Sub-Slab Depressurization Installation Explained

What is Sub-Slab Depressurization System Installation and how does it work?

Sub-slab depressurization (SSD) is the standard fix for radon in slab-on-grade and basement homes. It pulls radon from under the concrete slab and vents it safely above the roofline. Installation means creating a suction point, running a pipe, and adding a fan.

Think of your concrete slab as a lid over the soil. Radon gas seeps up from the ground and builds up under that lid. SSD flips the pressure: a fan draws a slight vacuum under the slab, so radon moves toward the suction pipe instead of drifting up through cracks and joints into your living space.

The pipe runs from the suction pit, up through an interior wall or along the outside of the house, and exits above the roof. That keeps the gas away from windows and doors. The fan, usually in the attic or on the exterior, runs continuously.

In Huntsville, where the Tennessee Valley sits on fractured limestone and shale, radon levels can run high. That's why SSD is the go-to method for slab homes here. It's proven, reliable, and works year-round.

Installation isn't a one-size-fits-all job. The crew has to find the best spot to pull suction, seal the pit properly, and route the pipe without compromising the roof. That's why a thorough on-site inspection matters more than a phone estimate.

• Suction pit dug through the slab, then sealed
• PVC pipe routed to a fan and vented above the roofline
• Manometer shows the system is working
• Fan runs continuously to keep pressure negative

How Sub-Slab Depressurization System Installation works, start to finish

Installation follows a clear sequence: inspect the slab and soil, cut the access hole, dig a suction pit, seal the pipe connection, run the pipe to the fan, and vent above the roof. Then the crew tests the system and shows you how to read the manometer.

We start by checking the slab for cracks, the sump pit, and any hollow spots. That tells us where the soil is most porous and where the suction will work best. In a Huntsville home with a crawl space or a partial basement, the approach shifts, but the principle stays the same.

Next, we cut a hole, usually 4 to 6 inches in diameter, through the concrete. Below that, we dig out a small pit, roughly a foot deep, to create an air pocket. That pocket lets the fan pull air from a wider area under the slab, not just from one tiny spot.

The pipe, typically 3-inch PVC, gets glued into a fitting that's sealed to the concrete with a high-grade urethane caulk. That seal is the difference between a system that works and one that just makes noise. If the seal leaks, you're pulling air from the house, not the soil.

From there, the pipe runs upward, often through a closet or garage, and out through the roof. On a two-story home, that can mean a longer run and a stronger fan. The fan mounts in the attic or on the exterior wall, and it's wired to a dedicated circuit.

Finally, we install a manometer, a small U-tube gauge that shows pressure. It's your at-a-glance check that the fan is pulling. We also run a post-installation radon test, usually a short-term test that takes 2 to 7 days, to confirm levels dropped.

The whole process, for a typical slab home, takes 4 to 6 hours. That includes the physical work, the sealing, and the cleanup. No need to move out, and you can use the house normally while the system runs.

1. Inspect the slab.We look for cracks, hollow spots, and the sump pit to pick the best suction location.
2. Cut and dig.A 4 to 6 inch hole is cut, and a foot-deep pit is dug to create the air pocket.
3. Seal the pipe.The PVC pipe is glued to a fitting and sealed to the concrete with urethane caulk.
4. Run the pipe.Route it up through a wall or exterior, and out above the roofline.
5. Install the fan.Mount the fan and wire it to a dedicated circuit, usually in the attic or outside.
6. Test and show.We set the manometer, run a post-test, and show you how to read it.

Why Sub-Slab Depressurization System Installation matters for your home

Radon is the second leading cause of lung cancer in the U.S., and Huntsville's geology makes it a concern. SSD is the most effective way to cut indoor radon levels, often by 90% or more. It's a permanent fix, not a band-aid.

The EPA sets the action level at 4 pCi/L, but even lower levels carry some risk. In North Alabama, where the soil is rich in uranium-bearing granite and shale, radon can easily exceed that. A neighbor's house might test at 2, while yours hits 8. It's that variable.

SSD doesn't just lower radon; it also helps with soil moisture and other soil gases. That musty smell in a basement often comes from the same pathway. By depressurizing the slab, you reduce the push of moist air into the house, which can help with humidity and odors.

The system runs silently in the background, using about as much electricity as a 60-watt bulb. It's a small price for the reduction in risk. And because the pipe is sealed and vented above the roof, the radon never re-enters through a window or vent.

For homebuyers, a radon mitigation system can be a selling point. If you're selling a Huntsville home that tested high, having a working SSD system already in place removes a major negotiation hurdle. Buyers see it as a feature, not a problem.

Putting off mitigation because levels are 'borderline' is a gamble. The EPA recommends fixing any home with 4 pCi/L or higher. Even at 2 or 3, the risk is not zero. A SSD system is the only way to know you're protected, short of constant testing.

• Radon is radioactive and decays into particles that can damage lung tissue
• Huntsville's fractured limestone and shale geology contributes to higher radon potential
• SSD reduces radon levels by 90% or more in most homes
• A manometer gives you a lifetime of simple monitoring

Common problems and what causes them

Most SSD problems come from poor sealing, undersized fans, or blocked suction points. A system that was installed wrong can fail silently, which is why regular manometer checks and a post-installation test matter.

The most common issue we see is a manometer that reads zero. That means the fan isn't pulling. It could be a tripped circuit, a fan that died, or a pipe that got disconnected. If you see zero, call us. It's not a DIY fix.

Another frequent problem: suction loss because the soil under the slab is too tight or too wet. Clay-heavy Huntsville soil can limit airflow. We sometimes need to add a second suction point or use a more powerful fan. That's why the initial inspection matters.

Poor sealing is a silent killer. If the pipe-to-slab seal leaks, the fan pulls air from the house, not the soil. You might hear the fan running, but the radon levels stay high. A proper urethane seal and a pressure test during installation prevent this.

Some homeowners try to save money by venting the pipe through a wall instead of above the roof. That's a code violation and a health risk, because radon can re-enter through windows. Our crew always terminates the pipe at least 12 inches above the roofline.

Finally, a system that was installed without a post-test is a guess. We always run a short-term test after installation to confirm the levels dropped. If they didn't, we fix it. That's the difference between a job done and a job done right.

Frequently Asked Questions