Radon Mitigation System: How It Works and Why It’s Important

A radon mitigation system is a permanent ventilation setup, most commonly sub-slab depressurization, that pulls radon gas from beneath a home’s foundation and vents it safely outside before it can enter living spaces. It uses a sealed pipe network and an in-line radon fan to create negative pressure under the slab. Properly installed by an NRPP- or NRSB-certified professional, it reduces indoor radon levels below the EPA’s 4.0 pCi/L action level, often to 2.0 pCi/L or lower.

What Is Radon and Why Does It Matter?

Radon is a colorless, odorless radioactive gas produced by the natural breakdown of uranium in soil and rock. It seeps into homes through foundation cracks, sump pits, and utility penetrations, then accumulates indoors.

The U.S. EPA classifies radon as a Class A human carcinogen. It is the second-leading cause of lung cancer in the United States, after smoking, and the leading cause among non-smokers. The World Health Organization reaches the same conclusion in its own radon health guidance.

Radon is measured in picocuries per liter (pCi/L). The EPA action level is 4.0 pCi/L at or above this reading, mitigation is recommended. Many public health agencies, including the WHO, advise considering action even at lower levels, since no amount of radon exposure is considered fully risk-free.

Homeowners in Whitefish Bay, West Allis, Wauwatosa, and South Milwaukee sit in a region with geology known for elevated radon readings, which is why testing and, when needed, a radon mitigation system are common recommendations from local inspectors and real estate agents.

How a Radon Mitigation System Works

Most residential systems use active sub-slab depressurization (ASD), the method endorsed by the EPA and built to ANSI/AARST standards. Here’s the sequence:

1. Suction point. A hole is cut through the basement or slab floor, typically in an inconspicuous location.
2. Vent pipe network. PVC piping runs from the suction point through the house (or along an exterior wall) to above the roofline.
3. Radon fan. An in-line fan, installed in the attic or outside the conditioned space, continuously draws air and radon gas from beneath the slab.
4. Exhaust point. The gas is released above the roofline, away from windows and doors, where it disperses harmlessly into outdoor air.
5. Sealing. Foundation cracks, sump lids, and other entry points are sealed to improve system efficiency and prevent air leakage from conditioned space.
6. U-tube manometer. A simple gauge is installed to show the system is maintaining negative pressure under the slab at all times.

This creates a pressure differential: the air beneath the slab becomes lower pressure than the air inside the home, so radon gas is continuously pulled outward instead of upward into living areas. You can read a full breakdown of the radon fan and how it functions inside a mitigation system for more technical detail.

Types of Radon Mitigation Systems

Not every home uses the same configuration. The right system depends on foundation type, crawl space design, and soil conditions.

• Sub-slab depressurization (SSD) – the most common method for homes with poured concrete basements or slab foundations.
• Drain tile depressurization – uses an existing perimeter drain tile loop as the suction pathway.
• Sump hole depressurization – seals and repurposes an existing sump pit as the suction point.
• Sub-membrane depressurization – used for crawl spaces, where a heavy plastic vapor barrier is sealed over exposed soil and connected to the fan system.
• Block wall suction – used when radon enters through hollow concrete block foundation walls.

A licensed technician determines the correct configuration after inspecting the foundation. Our guide on different types of radon mitigation systems covers each method in more depth.

Why a Radon Mitigation System Is Important

It directly reduces lung cancer risk

The EPA estimates radon contributes to roughly 21,000 lung cancer deaths annually in the U.S. Lowering indoor radon concentration below the action level measurably reduces long-term exposure risk.

It protects long-term property value

Elevated radon levels are a common finding during home inspections. An installed, working mitigation system reassures buyers and can prevent negotiation delays during a sale, a point covered in our article on whether to buy a house that already has a radon mitigation system.

It works continuously, without homeowner effort

Once installed, the system runs 24/7 with minimal maintenance. The manometer provides a visual, at-a-glance confirmation that suction is active.

It addresses a risk that testing alone cannot fix

Testing identifies the problem. Only mitigation resolves it. Homes cannot “air out” radon permanently through ventilation alone, since the gas is continuously generated from the soil.

Signs Your Home May Need a Radon Mitigation System

• A short-term or long-term radon test result at or above 4.0 pCi/L
• A newly finished basement with no prior radon testing
• Visible foundation cracks, an open sump pit, or exposed crawl space soil
• A home located in an EPA Zone 1 county, which includes much of southeastern Wisconsin
• No radon system despite the home never having been tested

If any of these apply, a certified radon measurement professional should test before deciding on mitigation.

Installation: What to Expect

A typical installation takes one day. The process includes:

1. Foundation inspection and system design
2. Drilling the suction point and routing pipe
3. Fan installation and electrical connection
4. Sealing cracks and openings
5. System startup and pressure verification
6. Post-installation radon retest (usually 24–48 hours after activation)

Homeowners in the Milwaukee area can review a step-by-step walkthrough in our guide on how a radon mitigation system is installed.

Choosing a Certified Radon Mitigation Professional

Radon mitigation should always be performed by a contractor certified through the National Radon Proficiency Program (NRPP) or the National Radon Safety Board (NRSB). Certification ensures the installer follows ANSI/AARST standards for system design, fan sizing, and sealing technique.

DIY radon reduction methods, such as increased ventilation or sealing alone, rarely achieve consistent results and are not a substitute for a properly engineered system. For a closer look at why professional installation matters, see how to hire a certified radon mitigation contractor in Milwaukee.

Maintaining Your System

A radon mitigation system requires little upkeep, but it isn’t maintenance-free:

• Check the manometer monthly to confirm the system is running.
• Retest radon levels every two years, or after any foundation work.
• Replace the radon fan when it fails or becomes noisy, typically every 5–10 years.
• Schedule a professional inspection annually, especially in older systems.

Our article on why annual radon system inspections are critical explains what a professional checks during that visit.

Frequently Asked Questions

Final Thoughts

Radon does not announce itself. It quietly accumulates and slowly increases risk over time. The good news is that it is one of the most manageable indoor air quality issues when addressed properly.

Understanding how a radon mitigation system works removes uncertainty. Knowing why it matters motivates action. Testing provides clarity. Mitigation delivers results.

For homeowners in Milwaukee and throughout Wisconsin working with experienced professionals like Milwaukee Radon Home ensures that Radon Testing and Radon Mitigation are handled correctly from start to finish.

If you are ready to take the next step or simply want expert guidance, reach out at 414-455-7279 and start the conversation. Protecting your indoor air is not complicated. It just starts with the decision to act.