Types of Radon Mitigation Systems: SSD, SMD, and More

Not all radon mitigation systems are the same. The right approach depends on your home’s foundation type, construction details, and the severity of the radon problem. Here’s a breakdown of the most common systems and when each one makes sense.

Sub-Slab Depressurization (SSD)

SSD is the most widely installed radon mitigation method and works in homes with basement or slab-on-grade foundations. A hole is drilled through the concrete slab, and a PVC pipe is inserted into the aggregate or soil below. An inline fan draws radon-laden air from beneath the slab and exhausts it above the roofline, where it disperses harmlessly.

SSD works by creating a slight negative pressure under the foundation, preventing radon from entering through cracks and openings. It’s effective, reliable, and typically the most affordable option. Most homes need just one suction point, though larger or compartmentalized foundations may require two or more.

Sub-Membrane Depressurization (SMD)

SMD is the standard approach for homes with dirt-floor crawl spaces. A durable polyethylene vapor barrier is laid over the exposed soil and sealed to the foundation walls. A suction pipe and fan system then draws radon from beneath the membrane and vents it outside.

The vapor barrier also reduces moisture and improves crawl space air quality, making SMD a dual-purpose upgrade. Proper sealing at all edges, piers, and penetrations is critical — gaps in the membrane will reduce the system’s effectiveness.

Drain Tile Suction

If your home has an existing perimeter drain tile system (interior or exterior), a mitigation contractor can sometimes tap into it as a suction point. This approach avoids drilling through the slab and can provide excellent coverage since drain tiles run along the entire foundation perimeter. Not all drain tile systems are suitable — the tiles need to be connected and have adequate airflow for this method to work.

For cost information, see our radon mitigation cost guide.

Which System Is Right for Your Home?

The foundation type is the primary deciding factor. Basements and slabs get SSD. Crawl spaces get SMD. Homes with both (a common setup) may need a combination. An experienced radon mitigator will run a diagnostic pressure test to determine how many suction points are needed and where to place them for maximum coverage.

If you’re building new, the same system can be roughed in during construction at roughly a third of the retrofit cost. See our guide on radon mitigation in new construction (RRNC) for what to ask your builder.

Regardless of system type, a properly installed mitigation system should reduce radon levels by 80% to 99%. Post-installation testing confirms the system is performing as expected.

Find certified radon mitigation contractors in your area to determine the best system for your home.

Codes and Standards Worth Knowing

The EPA’s radon program sets the national action level (4 pCi/L) that drives nearly every mitigation decision, and the American Association of Radon Scientists and Technologists publishes the consensus standards that mitigation systems are designed and tested against, including ANSI/AARST RMS-LB for residential mitigation and MAH for measurement that mitigation systems are designed and tested against. A mitigator who is AARST-certified and references the current ANSI/AARST standard for your installation type is working at trade-association level, not freelancing.

Frequently Asked Questions

How do I know which radon mitigation system I need? A certified radon mitigator runs a diagnostic pressure field test during the initial assessment. They drill a small test hole in the slab and measure how well negative pressure extends through the substrate. This determines how many suction points are needed and where to place them. Foundation type (basement, slab, crawl space) is the first indicator, but the diagnostic test confirms the right approach.

How loud is a radon fan? Most radon fans operate at 35–50 decibels — roughly comparable to a quiet conversation or a refrigerator hum. Fans installed in the attic or garage are barely noticeable inside the living space. Exterior fans are slightly more audible but still quiet. Fan noise shouldn’t be a concern for most homeowners.

Does a radon system work in all seasons? Yes. Radon systems operate year-round and don’t require seasonal adjustment. The fan runs continuously (24/7) to maintain consistent negative pressure under the foundation. Some homeowners notice slightly higher radon readings in winter when homes are sealed — if readings climb above 4 pCi/L with the system running, have the system inspected for a failing fan or compromised suction point. Our guides on why radon rises in winter and why levels stay high after mitigation cover both the normal seasonal bump and the warning signs of a real fault.

Can I add a second suction point later if needed? Yes. Adding suction points to an existing system is straightforward — it involves drilling an additional hole, connecting piping to the existing exhaust, and retesting. If a post-installation test shows levels aren’t low enough, adding a suction point or upgrading to a higher-powered fan are both common solutions.