath your slab. Instead of radon seeping up through your floor, it gets pulled toward the pipe and vented outside through a pipe that exits through the roof or side of the house.
That's it. Radon that would have entered your home gets routed outside before it ever reaches your living space.
The system runs 24 hours a day. It uses roughly as much electricity as a night light. It is quiet. Most homeowners forget it is running within a week of installation.
A certified contractor will assess your foundation and determine the right number and placement of suction points for your specific home. Find one using RadonLookup's contractor directory.
What happens during installation
A typical installation takes 4 to 8 hours for a straightforward home. Here is the general sequence.
The contractor inspects your foundation and determines where to place the suction point. They drill through the slab and use a vacuum to test how air moves beneath it, confirming the location will be effective. They install the pipe, route it to the fan location, install the fan, and run the exhaust pipe to the exterior. They seal the suction hole around the pipe and check the system is creating proper negative pressure.
Before leaving, a reputable contractor will either run a post-installation radon test or leave one for you to run. Most homes see levels drop below 2 pCi/L within 24 hours of the system running. Some take a few days to fully equilibrate.
The total cost for a standard installation runs $800 to $2,000 depending on home size, foundation configuration, and local labor rates. Homes with complex foundations, multiple slabs, or significant block wall construction may be on the higher end.
Variations for different foundation types
Not every home has a poured concrete basement floor. Here is how mitigation works for other foundation types.
Crawl spaces: The standard approach is to install a ground cover, a heavy plastic sheeting barrier over the bare soil floor, and vent beneath it. The barrier seals radon in the soil and a pipe with a fan exhausts it outside. Some crawl space systems also depressurize the sub-slab area if there is one.
Block foundation walls: Concrete block walls have hollow cores that can move air and radon. A contractor may need to seal the top course of blocks and install suction points that address the wall system in addition to the floor. These installations are more complex and may cost more.
Slab-on-grade homes: Same principle as basement depressurization. A suction point through the slab, a pipe, and a fan. The pipe routing is different since there is no basement to work with, but the system functions identically.
Tell your contractor about any unusual features of your foundation before they visit, including sump pits, French drains, or additions with different slab levels. These affect system design.
The fan
The fan is the heart of the system. It runs continuously and is designed for that purpose. Most mitigation fans are rated for 10 to 20 years of continuous operation. They are not the same as a standard HVAC fan.
Your system will typically include a visual indicator, either a small U-tube manometer or an electronic monitor, that shows whether the fan is creating proper suction. Check it occasionally. If the indicator shows the system is not running, check whether the fan has power and contact your contractor if the problem persists.
Fan replacement, if ever needed, typically costs $200 to $400 including labor.
What mitigation does not do
A mitigation system reduces radon levels. It does not guarantee zero radon. There is no such thing as a radon-free home. The goal is to get levels below 4 pCi/L, and ideally below 2 pCi/L. Most properly installed systems achieve this comfortably.
Mitigation also does not fix the underlying geology. Radon will always be present in the soil beneath your home. The system just ensures it goes outside instead of inside. This is why annual testing after mitigation matters. The system needs to keep running to keep working.
If you are ready to find a certified contractor, use RadonLookup's directory to find pros in your area.
DIY mitigation: honest answer
It is technically possible to install a sub-slab depressurization system yourself. The components are available and the concept is not complicated.
Tipper's honest take
If you are handy, have done serious home improvement projects, and are willing to do careful research, it is possible. If you are not sure, hire a certified contractor. The cost is reasonable for what you get.