How Radon Mitigation Works: A Homeowner's Guide

What is Radon Mitigation and how does it work?

Radon mitigation is a system that pulls radon gas from under your home's foundation and vents it safely above the roofline, where it dilutes in outdoor air. The most common setup is active soil depressurization: a fan creates suction in the soil beneath the slab, and a pipe routes the gas out.

Radon is a radioactive gas that comes from uranium breaking down in the ground. It seeps through cracks in the foundation, gaps around pipes, and even through hollow-block walls. Once inside, it can build up to levels that increase lung cancer risk over years of exposure.

The EPA and the U.S. Surgeon General recommend fixing any home that tests at or above 4.0 pCi/L (Alabama Department of Public Health). That's the action threshold. If your test comes back at 4.0 or higher, mitigation brings it down to levels comparable to outdoor air, which averages about 0.4 pCi/L nationally.

Madison County is one of the 15 Alabama counties the state names as having the highest radon potential. That means the odds of hitting that 4.0 threshold are higher here than in south Alabama. It's not a maybe for Huntsville homeowners; it's a risk that shows up on tests year after year.

How Radon Mitigation works, start to finish

A standard active soil depressurization system works by creating negative pressure under the slab. A fan mounted in the attic or outside pulls air from the soil through a suction point, and a PVC pipe carries that air above the roof.

Our crew starts by locating the best spot for the suction point. That's usually a section of the basement slab or crawlspace where the soil is most accessible. We cut a hole about four to six inches across, dig out a small pit, and seal a pipe into the opening. The pit gives the fan room to pull air from the surrounding soil rather than just the spot directly under the hole.

The pipe runs from that suction point up the side of the house to the roofline. We route it along an exterior wall or through an interior chase if there's one available. The fan sits either in the attic or mounted on the outside wall near the top of the run. It runs continuously, 24 hours a day, 365 days a year.

Every joint in the pipe is sealed, and the suction pit is covered with a vapor barrier and caulked tight. That seal is what makes the system work: if air can leak in from the basement instead of being pulled from the soil, the fan is drawing indoor air, not radon-laden soil gas. We also seal any obvious cracks in the basement floor or slab gaps around utility penetrations.

A manometer is installed on the pipe to show the system is working. It's a simple U-shaped tube with colored liquid. As long as the liquid stays at different levels on each side, the fan is running and pulling suction. If the levels equalize, something is wrong. We check that during every service visit.

The whole install usually takes a day. For a straightforward slab-on-grade or basement home, our crew is in and out in six to eight hours. Crawlspace homes take a bit longer because we have to lay a vapor barrier over the dirt floor and seal the perimeter before we can pull suction effectively.

1. Cut the suction hole.A four- to six-inch hole is cut through the slab, and a small pit is dug underneath to give the fan room to pull.
2. Run the pipe.PVC pipe runs from the suction point up the side of the house to above the roofline, with sealed joints throughout.
3. Install the fan.The radon fan is mounted in the attic or on the exterior wall near the top of the pipe run.
4. Seal and test.The suction pit is sealed, cracks are filled, and a manometer is installed to verify the system is pulling.

Why Radon Mitigation matters for your home

Radon is the second leading cause of lung cancer in the United States, after smoking. For Huntsville homeowners, the risk is higher because Madison County sits on geology that produces more radon than most of the state.

Indoor radon averages about 1.3 pCi/L nationally and outdoor air about 0.4 pCi/L (Alabama Department of Public Health). An indoor reading several times higher is the signal to act. In Madison County, readings of 8.0, 12.0, even 20.0 pCi/L are not unusual. That's five to fifteen times the action level.

The state of Alabama lists Madison County as one of the 15 counties with the highest radon potential, alongside Colbert, Franklin, Jackson, Lauderdale, Lawrence, Limestone, and Morgan across north Alabama. That's not a coincidence: the limestone and shale bedrock under north Alabama releases more radon than the coastal plain further south.

Mitigation brings those numbers down to near-outdoor levels. A properly installed system will drop a 12.0 pCi/L reading to 0.5 or lower. That's not just a number on a test; it's a reduction in the cumulative radiation dose you and your family breathe every day. The EPA estimates that radon causes about 21,000 lung cancer deaths per year in the U.S.

The cost to install a system is a one-time expense. A standard active soil depressurization system runs about $800 to $1,500 installed nationally, with complex homes reaching $2,500 or more (Angi, HomeGuide, Forbes Home, 2026). For a Huntsville home, the cost often lands toward the upper end of that range because of the clay soil common here, which requires a stronger fan and more suction points.

Compare that to the cost of a single lung cancer treatment. The National Cancer Institute puts the average cost of lung cancer treatment at over $100,000. Mitigation is cheap insurance.

A 12.0 pCi/L reading drops to 0.5 or lower after mitigation. That's a measurable reduction in daily radiation exposure.

Common problems and what causes them

Most radon problems in Huntsville homes come from three things: slab cracks, unsealed crawlspaces, and poor ventilation under the foundation. Fixing the system itself is usually straightforward; the hard part is finding all the entry points.

Slab cracks are the most common entry point. Settling foundations in the clay soil around Huntsville create hairline cracks that let radon seep in. Even a crack you can barely see with the naked eye can let in enough gas to push a test over 4.0 pCi/L. We seal those cracks during installation, but if the slab is badly cracked, we might need to install multiple suction points to cover the whole area.

Crawlspace homes are a different challenge. A dirt floor in a crawlspace is a direct pathway for radon. The standard fix is to lay a heavy-duty vapor barrier over the entire dirt floor, seal it to the foundation walls, and then pull suction from under the barrier. If the crawlspace has vents that are left open, outdoor air can dilute the radon, but it also makes the fan work harder. We seal the vents to keep the negative pressure stable.

Block foundation walls are another common issue in older Huntsville homes. Hollow concrete blocks act like a network of pipes, channeling radon from the soil up into the wall cavities. Mitigation for block walls often requires sealing the top row of blocks and pulling suction from the wall itself, not just the slab.

The biggest mistake we see is homeowners trying to fix a radon problem with sealing alone. Caulking cracks and painting the basement floor will lower radon levels a little, but not enough to bring a 4.0 reading down to safe levels. Sealing is part of the solution, not the whole solution. The fan is what does the heavy lifting.

Another mistake is assuming a new home doesn't need testing. New construction in Huntsville often includes passive radon piping (a pipe from the slab to the roof with no fan), but that system does nothing on its own. Without a fan, the pipe provides a path of least resistance, but it doesn't actively pull radon out. You still need to test, and you still need to add a fan if levels are high.

Common questions about Radon Mitigation

Frequently Asked Questions