How Does a Radon Mitigation System Work?

Radon can enter a home from soil beneath and around the structure.

Mitigation is designed to reduce the amount that accumulates indoors.

That does not mean simply finding every visible crack and sealing it.

A typical active mitigation system instead works to control the movement of soil gas by creating a pressure difference beneath the home and providing a route for that gas to move outdoors.

The appropriate approach depends on the property.

A basement home, slab-on-grade home, crawlspace home, and mixed-foundation home may not use identical system designs.

The technical term sounds more complicated than the concept.

Think of the system as five connected parts:

1. 01

   Suction Point

   Provides access to the area beneath the slab or other collection area.

2. 02

   Vent Pipe

   Carries radon-containing soil gas through the system.

3. 03

   Fan

   Maintains the pressure difference that keeps the system operating.

4. 04

   Discharge Point

   Provides the designed location where the collected soil gas is released outdoors.

5. 05

   System Indicator

   Provides information about system operation or pressure conditions.

Each component has a different job.

And there is one more step that should not be confused with any of them:

A system indicator can tell you something about system operation. It cannot tell you the home's radon level.

The suction point gives the mitigation system access to the area from which soil gas will be drawn.

For a slab or basement application, this may involve an opening through the slab into the area beneath it.

Other foundation types may use a different collection approach.

The location is part of the system design.

A provider may propose:

• one suction point; or
• multiple suction points where the property and system design require them.

More suction points are not automatically better.

The goal is to create an effective pressure field for the conditions beneath the home—not to install the largest possible number of openings.

A useful homeowner question is:

Once soil gas is drawn toward the suction point, the system needs a controlled path to carry it away.

That is the job of the vent pipe.

The pipe connects the collection area to the rest of the mitigation system and ultimately to the outdoor discharge location.

Routing depends on the property and proposed design.

The pipe may need to account for:

• foundation layout;
• available access;
• fan location;
• interior or exterior routing;
• serviceability;
• appearance; and
• the overall system configuration.

Pipe routing should therefore be considered as part of the system design—not improvised after the other components have been selected.

When reviewing a proposal, ask the provider to show you where the pipe will run.

The fan provides the active part of active soil depressurization.

Its job is to help maintain the pressure difference needed to draw soil gas toward the collection system and move it through the vent piping.

A larger fan is not automatically a better fan.

Fan selection should relate to the system design and the conditions the system needs to overcome.

Relevant design considerations may include:

• resistance within the system;
• sub-slab conditions;
• system configuration;
• number of suction areas;
• vent routing;
• fan placement; and
• service access.

Homeowners do not need to choose a fan based on a model number or power rating alone.

A more useful question is:

The vent system needs a designed location where the collected radon-containing soil gas can be released outdoors.

That is the discharge point.

Its location is part of the overall mitigation design.

The important homeowner takeaway is not to memorize a universal clearance dimension.

It is to understand that discharge placement should be intentionally designed rather than treated as an arbitrary place to end the pipe.

A mitigation proposal should make the intended discharge location clear.

If it is not obvious from the written scope, ask the provider to show you where the system will discharge outdoors.

A mitigation system commonly includes an indicator that provides information about system operation or pressure conditions.

This gives the homeowner a way to observe whether the system appears to be operating as intended.

But the indicator has an important limitation:

That means these are three separate questions:

A normal-looking system indicator is therefore not a substitute for post-mitigation testing.

Sub-slab depressurization is a common form of active soil depressurization used with slab and basement construction.

The system creates suction beneath the concrete slab.

That suction is intended to draw soil gas toward the collection point and into the vent system rather than allowing it to move into the occupied space.

An important concept is sub-slab communication.

In simple terms, the system needs to influence the area beneath the slab effectively enough for the proposed design to work as intended.

Conditions beneath a slab are not identical from one home to another.

That is one reason two homes may require different:

• suction-point locations;
• numbers of suction points;
• fan selections; or
• system layouts.

The radon test result tells you about the measured indoor concentration.

It does not, by itself, tell you exactly how the mitigation system should be designed.

Crawlspaces can require a different approach because there may not be a continuous concrete slab beneath the area.

A mitigation approach may use a membrane over exposed soil to help separate the soil-gas collection area from the space above it.

The active system can then draw soil gas from beneath that membrane and move it through the vent system.

Conceptually:

The membrane is not simply decorative covering.

It becomes part of the soil-gas control strategy.

What about mixed foundations?

Some homes contain more than one foundation type.

For example, a property might combine:

• basement areas;
• slab areas; and
• crawlspace areas.

Those conditions may require a combined mitigation approach rather than treating the entire home as though it has one uniform foundation.

The underlying principle is similar:

The physical implementation changes with the foundation.

It is easy to assume that radon mitigation means finding visible cracks and sealing them.

Sealing can be part of a mitigation strategy.

It may help support the operation of a system by reducing uncontrolled air movement through certain openings.

But sealing visible cracks is not the same thing as creating an active soil-depressurization system.

Radon can move through pathways that are not obvious from a visual inspection alone.

The purpose of an active system is to create a controlled pressure and venting strategy beneath or around the relevant foundation area.

So the useful distinction is:

The actual combination of measures should be based on the property and proposed system.

This question is best answered by separating operation from performance.

These are related, but they are not interchangeable.

A fan can be running and an indicator can appear normal without either device directly measuring the home's indoor radon concentration.

That distinction is worth understanding before installation so you know what will happen after the physical system is complete.

Installing the physical components is not the final information point.

A homeowner should understand the post-installation process as well.

1. 01

   Verify System Operation

   Confirm that the system is operating and that the homeowner understands the system indicator.

2. 02

   Complete Post-Mitigation Testing

   Measure the indoor radon concentration after installation according to the applicable testing process.

   Learn About Post-Mitigation Testing
3. 03

   Keep the Documentation

   Retain information about the installed system, test results, provider information, warranty or service terms, and other relevant project records.

4. 04

   Understand Service and Warranty Terms

   Know what the provider covers and what you should do if a system component needs attention.

5. 05

   Know What Happens if the Result Remains Elevated

   Ask this before approving the project. The proposal or provider should explain what process applies if post-mitigation testing indicates that additional evaluation or system adjustment may be needed.

No.

The underlying goal may be similar, but the system design can vary.

Important differences can include:

01

Foundation Type

Basement, slab-on-grade, crawlspace, and mixed foundations can require different approaches.

02

Sub-Slab Conditions

Conditions beneath a slab can affect how effectively suction is distributed.

03

Number of Suction Points

One system may use one point while another requires multiple collection areas.

04

Vent Routing

The property's layout affects where piping can be installed.

05

Fan Requirements

Fan selection should relate to the system design.

06

Crawlspace Conditions

Exposed soil may require membrane-based approaches.

07

Existing Radon Information

Testing establishes the measured radon concentration and provides context for the mitigation decision.

That is why a generic system diagram is useful for understanding the principle, but not for diagnosing the exact system a particular home needs.

A common radon mitigation system uses active soil depressurization.

A fan creates suction beneath the home, drawing radon-containing soil gas toward a suction point. The gas moves through vent piping and is released outdoors before it can accumulate inside the occupied space.

The exact system design depends on the property.

After installation, post-mitigation testing is used to measure the indoor radon concentration.